From waltah at earthlink.net  Fri Aug  6 23:09:02 2004
From: waltah at earthlink.net (waltah@earthlink.net)
Date: Fri Aug  6 23:20:40 2004
Subject: [HBR] Another Receiver Project -- HBR-4, Part 6
In-Reply-To: <41057AD1.2982.331B9DA@localhost>
References: <001a01c4735e$2028a070$2322fecf@DansDell>
Message-ID: <41140F8E.28385.248C6C7@localhost>

Well, I'm listening to it -- sort of.   With full volume I can hear 
signals, but the S-meter barely moves.

80 meters is working.   The 18 Mcs crystals I had oscillated over 
100 kcs high and were given to hopping to another mode/frequency 
nearby; it looked to me like they had been opened and 'adjusted.'   
I found a 6 Mcs rock that runs fine 3rd overtone at 18,046 kcs.   
Also two for 9.5 Mcs that should oscillate 3rd overtone at 28.600 or 
so -- close enough to test 20 meters.   (Crystals are 14 Mcs above 
high end of band.)

The ICM crystals -- correct frequencies for 80, 40, 30, 20, and 10A -
- should be here next week.   I really don't think I'll need them 
before then. 

The bandswitch and front end tuning coils are from an FT-101 so 
there's the potential for 11 bands, 160 through 10D, including 30 
and an 'aux' band that must be 10 Mcs or higher.   

Overall gain is very low, especially in the IF stages.   I tweeked the 
design in the direction of low gain, all the way through -- chiefly by 
using relatively large cathode resistors.  Now I will go back and 
adjust the other way.  

Coupling between the 6JH8 beam deflection mixer and the IF's 
probably isn't right either.   It's resonant and approximately 
balanced (output from plates is push-pull) but the match to the 
crystal filter is doubtful.   The filter response is 'bumpy' -- I don't 
know if that means load too high or load too low.

These tubes require both beam balance -- the beam needs to be 
centered between the plates by DC bias on the deflection plates -- 
and RF balance -- the two halves of the plate tank look 'equal.'   I 
do have the latter but the DC balance adjustment circuit isn't there. 
For initial testing I picked a tube that balanced better than the 
others and let it go at that.   That'll have to be fixed since there's an 
RTTY signal at 9001 kcs or so and accurate balancing will give 
considerable reduction of IF feedthrough.

The beam tube may need more drive.   That will wait until the IF 
gain and mixer-filter coupling are straightened out because more 
drive will mean more problems with spurious responses.

It sounds good but you can't tell much by that until the signal levels 
are correct.   

Walt 
KJ4KV
From waltah at earthlink.net  Sun Aug  8 17:03:48 2004
From: waltah at earthlink.net (waltah@earthlink.net)
Date: Sun Aug  8 18:12:21 2004
Subject: [HBR] Another Receiver Project -- HBR-4, Part 7
In-Reply-To: <41140F8E.28385.248C6C7@localhost>
References: <41057AD1.2982.331B9DA@localhost>
Message-ID: <41165CF4.17030.1FD51C7@localhost>

I raised the IF gain until the mixer noise (no RF stage) is plenty 
loud.  IF noise (with mixer pulled) is almost inaudible even at full 
volume -- all that seems right.

I believe all the pieces work as they can be expected to, but sure 
enough the system doesn't work.  Namely, the receiver's sensitivity 
is far too low, apparently because of inadequate drive to the 6JH8 
mixer.    There are two answers, either of which should work, but 
first, the details of the problem.

The VFO (5-5.5 Mcs) output is about 1 volt p-p.   The Butler crystal 
oscillator (crystals 14 Mcs. above upper end of each band) has an 
output modestly greater than that.   These signals are mixed by a 
pair of 6J6's each operating as a push-push mixer with opposite 
phase outputs coupled to the deflection plates of the 6JH8 mixer.   
The deflection voltage (premixer output) is about 1 volt p-p from 
plate to plate.   Squires (of Squires-Saunders SS-1R fame) said in 
a QST article on 7360's as receiver mixers that about 10 times that 
value is optimum.  

The SS-1R is the only commercial receiver I've found using a beam 
deflection mixer.   It's double conversion with each mixer driven 
directly from an oscillator -- a much easier way to develop the 
necessary voltage.   Like my design, there's no RF stage -- 
desireable for best strong-signal performance.

The beam-mixer ham receivers that I know of either use a 
preceding RF stage or are double conversion above 80 meters with 
another mixer and RF stage ahead of the beam tube.   The only 
premixed (single conversion) design is W1OMX's, which has a 
pentode RF stage.   There's a no-RF stage beam tube single 
conversion design in a hybrid receiver in the 5th edition RSGB 
handbook but it drives the mixer directly from a PLL'ed VFO.   

In other words, I'm not the first to get here.

The 2 x 6J6 mixer is doing about what it can do -- roughly zero 
conversion gain.   The crystal oscillator can't be flogged any harder 
as the HC-49 crystals have a tiny bit of drift -- ~10 cps -- when you 
switch bands, as it is.   I might get somewhat more from the VFO, 
but the price would be reduced stability: this is the best VFO I've 
built and I want to keep it that way.  And in any case, driving the 
pants off of a mixer of this type to get more output voltage will lead 
to distortion and more spurs.

One solution is to add an RF stage.   I left room to do that; it 
wouldn't be a big deal.   The stage wouldn't have to have much gain 
and could be optimized for large signal handling.   But every db of 
gain there pushes you closer to the limit of the 6JH8's signal 
handling capabilities -- that limit is independent of the deflection 
voltage, so running the tube with low deflection voltage doesn't  
help.

The other approach is to use a much higher gain premixer.   There 
are various ways to do that but the tidiest by far is to replace the 
two 6J6's with a single 6JH8.   These tubes were used in an 
occasional ham SSB transmitter and are able to develop enough 
output from oscillator-size signals to drive tubes delivering 10-20 
watts; they're not your dad's 6K8.  Input and output arrangements 
are the same as the pair of 6J6's, namely one single ended and 
one push-pull input with push-pull output.

That's the way I'll try; the only small problem is cutting out and 
replacing that chunk of chassis with a plate having a single 9-pin 
socket.   An hour's work, plus the (modest) wiring changes.

I did add the DC balancing voltage to the 6JH8 mixer deflection 
plates.   The RTTY signal at 9000 kcs is now gone.  A trap may 
still be needed but that's for later.

We'll see ...

Walt
KJ4KV


From waltah at earthlink.net  Thu Aug 12 11:39:28 2004
From: waltah at earthlink.net (waltah@earthlink.net)
Date: Thu Aug 12 11:52:16 2004
Subject: [HBR] Another Receiver Project -- HBR-4, Part 8
In-Reply-To: <41165CF4.17030.1FD51C7@localhost>
References: <41140F8E.28385.248C6C7@localhost>
Message-ID: <411B56F0.25342.813F7D@localhost>

The 6JH8 premixer has somewhat higher gain than the 2 x 6J6 
circuit did -- say 5 db more.   However it has *much* larger signal 
handling capability on the push-pull (deflection plate) input.  That 
input is from the Butler crystal oscillator.   

Unfortunately the strengths of a Butler oscillator are stability, 
waveform, and ease of design; it's not a high-output circuit.  Higher 
output circuits for overtone crystals are generally vfo circuits with a 
crystal inserted in series at a low impedance point; they can be 
tricky to get to operate reliably.

I'll stay with the Butler circuit for the time being. 

I got some increase by replacing the 12AT7 with a 12AU7; the 
greater grid voltage swing of the latter allows a higher plate voltage 
swing, hence higher output.   Another doubling of output voltage 
was obtained by increasing the number of turns on the secondary 
of the transformer coupling the oscillator to the premixer.   However 
I'm testing with the 18 Mcs (80M) crystal; there's the risk of self-
resonance at 10M where the frequency is 42.5 Mcs.   Or there may 
be too much stray capacity to allow tuning the plate coil on 10; 
making the coil smaller would hurt 80M output.

In any case the higher turns ratio represents a pretty good match 
to the premixer.  Unlike a grid the deflection plates actually draw 
some power -- about 0.1 mA at +8 volts.   You can bias the 
deflection plates negative a bit and reduce this considerably, while 
increasing the deflection sensitivity at the same time.  In this 
respect the 6JH8 is quite unlike the 7360 and 6ME8 which are 
supposed to be operated at +75 volts on the deflectors and will 
always draw significant deflector current.

There is a spare bandswitch section for the Butler oscillator so it 
would be possible to switch the coil on the high bands.   

Changing from direct drive from the premixer plate to mixer 
deflection plates to a step-up autotransformer circuit picked up 
another doubling of output.   Same possiblity of self-resonance or 
inability to tune the 10M band, also not checked yet.   

Increasing the VFO plate voltage from 38V to about 60 volts raised 
the premixer drive from 0.7V p-p to ~2V -- about the limit for 
reasonable linearity -- with no noticible increase in drift.  

The Butler crystal oscillator plate voltage was already maxed out.   
If I used the 70 volt negative bias on the cathode that might help, 
but the current drain would vary from band to band which would 
require regulating the bias line.   It may be necessary to switch 
oscillator circuits.

With those changes the gain of the mixer is adequate and S9 
occurs at 35-75 uV on 80 meters, the only band I'm testing right 
now.   However, the sensitivity is an unsatisfactory 3 uV for 6 db 
S+N/N -- should be 1 uV or less.  

The poor sensitivity does appear to be the mixer.  There are several 
possible reasons.  The tube is operating at about half the rated 
voltages, for one thing.  Also the drive probably still isn't quite up to 
optimum -- I cannot precisely measure it because of loading by the 
scope.   

The 6JH8 is in this application an extremely linear high gain 
pentode mixer.   Pentode mixers aren't known for being quiet.  The 
noise, however, doesn't come from the grid circuit, which I think 
means that a further increase of gain (=drive) should improve 
sensitivity.

On the positive side the thing is an excellent strong-signal 
performer.   On 80, I can hear anything anyone else can hear, and 
better than most.   No matter how lousy the conditions, if I can 
hear it I can copy it.   

The VFO is outstandingly stable ... drift is down for about 200 cps 
in the first few minutes, then small enough that I haven't measured 
it.  It's in the same ballpark with the crystal oscillator.  

There's still plenty to do.   In addition to the sensitivity issue the 
filter passband is excessively 'lumpy,' the calibrator isn't wired yet, 
only 80 meters is working (the crystals came yesterday), the front 
panel is unfinished, the S-meter zero drifts continuously, there's a 
strong spurious response that looks like a harmonic is involved 
near the low end of 80, the Butler oscillator tuning drifts 
excessively ... I'm sure there's more.  

Lessee ... 4x 5.4 Mcs = 21.6 Mcs; 21.6 -18 = 3.6 Mcs which 
would tune with the VFO at 5.4 Mcs.   That's it, I bet.   There's the 
price of high VFO drive -- it's probably pushing the 6JH8 premixer 
into a bit of grid current.   When you're dealing with signals of 
several volts you don't need a large percentage of distortion to get 
several microvolts of spur.   

The lumpy passband is probably due to mismatching the crystal 
filters.  I was extremely careful about feedback paths and the 
lumps don't change with IF tuning.   Some experimenting with the 
crystal filter loads will probably help.   First thing to do is to check 
my working Tempo One and see what that filter looks like there.   I 
know it's not great.   4 pole, for one thing.   

An interesting possibility for a future design is use of a beam tube 
premixer as a combination VFO-mixer, eliminating the separate 
oscillator tube.   A single-ended oscillator would be substantially 
isolated from both the deflection plate input and the output because 
both of those are push-pull; the circuit is shown in various sources. 

A disadvantage would be that these tubes don't have high gain 
when considered as amplifiers.  Transconductance as a pentode is 
about 4400 and using the screen as a plate for a Hartley or Colpitts 
circuit it would be considerably lower; the 6GK5 is about 15,000.   
This would definitely be a compromise VFO design, although the 
savings of a tube might make it worth trying for compact 
equipment.   

Walt
KJ4KV

From windy10605 at juno.com  Fri Aug 13 21:10:38 2004
From: windy10605 at juno.com (windy10605@juno.com)
Date: Fri Aug 13 21:16:21 2004
Subject: [HBR] Another HBR Project -- Chapter 9
Message-ID: <20040813.201038.1724.31.windy10605@juno.com>

Say Walt do you still have a documentation package available for your HBR
receiver ? I have all your notes on the CD I'm sure but I did not get a
copy of the diagram and chassis layout.

73 Kees K5BCQ
From waltah at earthlink.net  Sat Aug 14 16:11:39 2004
From: waltah at earthlink.net (waltah@earthlink.net)
Date: Sat Aug 14 16:24:55 2004
Subject: [HBR] Another Receiver Project -- HBR-4, Part 9
In-Reply-To: <411B56F0.25342.813F7D@localhost>
References: <41165CF4.17030.1FD51C7@localhost>
Message-ID: <411E39BB.20557.16F6679@localhost>

Two problems:

1.  When I installed the brand new 'proper' 80M crystal (18 Mcs), it 
drifted like crazy.   Whoops -- I had been using a 6 Mcs rock on 
the 3rd overtone.  The new crystal was a fundamental crystal 
because that's all ICM does at 18 Mcs.   But it is necessarily 
much thinner and the drive level that was perfectly okay for a 6 Mcs 
HC 49 working on the 3rd overtone was way too high for an 18 Mcs 
HC 49.

The answer to that might have been to find someone to make a 3rd 
overtone 18 Mcs crystal -- other companies do make them.   
However the 42.5 Mcs crystal for 10M (fundamental about 14 Mcs) 
wouldn't be much thicker than the 18 Mcs one.   This is a problem.

Basically the Butler oscillator power level has to be reduced. 

2.  Though I have adequate overall gain, the sensitivity was an 
unsatisfactory 3 uV for 6 db S+N/N.   That calls for greater mixer 
gain, in particular, I needed more drive to the mixer deflection 
plates.   That called for *more* output from the oscillators; since 
the VFO was already producing harmonics, the increased output 
would have to come from the Butler oscillator.

Whoops.

After some thinking, I decided that the answer was to reverse the 
oscillators.   The Butler osc. would do better into the control grid of 
the premixer where less signal is required; redoing the VFO as a 
push-pull oscillator would allow ample drive for the premixer 
deflection plates.   Heck, at 5 Mcs you can probably get five watts 
from a 6J6 with the sections in push-pull; there's not going to be a 
problem getting 10V p-p at a tiny fraction of an mA.

It was easier than it might sound.   I have to do the dial tracking 
from the start (had hoped to avoid that) but that shouldn't be more 
than a few hours of work.   The low warm-up drift of the 6GK5 
oscillator probably can't be acheived but if so, that's the price of 
using a more powerful, lower gain tube and a circuit that gives a 
less favorable oscillator parts layout.

The circuit is the push pull version of a grounded cathode Colpitts.   
Center tapped coil from plate to plate, caps from plates to opposite 
grids and from grids to ground.  (I invariably get the 'opposite' part 
wrong the first time, and this was no exception.)   The tuning cap is 
a two section with a section connected from each plate to ground.  
The coil tap floats; circuit symmetry is established by the plate to 
grid and grid to ground capacitors which are chosen to be most of 
the tank capacitance and should be pretty closely matched.  
Excellent waveform, plus output can be taken push-pull from the 
grids which are a relatively low impedance point.

The lower gain isn't quite the issue it seems because in a push-pull 
configuration there are two tubes.    But the push-pull circuits make 
it difficult to get isolation beween the tube and tank as you can with 
the Vackar or Clapp single ended circuits.  However, my 
impression is that the VFO is sufficiently stable.   

(The 6J6 was certainly the wonder of its day.  1942, perhaps?   It 
was among the very first miniature tubes, probably designed 
specifically for lower power radar applications like the APS-13 tail 
warning radar and APN-1 radar altimeter -- it was used as a pulsed 
self-oscillating transmitter in both sets, delivering I don't know how 
much peak power.   It oscillates pretty easily at 500 Mcs and 
delivers a few watts CW well into the VHF.   

(With a transconductance of 5300 mhos at 100 plate volts it's no 
slouch even by much later standards.   And it's quite beautiful to 
see in operation:  unlike the modern tubes with wimpy little 
filaments all wrapped up in electrodes, the 6J6 spills light all over 
the chassis.   A serious vintage 2M AM station would use a fistful 
of 'em on an open chassis, ending up with maybe a pair of 15Es?  
8025s?  We're talking *decorative* here, not *practical* so an  
832A is out.

(Another project for another day.

(The 6J6 is a highly satisfactory push-pull audio output stage, too, 
delivering the few hundred milliwatts needed for the usual 'station 
filling' volume without a problem.   And I have used 6J6's as push-
push mixers at HF with very good success.)

With the oscillators rearranged I've got way more overall gain than 
is desirable -- the meter pins on any reasonably strong signal.   So 
the IF gain needs to be cut back some ... that's easy enough to do! 
Probably the first step is to adjust the crystal filter loads for a flatter 
passband, since that may lead to a reduction of gain.   As a plus, 
all the connections in the oscillator/premixer area got much shorter 
because the pin layout of the 6JH8 favors this oscillator 
arrangement.  

I finally wired up the calibrator.   *That*, at least, worked the first 
time.    There's space for and I really will add a 25 kcs multivibrator. 
Yeah, another 6J6.   

Sure enough, the 'birdies' are stronger than they were and I'm sure 
there will be more problems but I'm feeling pretty good about the 
project right now.   

Walt
KJ4KV
From N2EY at aol.com  Sat Aug 14 20:55:27 2004
From: N2EY at aol.com (N2EY@aol.com)
Date: Sat Aug 14 20:59:30 2004
Subject: [HBR] Another Receiver Project -- HBR-4, Part 9
Message-ID: <1d2.28a53aa2.2e500e7f@aol.com>

In a message dated 8/14/04 4:21:36 PM Eastern Daylight Time, 
waltah@earthlink.net writes:


> the Butler oscillator 
> 
> 

refresh my memory...

why a Butler oscillator, rather than a conventional triode overtone?

73 de Jim, N2EY
From hbrnut at earthlink.net  Sat Aug 14 22:21:39 2004
From: hbrnut at earthlink.net (Darrell, WA5VGO)
Date: Sat Aug 14 22:25:36 2004
Subject: [HBR] IFT for BFO Coil
Message-ID: <5.2.0.9.2.20040814211551.00b1c410@mail.earthlink.net>

Has anyone had any experience converting an I.F. transformer to a BFO coil? 
I have a 100 kC transformer. It has a 110 pF capacitor across the coil. I 
assume if I replace this with a 470 pF and 150 pF in series, that this will 
keep the coil resonate and provide me with my feedback connection. Is it 
this simple?

Regards,
Darrell, WA5VGO


From ak0b at swbell.net  Sun Aug 15 07:29:13 2004
From: ak0b at swbell.net (Stan Wilson)
Date: Sun Aug 15 07:33:20 2004
Subject: [HBR] IFT for BFO Coil
In-Reply-To: <5.2.0.9.2.20040814211551.00b1c410@mail.earthlink.net>
Message-ID: <000701c482bb$17eb0530$0101320a@CPU>

Darrel I think the result of 470 and 150 is 320 pf ?  I always use the
rule of thumb to subtract in series and add in parallel will be very
close to resultant value.  
Stan


-----Original Message-----
From: hbr-bounces@mailman.qth.net [mailto:hbr-bounces@mailman.qth.net]
On Behalf Of Darrell, WA5VGO
Sent: Saturday, August 14, 2004 9:22 PM
To: hbr@mailman.qth.net
Subject: [HBR] IFT for BFO Coil

Has anyone had any experience converting an I.F. transformer to a BFO
coil? 
I have a 100 kC transformer. It has a 110 pF capacitor across the coil.
I 
assume if I replace this with a 470 pF and 150 pF in series, that this
will 
keep the coil resonate and provide me with my feedback connection. Is it

this simple?

Regards,
Darrell, WA5VGO


************************************
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From Bill at LizCurtisHiggs.com  Sun Aug 15 08:00:08 2004
From: Bill at LizCurtisHiggs.com (Bill Higgs)
Date: Sun Aug 15 08:04:09 2004
Subject: [HBR] Re: Another receiver project
Message-ID: <020601c482bf$68e06f80$6500a8c0@BILLDESKTOP>

Waltah and the group,

I was noting with interest the HBR-4, and also noting with interest the late W1KLK's design in Feb '72 QST (an experimental receiver for 75-meter DX work, p. 41). Doug used a low-gain RF stage with a grounded grid dual triode . . . the RF stage used dual tunable Cohn filters, so the point was only to make up the loss in the filters, about 5-6 dB. He used a 7044 "computer" tube; your beloved 6J6 might well work here also. Interesting; should be stable in grounded grid mode. Mixer is the venerable 7360, driven unbalanced by a series-tuned 6U8A VFO/buffer.

The design of the BFO is of interest, as it looks as though it might be modified a bit for push-pull output by using the buffer (tetrode) stage of the 6U8A as a phase splitter, replacing the RFC with a resistor and taking outputs from the plate and cathode. Probably would reduce the output by half, but you'd get it back in absolute voltage difference at the deflection plates. Dunno if you've biased the deflection plates in your mixer or not (the 7360 requires 25V or so bias, the 6JH8 allegedly does not) . . . I don't know if biasing the plates positive affects the overall conversion gain of these tubes. My NEXT project after the HBR-??(WAY ahead of myself here) will be a project using the 6JH8 as a mixer and a pair of 6EH7 frame grid tubes in the IF; probably for 20 meters with another 6EH7 as an RF stage.

Doug's IF is 455Kc with a Collins filter, followed by a Q Multiplier stage set up for notch mode. The rest of the set is fairly conventional.

Work on the HBR-?? is going to be suspended for several weeks, pending the relocation of my shop. The termites finally won.

Bill Higgs, NT4C
From waltah at earthlink.net  Sun Aug 15 11:52:10 2004
From: waltah at earthlink.net (waltah@earthlink.net)
Date: Sun Aug 15 12:05:37 2004
Subject: [HBR] IFT for BFO Coil
In-Reply-To: <5.2.0.9.2.20040814211551.00b1c410@mail.earthlink.net>
Message-ID: <411F4E6A.25803.5B9310@localhost>

Darrell, WA5VGO wrote:

> Has anyone had any experience converting an I.F. transformer to a
> BFO coil? I have a 100 kC transformer. It has a 110 pF capacitor
> across the coil. I assume if I replace this with a 470 pF and 150
> pF in series, that this will keep the coil resonate and provide me
> with my feedback connection. Is it this simple? 

470 * 150 / (470 + 150) = 70,500 / 620 = 113.71   That's close 
enough!

Cap A *times* cap B divided by (cap A *plus* cap B) -- same 
formula as resistors in parallel.

That'll give you the tank circuit for a Colpitts oscillator.   In the 
traditional Colpitts the cathode of the tube would be connected to 
the junction of the two caps; you'd need a way to ground that for 
DC so the plate current has a place to go.  At higher frequencies a 
choke would work but the choke for 100 kcs is awkwardly large.    I 
suggest instead using a grounded-cathode variant of the Colpitts 
circuit: 

Ground the cathode of the tube directly, also the junction of the two 
capacitors as above.  

Feed the grid through a cap from the 150 mmf end of the coil -- I 
suppose 470 mmf or so, and this cap must handle the high voltage 
from which the stage will be run.   Grid leak as usual.   

Hook the other end of the coil to the plate of the tube directly.   
(Coil is at full plate voltage.)   Feed the plate through a resistor of 
100k, more or less according to power output requirements.   Any 
of the usual medium-mu triodes will work.

Output may be taken from the plate through a few mmf.

If the BFO must be adjustable over a few kcs from the front panel 
connect a suitable variable cap from either end of the coil to ground.
Tuning range fraction will be roughly *half* the ratio to which ever of 
the two tank caps it shunts times the ratio of 1/reactance of the 
shunted cap to the total.   This tuning cap must also handle full 
high voltage.

For example a 15 mmf variable across the 150 mmf fixed cap 
would give:

1/2 * 15/150 * 114/150 = 3.8% tuning range or about 3.8 kcs.   

This is also an excellent VFO circuit because the cathode of a 
tube is the squirreliest electrode of them all -- think of a poor 
quality capacitor between the cathode and the filament shunted by 
a poor quality diode with a low breakdown voltage rating, both with 
very high temperature coefficients -- and the filament usually runs 
on AC.   All the usual hot-cathode VFO circuits *will* have 60 cps 
FM at VHF.

Using modern tubes you can isolate the tube from the tank circuit 
well enough that for HF service you can live with the crummy 
cathode.  With lower gain tubes it's well to consider putting the 
filament at cathode voltage for RF -- the command transmitters ran 
the oscillator filament through parallel windings on the VFO coil, 
did they not?   

When using the grounded cathode Colpitts in a high-stability VFO, 
consider tapping the coil to feed the plate voltage.   (Floating tap -- 
not bypassed.)  That way you don't have the plate feed resistor 
across part of the tank circuit, lowering the Q.   In a 100 kcs BFO 
this is not an issue because the Q is already low enough that 
realistic plate feed resistors will make no difference.

In theory a choke is the answer but in high-stability VFO practice 
chokes are to be avoided because they have the worst temperature 
coefficient of all parts.

Walt 
KJ4KV

From waltah at earthlink.net  Sun Aug 15 12:11:54 2004
From: waltah at earthlink.net (waltah@earthlink.net)
Date: Sun Aug 15 12:25:21 2004
Subject: [HBR] Another Receiver Project -- HBR-4, Part 9
In-Reply-To: <1d2.28a53aa2.2e500e7f@aol.com>
Message-ID: <411F530A.17079.6DA464@localhost>

Jim, N2EY wrote:

> refresh my memory...
> 
> why a Butler oscillator, rather than a conventional triode overtone?

Laziness or perhaps sheer poor judgement?   A Butler circuit 
(which is just a cathode coupled multivibrator with a series mode 
crystal between the cathodes) will *always* work right off.   The 
others seem generally to take some tinkering to get working.   

This is particularly true when the oscillator must work with the 
same coil and preset capacitor adjustements with various crystals 
over a wide range -- here, 16 Mcs (for 160M) to 43.5 Mcs (10D).   
But I did make a single triode work in the HBR2K with an even 
slightly wider range, so it can be done.

The Butler gives better stability for variations in tube and tank 
parameters because there's greater total gain available but that's 
rarely an issue in ham practice.   

The Butler is also a very simple circuit.   

But for equal crystal current it has less output voltage because the 
plate voltage swing is limited by the grid to ground voltage swing.   
In other circuits there's some sort of voltage divider there and the 
plate swing is greater.

I expect that with the rearranged circuit -- push-pull VFO and single-
end output from the Butler crystal oscillator -- I'll be able to reduce 
the input and get satisfactory stability even from the new 18 Mcs 
crystal.    We'll see ...

Walt
KJ4KV

From waltah at earthlink.net  Sun Aug 15 12:46:34 2004
From: waltah at earthlink.net (waltah@earthlink.net)
Date: Sun Aug 15 13:00:02 2004
Subject: [HBR] One Month HBR Doc Package (was 'Another HBR Project --
	Chapter 9')
In-Reply-To: <20040813.201038.1724.31.windy10605@juno.com>
Message-ID: <411F5B2A.17717.8D6255@localhost>

Kees asked:
> Say Walt do you still have a documentation package available for
> your HBR receiver ? I have all your notes on the CD I'm sure but I
> did not get a copy of the diagram and chassis layout. 

I never did that documentation package.   There seemed to be no 
interest in it and documentation is a whole lot of work.   

Plus -- if you can believe this -- it's still under development.   About 
three months back I added an IF stage at 1665 kcs (1st IF) and 
now need to go back and add cathode resistors for that stage to 
each of the coil sets (I'm sure there's a spare pin available 
somewhere!) so that the overall gain will be the same on all the 
bands.   

Possibly then ... it did turn out quite nicely as a 'vintage design' 
vintage piece.   And while the mechanical issues of plugging in the 
coils through the panel are substantial, electronically it's an easy 
set to get working because the gain is distributed over all possible 
frequencies -- an RF stage, a single stage each at 1665 and 85 
kcs, and finish up at audio.   

Stability's quite good, considering, because of the cooling of the 
coils by inward/upward air flow.  

The coils are no fun though -- the space in the command set coil 
cans is so limited that I haven't been able to find room for 
compensating caps in there!   

Also I *think* I know why those command set 85 kcs IFTs have 
such poor skirt selectivity.   The wires that connect the plug on the 
bottom to everything inside run up very close to the (large!) coils 
and the outside of the coils is 'hot.'   Thus there's substantial 
coupling past the tuned circuits.  It didn't matter in 'range receiver' 
use -- might even have been an advantage to be able to hear a 
strong station that was somewhat mistuned -- but it's a serious 
flaw in communications work.

It is possible to put a bit of grounded tin between the wire and coil 
in these places to provide shielding and I have been doing that, one 
transformer at a time, as I feel inclined to remove four or more wires 
and eight tiny screws.  

More to come on that topic.  

Walt
KJ4KV 



From N2EY at aol.com  Sun Aug 15 14:55:32 2004
From: N2EY at aol.com (N2EY@aol.com)
Date: Sun Aug 15 14:59:52 2004
Subject: [HBR] Another Receiver Project -- HBR-4, Part 9
Message-ID: <12f.48d6837e.2e510ba4@aol.com>

In a message dated 8/15/04 12:22:01 PM Eastern Daylight Time, 
waltah@earthlink.net writes:


> A Butler circuit 
> (which is just a cathode coupled multivibrator with a series mode 
> crystal between the cathodes) will *always* work right off.   The 
> others seem generally to take some tinkering to get working.   
> 

Well, I've always had good (overtone) luck with the classic circuit in the CW 
Crystals flyer, whether I used a 6U8 triode or half a 12AX7 (as in the 
HW-101). Same circuit will work with fundamentals as well.

Nowadays (Type 7) I use all fundamentals, using a 6AU6A or 6CB6 in the 
grid-plate circuit, Shamelessly copied from the "Sideband Package" article. This 
circuit can multiply in the plate circuit, too. Oodles of output and easy on the 
rock if the screen voltage is low (I use 75-150 volts).

73 de Jim, N2EY
From waltah at earthlink.net  Sun Aug 15 15:36:04 2004
From: waltah at earthlink.net (waltah@earthlink.net)
Date: Sun Aug 15 15:49:48 2004
Subject: [HBR] Re: Another receiver project
In-Reply-To: <020601c482bf$68e06f80$6500a8c0@BILLDESKTOP>
Message-ID: <411F82E4.11147.1289757@localhost>

Bill Higgs wrote:
> I was noting with interest the HBR-4, and also noting with interest the
> late W1KLK's design in Feb '72 QST (an experimental receiver for 75-meter
> DX work, p. 41). Doug used a low-gain RF stage with a grounded grid dual
> triode . . . the RF stage used dual tunable Cohn filters, so the point was
> only to make up the loss in the filters, about 5-6 dB. He used a 7044
> "computer" tube; your beloved 6J6 might well work here also. Interesting;
> should be stable in grounded grid mode. Mixer is the venerable 7360,
> driven unbalanced by a series-tuned 6U8A VFO/buffer.

Single band receivers are a whole 'nuther ballgame.   The '75-meter 
DX work' receiver looks excessively complicated for the job.   I 
really think that sensitivity better than about 1 uV is wasted on 
75/80 meters -- and that was *before* computers brought us whole 
new spectrums of RF 'dirt.'   

For a single band receiver you don't have much of a problem with 
high drive levels -- just run a push-pull oscillator using a 6J6 or 
perhaps that 7044; there should be enough gain even with no RF 
stage and even with a bit of loss in the input circuits.   I probably 
need to read the article to know why he used a bandpass input 
circuit.   Yes, it eliminates tuning but by his judgement it forced 
another stage.

Geez ... it's not a problem to *gang* the tuning for a single band 
receiver and doing so makes the absolute best use of a wide-
dynamic range mixer.
> 
> The design of the BFO is of interest, as it looks as though it might be
> modified a bit for push-pull output by using the buffer (tetrode) stage of
> the 6U8A as a phase splitter, replacing the RFC with a resistor and taking
> outputs from the plate and cathode. Probably would reduce the output by
> half, but you'd get it back in absolute voltage difference at the
> deflection plates. 

What you get into is that tube capacitances effectively bypass the 
phase splitter outputs.   This isn't a problem at low enough 
frequencies but at a few Mcs it gets you, unless you use such low 
load resistances that output goes to nil.   (The plate load is in 
series with the tube's plate resistance.)  The frequencies for which 
push-pull output might be needed (and not easily available just by 
using a push-pull oscillator circuit) are 16-44 Mcs in this project ... 
that's out of the range for phase splitters.

> Dunno if you've biased the deflection plates in your mixer or not
> (the 7360 requires 25V or so bias, the 6JH8 allegedly does not) . .
> . I don't know if biasing the plates positive affects the overall
> conversion gain of these tubes. 

The data sheets for the 6JH8 claim that maximum deflection 
sensitivity occurs at -14 volts on the deflection plates but that's at 
250 plate volts.   I'm running mine at 130 plate volts and -7 volts on 
the deflectors.   I don't know if that's optimum or not, but it works 
okay.   

Conversion gain is proportional to the amount of deflection, so the 
slight negative bias is good for gain, as well.   And an added plus -- 
with some negative bias, the tube draws negligible deflector current 
so the deflection *power* and loading of the driving tuned circuit 
should go down considerably.

> My NEXT project after the HBR-??(WAY ahead of myself here) will be
> a project using the 6JH8 as a mixer and a pair of 6EH7 frame grid
> tubes in the IF; probably for 20 meters with another 6EH7 as an RF
> stage. 

That sounds like a good plan.   I don't know what would be the best 
possible 6JH8 noise figure on 20M but considering the greater 
difficulty of getting good tuned circuits on this band and above, an 
RF stage sounds wise.   

I don't understand all I know about noise and the beam deflection 
mixer, but the input noise of the 6JH8 in this project is *inaudible*.  
That is, with the antenna disconnected there is nothing you can 
peak by tuning the grid through resonance.   The tube definitely 
generates some noise (in fact nearly all of it, in this application) but 
it's just the electron stream.    And the noise doesn't vary with the 
drive level -- I can pull the premixer and the noise remains the 
same.   So increasing the drive level just raises the output without 
a corresponding increase of noise.   

I'm using the 6JH8 with no RF stage and *3* 6EH7 IF's in the HBR-
4 and that seems the right amount of gain, with the higher drive 
levels I'm now using.
 
> Doug's IF is 455Kc with a Collins filter, followed by a Q Multiplier stage
> set up for notch mode. 

455 kcs IF's and mechanical filters both seem like anachronisms 
now.   (*So* 1950's ...)  You can't possibly get adequate image 
rejection at that frequency so you're forced to a multiple conversion 
design.   And crystal filters for the low HF are both easy to design 
and dirt cheap, using microprocessor clock crystals.   

One can either go with an existing conversion scheme, trusting the 
designer thereof to keep you out of trouble, or take paper and 
pencil and strike out on your own.   Right now, I'm wishing I hadn't 
had 9 Mcs filters on hand, because I'm certain I could have gotten 
that 3.6 Mcs spur out of the band with just a slight jiggering of the 
IF and VFO frequencies.    Probably I can get the amplitude down 
considerably with some adjustment of operating conditions, but it's 
hundreds of uV -- it's not going completely away.

Humm ... maybe that's what I'll do eventually -- make my own 
filters in the same size packages but for a slightly different 
frequency.   

Actually, you can do this kind of adjustment by varying any two of 
the IF, the VFO range, and the band crystal frequencies.  

> Work on the HBR-?? is going to be suspended for several weeks, pending the
> relocation of my shop. The termites finally won.

They do that ...

Walt
KJ4KV


From hbrnut at earthlink.net  Sun Aug 15 17:47:45 2004
From: hbrnut at earthlink.net (Darrell, WA5VGO)
Date: Sun Aug 15 17:52:19 2004
Subject: [HBR] IFT for BFO Coil
In-Reply-To: <411F4E6A.25803.5B9310@localhost>
References: <5.2.0.9.2.20040814211551.00b1c410@mail.earthlink.net>
Message-ID: <5.2.0.9.2.20040815163848.00b309c0@mail.earthlink.net>

Walt,

Thanks very much for the BFO advice. It sounds almost fool proof. I had not 
considered the problem with the RF choke, but fully understand your point. 
It would take many mH to be effective at that low of a frequency. I assume 
my ratio between the capacitors is okay? I plan on using a 6C4. All of my 
experience with oscillators has been the tapped coil variety.

73,
Darrell, WA5VGO





From waltah at earthlink.net  Sun Aug 15 20:36:58 2004
From: waltah at earthlink.net (waltah@earthlink.net)
Date: Sun Aug 15 20:50:21 2004
Subject: [HBR] IFT for BFO Coil
In-Reply-To: <5.2.0.9.2.20040815163848.00b309c0@mail.earthlink.net>
References: <411F4E6A.25803.5B9310@localhost>
Message-ID: <411FC96A.20551.23C1E2A@localhost>

Darrell, WA5VGO wrote:

> Thanks very much for the BFO advice. It sounds almost fool proof. 

You've been reading my adventures with HBRs, so you know how 
'fool proof' my ideas are ... Hi!

They may be proof against most fools but *I* get into trouble quite 
regularly.   Yep, I'm the guy who feels he has made progress with 
this receiver project because on *this* one, I only hooked up two 
tube filaments wrong.

> I had not considered the problem with the RF choke, but fully
> understand your point. It would take many mH to be effective at
> that low of a frequency. 

Since the original tank capacitor was 100 mmf, the coil must be 
around 20 mH for resonance at 100 kcs.  Thus unless you used a 
choke of at least a few hundred mH -- that is, maybe half a henry 
or so! -- a lot of the tank current would actually flow in the blocking 
choke.   You might get the oscillator working like that, but I 
guarantee problems.

> I assume my ratio between the capacitors is okay? 

It sounds right to me.  1:3 is a very common ratio for cathode 
section to grid section in these oscillators.

> I plan on using a 6C4. All of my experience with oscillators has
> been the tapped coil variety. 

A 6C4 should work fine and will be less trouble than a 'hotter' tube.  
Tapped coil or capacitive voltage divider makes no difference to the 
RF; it's strictly a DC issue and you can deal with that.

Walt 
KJ4KV
From waltah at earthlink.net  Tue Aug 17 17:37:36 2004
From: waltah at earthlink.net (waltah@earthlink.net)
Date: Tue Aug 17 17:51:32 2004
Subject: [HBR] A Question About Handbooks
Message-ID: <41224260.9704.1E16D24@localhost>

The other night I got to looking at the Radio Amateur's Handbook.   
In my collection, '69 is the last 'good' book, the next one that I have 
is '72 and it marks the start (in my collection) of the beginning of 
the current 'Revenge of the Nerds' books, tuned for engineers -- 
presumeably those without a normal collection of engineering 
handbooks -- rather than hams.   

First question -- what about the '70 and '71 books?   Are they RON 
books or do they continue the earlier tradition?

I notice that the '69 book lists Doug DeMaw, W1CER, as editor; '72 
lists him with several others as an associate editor, one Douglas 
Blakeslee, W1KLK, as editor.  

Second question -- there has to be a story there.  Does anyone 
know what it is?   

Walt
KJ4KV
From waltah at earthlink.net  Tue Aug 17 17:24:19 2004
From: waltah at earthlink.net (waltah@earthlink.net)
Date: Tue Aug 17 17:51:35 2004
Subject: [HBR] Another Receiver Project -- HBR-4, Part 10
In-Reply-To: <12f.48d6837e.2e510ba4@aol.com>
Message-ID: <41223F43.15344.1D54369@localhost>

The AGC problems seem to be straightened out.   The big problem 
was slight gas in two of my three 6EH7 IF tubes.   I need to pull 
out the tube tester and go through all of the spares.  

The one month HBR  had the same problem so I was a little 
quicker to try substituting tubes this time.   The symptom is that 
the AGC buss doesn't want to sit near zero ... either it goes to 
positive voltage (from the grid of the gassy tube) or enough negative 
voltage that that tube doesn't flow positive current.   But of course it 
takes a while to focus on the symptoms.

40 meters is working.   Adding the other bands is harder than I 
expected because there are wrong crystal modes and wrong 
mixing products that aren't that far off.   Basically you have to set it 
all up with a GDO before turning on the power.   Guess how I 
learned that?

Getting rid of the gassy tubes seems to have mostly fixed the filter 
passband.   Guess one of the bad tubes was loading the filter.  

I'm actually using two filters -- one in the usual place, right behind 
the mixer, and the other at the end of the IF, right before the 
detectors.   Haven't checked the skirts yet or the ultimate rejection 
but they should be good enough!

The passband was four bumps, symmetrical, with the center two 
maybe 6 db higher than the sides.   Now it's nearly flat -- just four 
tiny bumps.

It's the easiest receiver to tune on an SSB signal of any I've used.   
I think that's because the product detector is so good that you 
don't have extra voice harmonics to get right. 

The crystal oscillator is still a problem.   Jim can you describe the 
standard circuit you mentioned?   I'm going to try changing that; 
there are too many 'issues' with what I'm doing.

When I have a CO that works well, I'll set about optimizing the 
output level -- sensitivity vs. spurious signals.

The new push-pull VFO has been no problem at all.  It drifted 
steadily downward for a few hundred CPS and the second try at 
compensation -- a 3 mmf command set N750 ceramic cap on the 
6J6 socket -- pretty nearly eliminated that.   I'll probably rewire that 
socket -- there are so many parts there that access to make 
changes is quite difficult and I really should shorten the cap leads 
to get more and faster compensation.

There are always surprises -- usually the crystal oscillators are 
trivial and the VFO is a problem.

Walt
KJ4KV





From Bill at LizCurtisHiggs.com  Tue Aug 17 22:09:37 2004
From: Bill at LizCurtisHiggs.com (Bill Higgs)
Date: Tue Aug 17 22:14:11 2004
Subject: [HBR] Re: W1KLK receiver
Message-ID: <00a701c484c8$69deef00$6500a8c0@BILLDESKTOP>

Walt and the gang,

I'll begin by correcting myself on describing the input circuit: Not a Cohn, but two double-tuned circuits with bottom coupling. Doug claimed about a 25KC bandwidth, sounds about right with the number of poles used with decent inductors. Some loss, hence the 7044 grounded grid stage even on 75 meters.

Walt, you're right on several counts: Noise levels on 75 are so high that additional sensitivity simply means more noise off the antenna. If a signal has to be 3 microvolt to be copied above the noise, sensitivity is not what you're needing. Doug's purpose with the elaborate RF stage is to eliminate the image; with a 455KC IF, you generally need all the front end image rejection you can get.

As far as the 455KC IF is concerned, Doug used what he had. The image rejection he was seeking IS possible on 75 with a 455KC IF, but you have to jump through a lot of filter hoops to do it - which is what he did. Anachronistic? Possibly; HF crystal filters had been around a few years when he designed the receiver. Still, the better Collins filters had excellent skirt selectivity and good ultimate rejection. The major drawback is insertion loss; some of the better filters also had 10-12 dB insertion losses. Hence, often an extra IF stage was needed (Doug's design had three, plus the Q-Multiplier).

I apologize for missing the first part of the project, and didn't realize you were using such a high injection freq. You're right, at that frequency the tube capacitances tend to shunt the outputs to each other; unless that particular reactance is tuned out (impractical with a VFO), output can drop significantly. 'Twas just a random thought . . . I might experiment with it a lower frequency.

Regarding the 6JH8 mixer: Thanks for the biasing info. While I have seen circuits using the tube as a balanced modulator without bias, it seems to me that at least some DC bias (either way) would allow for a pot to balance the tube. -7 volt shouldn't be too hard . . . are you using a negative supply or developing the voltage via a cathode resistor?

Again, thanks for the hints!

Bill Higgs, NT4C
From N2EY at aol.com  Wed Aug 18 07:16:56 2004
From: N2EY at aol.com (N2EY@aol.com)
Date: Wed Aug 18 07:21:50 2004
Subject: [HBR] Re: W1KLK receiver
Message-ID: <8e.128ea4a4.2e5494a8@aol.com>

In a message dated 8/17/04 10:39:24 PM Eastern Daylight Time, 
Bill@LizCurtisHiggs.com writes:


> Doug's purpose with the elaborate RF stage is to eliminate the image; with 
> a 455KC IF, you generally need all the front end image rejection you can get.

Agreed but I read the article a bit differently.

I think you could get adequate image rejection without all those tuned 
circuits. What 'KLK wanted was not just image rejection but rejection of strong 
out-of-band signals - meaning anything more than a few dozen kHz away from the 
desired signals. If the signals don't reach the mixer, it doesn't have to deal 
with them. 

If I understand the process, we hams measure 3rd order IM by injecting two 
relatively close-spaced signals into the rx and raising the level until an 
inband distortion product shows up. Typically it's two signals 20 kHz on 20 meters. 


Such a test gives a good indication of the dynamic range of the front end 
with a few very strong, closely spaced signals. But "in real life", many 'modern' 
receivers inhale huge chunks of spectrum and run it through several stages 
before there's any significant selectivity. If there are two or more properly 
spaced big sigs, you've got chatter. What 'KLK did was to cut down the number of 
big signals that even reached the mixer. Not just images but any strong 
out-of-band signals. 

I don't know if the HF spectrum is more or less crowded than it was back 
then. From what I recall, HF used to be stuffed full of high power RTTY, CW and 
'phone stations for a variety of services. SWBC, military, maritime, etc. 

Note the story about how he loaned the rx to the Novice across the way. The 
Novice's 75 watter desensed his regular rx (probably a 75A-4 or 75S3) but the 
Novice had no idea 'KLK was even on the air. In those days the Novice band was 
3700-3750, just below where the DX 'phones hung out, but far enough away that 
the front end selectivity would knock down 'KLKs big signal before it got to 
the mixer. Not so with the 'regular' receiver!.

> 
> As far as the 455KC IF is concerned, Doug used what he had. The image 
> rejection he was seeking IS possible on 75 with a 455KC IF, but you have to jump 
> through a lot of filter hoops to do it - which is what he did. Anachronistic? 
> Possibly; HF crystal filters had been around a few years when he designed the 
> receiver. Still, the better Collins filters had excellent skirt selectivity 
> and good ultimate rejection. The major drawback is insertion loss; some of the 
> better filters also had 10-12 dB insertion losses. Hence, often an extra IF 
> stage was needed (Doug's design had three, plus the Q-Multiplier).
> 

The Q multiplier was primarily for a rejection notch.

The three IFs were there for a couple of reasons. First, the lowgain RF amp 
meant the mixer output was pretty low, so three stages more than made up for 
it. Second, it can be easier to stabilize an IF strip if you don't try to get 
every last dB of gain out of each stage. 

But I think the most important reason (to him) was AGC range. With three 
supercontrol IF tubes on the AGC line, it doesn't take a lot of AGC swing to have 
a flat characteristic. IIRC, he did not apply AGC to the front end, so he 
needed to make up for that. I recall something like 40 dB gain control range per 
stage?

The W1KLK receiver has influenced many of my receiver designs. Not just 
electrically but mechanically. 

73 de Jim, N2EY
From waltah at earthlink.net  Wed Aug 18 10:26:21 2004
From: waltah at earthlink.net (waltah@earthlink.net)
Date: Wed Aug 18 10:40:19 2004
Subject: [HBR] Re: W1KLK receiver
In-Reply-To: <8e.128ea4a4.2e5494a8@aol.com>
Message-ID: <41232ECD.29129.5CE4DA@localhost>

This is an interesting discussion.

Bill said:
> > Doug's purpose with the elaborate RF stage is to eliminate the image; with 
> > a 455KC IF, you generally need all the front end image rejection you can get.

A 455 kcs IF works fine for an 80-only receiver.   At 3900, the LO 
will be at 4355 and the image at 4810; that's a pretty substantial 
distance away and even one decent-Q RF tuned circuit will take it 
out unless there's a very strong signal there.   However 455 kcs 
was always a problem with multiband receivers on 20M and above, 
frequently also on 40 because of the strong signals from the 
SWBC band in that area.

In the 60's, the region around 5 Mcs was still in use by the military 
for various mostly low-power applications.  It wasn't a bad place to 
have an image response.

On 10M, the less expensive ham receiver designs had two bands 
of equal sensitivity located 910 kcs apart.  
 
Jim said:
> Agreed but I read the article a bit differently.
> 
> I think you could get adequate image rejection without all those
> tuned circuits. What 'KLK wanted was not just image rejection but
> rejection of strong out-of-band signals - meaning anything more
> than a few dozen kHz away from the desired signals. If the signals
> don't reach the mixer, it doesn't have to deal with them. 

Yep.   For 80M, however, he probably could have used the 7360 
mixer 'barefoot' and done even better; there's no serious problem 
coupling two or three tuned circuits without a tube between if you 
are only covering 500 kcs at 80M.  

I don't know what the ultimate sensitivity of the beam tubes is as 
mixers but it's pretty good.   I've got 0.25 uV on 40 meters with no 
RF stage and two tuned circuits preceding the mixer.  For a single 
band receiver you could use a push-pull 6J6 oscillator, with 12AT7 
cascode buffer if needed (probably not) -- the design should be a 
cinch.   With just one oscillator he wouldn't have the problems I 
have with spurious responses.  

The purest would probably use both 'top' coupling for the front end 
coils (with a small cap between the tuned circuits) and 'bottom' 
(with a shared small coil at the bottom so the gain could be leveled 
across the band.   In a bandswitched receiver you run out of space 
pretty fast with so many parts but for a single band it's surely not a 
problem.

An interesting design would be plug in front ends, with different 
VFOs according to the band.  You could even use different 1st IFs 
and convert to a common IF to do most of the amplification in the 
mainframe.   Four tubes, maybe, in the plug-in unit and the rest on 
the mainframe.   

> If I understand the process, we hams measure 3rd order IM by injecting two
> relatively close-spaced signals into the rx and raising the level until an
> inband distortion product shows up. Typically it's two signals 20 kHz on
> 20 meters. 

With practical front end tuned circuits testing at 20 kcs spacing on 
20M tests only the mixer because the practical Q's give you no 
help rejecting the unwanted signals.   On 80M, both the front end 
coils and the mixer are tested.   Both tests are of interest.

That actually works out pretty well because there's usually a much 
bigger problem with IMD on 80M than on 20M. 

On the HBR-4 project, I hope to get 30 and 20M working today.   
The Butler oscillator is actually working reasonably well now, 
though I am going to go crazy with the retuning all the crystals 
every time I move that trimmer board to add another band or two.  
Those 50 mmf trimmers tune so sharply on the high bands that you 
really have to hunt for the crystal frequency.

An additional problem is tuning drift, probably due to heating of the 
toroid.  It usually takes a couple of retunings after each change to 
find the point at which the CO will *keep* working as the set warms 
up.  There are higher stability cores available; I may have to look 
into that.   Or I can just use a slug tuned coil with a VHF core -- 
that's probably simpler.

Walt 
KJ4KV
From windy10605 at juno.com  Wed Aug 18 11:21:29 2004
From: windy10605 at juno.com (windy10605@juno.com)
Date: Wed Aug 18 11:27:23 2004
Subject: [HBR] Receivers
Message-ID: <20040818.102129.428.0.windy10605@juno.com>

I have really enjoyed the interchange going on. Great discussion. 

Just a little different thought flow................

I like experimenting with and building all the analog tube rigs, but with
the problems associated with heterodynes, and the advent of super stable
PLL oscillators, isn't there a possibility of applying direct conversion
here, regeneration even ? I know regens are usually poo-poo'd. I would
continue to focus on a very low noise highly tuned LC and tube frontend
for sensitivity and selectivity with a focus on high Q. Somewhat like a
tunable Q multiplier frontend ..... I guess that's basically what a regen
is in part. So what are the pitfalls of regeneration in addition to lack
of stability and how do you solve them ? Maybe, back off on the
regeneration and add the best solid state has to offer for the non signal
source osc, and finish out with tubes for the audio, ? 

73 Kees K5BCQ
From N2EY at aol.com  Wed Aug 18 12:07:36 2004
From: N2EY at aol.com (N2EY@aol.com)
Date: Wed Aug 18 12:12:22 2004
Subject: [HBR] Re: W1KLK receiver
Message-ID: <0E100702.02BE31C4.00002CAA@aol.com>

In a message dated 8/18/2004 10:26:21 AM Eastern Daylight Time, waltah@earthlink.net writes:

>Jim said:
>> Agreed but I read the article a bit differently.
>> 
>> I think you could get adequate image rejection without all those
>> tuned circuits. What 'KLK wanted was not just image rejection but
>> rejection of strong out-of-band signals - meaning anything more
>> than a few dozen kHz away from the desired signals. If the signals
>> don't reach the mixer, it doesn't have to deal with them. 
>
>Yep. ? For 80M, however, he probably could have used the 7360 
>mixer 'barefoot' and done even better; there's no serious problem 
>coupling two or three tuned circuits without a tube between if you 
>are only covering 500 kcs at 80M. 

I'm not sure about that. He'd still need 4 tuned circuits between antenna and 7360 grid to get the kind of RF selectivity he wanted.?Aligning such a monster would be difficult; with the quiet, low-gain GG 7044 he gets isolation between the two doubletuners. 

I have seen exactly one 7044 in over 30 years of looking. I bought it. Possible subs are 5687 and 2C51. Note the unusual basing of these tubes; they are tailormade for pushpull or GG circuits, unlike most dualtriodes.
>
>I don't know what the ultimate sensitivity of the beam tubes is as 
>mixers but it's pretty good. ? I've got 0.25 uV on 40 meters with no 
>RF stage and two tuned circuits preceding the mixer. ?

The SquiresSanders article says they got less than 5 dB noise figure from a 7360 mixer - on 10 meters!

For a single 
>band receiver you could use a push-pull 6J6 oscillator, with 12AT7 
>cascode buffer if needed (probably not) -- the design should be a 
>cinch.

You need a pushpull tuning cap, too.

SS used a balanced transformer to drive the 7360 deflectors. With modern toroids and a buffer stage, a bifilar link might be the way to go. Or a phase splitter.

>With just one oscillator he wouldn't have the problems I 
>have with spurious responses. ?

G3PDM (or was it G3DPM) has a design in one of the RSGB handbooks of that era. Dualtuner straight into a 7360, xtal filter at 1680 kHz, etc. His solution to the LO problem was interesting:

The actual LO is a dualtriode balanced oscillator, directly driving the 7360 deflectors. It is varactor tuned.

He has a very stable VFO which is premixed with the output of an xtal het osc. This output is compared with a sample of the balanced LO, and the error signal drives the varactors in PLL fashion.

No digital stuff - all analog, mostly hollow but with a few sandstate devices like a UJT that sweeps the LO if phaselock is lost.

No specs on phase noise but pretty slick for ~1968, doncha think?
>
>The purest would probably use both 'top' coupling for the front end 
>coils (with a small cap between the tuned circuits) and 'bottom' 
>(with a shared small coil at the bottom so the gain could be leveled 
>across the band.

It'd be a mess to align, tho.

 ? In a bandswitched receiver you run out of space 
>pretty fast with so many parts but for a single band it's surely not a 
>problem.

Bigger chassis. If we want small we can just go buy a rig. 

About 1964, W9BRD's DX column carried a tale where he talked about miniaturization. His criteria became whether or not the shack cat (Madame Mu, a Siamese, though her name is done with the Greek letter) could perch atop it. 
>
>An interesting design would be plug in front ends, with different 
>VFOs according to the band. ?You could even use different 1st IFs 
>and convert to a common IF to do most of the amplification in the 
>mainframe. ? Four tubes, maybe, in the plug-in unit and the rest on 
>the mainframe. 

It's been done. The metalwork is the real killer. Turrets are one solution.

One idea I've toyed with is to have a common VFO/IF, but separate frontends and matching transmitters for each band. 
? 
In QST for 1971, a 160-6 meter transceiver was described (the ATR-166). Used the Heath SB het scheme, 898 dial, some really good ideas. Had features you could not get in an SB line. All in one box. You changed bands by swapping modules - RF amplifier, driver, heterodyne oscillator, final tank. It was the inspiration for the Southgate Type 5 and Type 6 transceivers, one version of which still exists. 

>
>> If I understand the process, we hams measure 3rd order IM by injecting two
>> relatively close-spaced signals into the rx and raising the level until an
>> inband distortion product shows up. Typically it's two signals 20 kHz on
>> 20 meters. 
>
>With practical front end tuned circuits testing at 20 kcs spacing on 
>20M tests only the mixer because the practical Q's give you no 
>help rejecting the unwanted signals. ? On 80M, both the front end 
>coils and the mixer are tested. ? Both tests are of interest.
>
>That actually works out pretty well because there's usually a much 
>bigger problem with IMD on 80M than on 20M. 

My point is that many rxs inhale so many MHz that IM troubles may be caused by signals hundreds of kHz away. 
>
>On the HBR-4 project, I hope to get 30 and 20M working today. ? 
>The Butler oscillator is actually working reasonably well now, 
>though I am going to go crazy with the retuning all the crystals 
>every time I move that trimmer board to add another band or two. ?
>Those 50 mmf trimmers tune so sharply on the high bands that you 
>really have to hunt for the crystal frequency.

I just yanked plates off them...
>
>An additional problem is tuning drift, probably due to heating of the 
>toroid. ?It usually takes a couple of retunings after each change to 
>find the point at which the CO will *keep* working as the set warms 
>up. ?There are higher stability cores available; I may have to look 
>into that. ? Or I can just use a slug tuned coil with a VHF core -- 
>that's probably simpler.

That's a lot of trouble for a crystal oscillator!

I shall dig up one of my old flyers from C-W Crystals 

(moment of silence in memory of a friend I never met)

which has most of the circuits I use, and get that info to you.

73 de Jim, N2EY

From waltah at earthlink.net  Wed Aug 18 20:57:37 2004
From: waltah at earthlink.net (waltah@earthlink.net)
Date: Wed Aug 18 21:11:46 2004
Subject: [HBR] Another Receiver Project -- HBR-4, Part 11
In-Reply-To: <41223F43.15344.1D54369@localhost>
References: <12f.48d6837e.2e510ba4@aol.com>
Message-ID: <4123C2C1.23135.ACF845@localhost>

Finally got around to sensitivity checks with the increased mixer 
drive level.   Sensitivity is signal for 6db S+N/N.

80M (3800) S9 = 60 uV   Sens = 0.8 uV 

40M (7300) S9 = 15 uV   Sens = 0.25 uV

There's certainly no need for an RF stage.   Of course it remains to 
be seen how serious the problem of in-band spurious signals will 
be -- there's at least one big one in each of these two bands but I 
have given that problem no attention yet.

The 30 and 20 meter bands are now working.  The only excitement 
there was the discovery that on 20 you don't need much coupling 
at all between the input tuned circuits -- anything over 1 mmf led to 
the classical double peak of overcoupled circuits.   There's 
substantial coupling through stray capacitance between switch 
decks and the trimmer wiring.

With WWV (10 Mcs) available I found that the 100 kcs calibrator 
needs a larger fixed cap to come on frequency.

I have a somewhat long wire (~3 wavelengths?) for 20M pointed 
toward Europe; there are Europeans all over the dial.  

I said:
> Those 50 mmf trimmers tune so sharply on the high bands that 
> you really have to hunt for the crystal frequency.  

Jim:
> I just yanked plates off them...

These are ceramic rotaries, 7 mm in diameter.   I used the crystal 
and RF trimmer assemblies from the FT-101 and mounted seven of 
those little trimmers on a scrap of GFRP for the premixer plate.   
It's not easy even to extract these trimmers from the boards -- 
there are always one or more bad ones to change and it is one of 
my least favorite jobs.   

I'm pretty sure the FT-101E used some smaller ones; if the tuning 
rate is a serious enough problem I probably have some spares I 
can liberate.

> G3PDM (or was it G3DPM) has a design in one of the RSGB handbooks
> of that era. Dualtuner straight into a 7360, xtal filter at 1680
> kHz, etc. His solution to the LO problem was interesting: 

> The actual LO is a dualtriode balanced oscillator, directly
> driving the 7360 deflectors. It is varactor tuned. 

G3PDM was the builder and it's a very interesting approach indeed; 
I'm glad you didn't mention it before I got well into this project.   The 
essential idea is that you build a bandswitching LO tuned within 
each band by a varactor and lock that to a synthesized signal.   
That keeps the impurities in the synthesized signal out of the 
received signal path and since the synthesized signal doesn't have 
to be large amplitude, they're going to be easier to contain, 
anyway.  With a good quality oscillator, phase noise should be 
negligible.   It takes maybe three or four more tubes -- he did it with 
solid state devices though.  

Actually I think I'd have had the sense to stay away from it for now. 
Direct synthesis is simpler and there's plenty that's brand new to 
me, even as the project is.

The hardest radio project I ever tackled was putting an ARC-38A 
aircraft transceiver back on the air.   The ARC-38 was a Collins AM 
set, frequency locked on a whole bunch of channels 2-24 Mcs as I 
recall.   RCA got the contract to convert a flock of them to SSB; 
thus was born the phase-locked ARC-38A.   Fifty-some tubes, 
mostly subminiature.   It took a few weeks of troubleshooting but I 
got it working, +/- problems caused by newly dead crystals.   And 
the nastiest problems were in the PLL circuit -- most of them being 
(as in all RCA military sets of my experience) due to lousy RCA 
quality control.   

The HBR-4 is a lot more fun.   Tomorrow I need to return to the 
balance of the mixer stage; I'm certain I don't have that right.   

Walt
KJ4KV


From waltah at earthlink.net  Thu Aug 19 22:04:14 2004
From: waltah at earthlink.net (waltah@earthlink.net)
Date: Thu Aug 19 22:18:27 2004
Subject: [HBR] Receivers
In-Reply-To: <20040818.102129.428.0.windy10605@juno.com>
Message-ID: <412523DE.16086.7295C5@localhost>

Kees wrote:

> I have really enjoyed the interchange going on. Great discussion. 

Can't tell you how much I enjoy having a few kindred spirits to 
discuss this stuff with ... if anyone else is doing this I don't know 
who or where.

> Just a little different thought flow................
> 
> I like experimenting with and building all the analog tube rigs, but with
> the problems associated with heterodynes, and the advent of super stable
> PLL oscillators, isn't there a possibility of applying direct conversion
> here, regeneration even ? I know regens are usually poo-poo'd. 

I don't think they should be poo-poo'd.   People *do* still build them 
-- a lot more of them than HBR-scale superhets.

> I would continue to focus on a very low noise highly tuned LC and
> tube frontend for sensitivity and selectivity with a focus on high
> Q. Somewhat like a tunable Q multiplier frontend ..... I guess
> that's basically what a regen is in part. 

Yep, a regen is a Q-multiplier that has enough more feedback and 
is so configued that it gets out of the linear range and become a 
detector.   

> So what are the pitfalls of regeneration in addition to lack
> of stability and how do you solve them ? Maybe, back off on the
> regeneration and add the best solid state has to offer for the non signal
> source osc, and finish out with tubes for the audio, ? 

Bite yo' tongue ... solid state indeed ... Hi.

Although people do still build regens, I'm not sure many of them 
have thought through the theory.    The approaches seem to divide 
into "I built an exact replica of this 193X regenerative set described 
in ..." and "I built this regen set that uses modern tubes and has 
the following features not found in early sets."   

Nor am I really sufficently theoretical to do the subject justice.   
But when did that ever stop me from trying?

Stability breaks into two parts:  *frequency* stability, meaning that 
the set will stay correctly tuned to the selected station -- I don't 
immediately see why it wouldn't be possible to do that with SSB, 
since we build VFOs at up to 10 Mcs that do it.

Frequency stability is exactly the same game as for a VFO and 
that game is familar.   Use a high gain tube and decouple as much 
as possible from the tank circuit.   Use stable components and 
keep heat away from them, so far as possible.   Put the tank 
circuit in a box with the tube outside and use tiny wire to connect 
the two, taking care that the tiny leads don't flop around.   

I would certainly use a good dial mechanism; bandspread 
requirements for tuning SSB are the same regardless of the 
detector type.

Then there's *amplitude* stability -- when regeneration control is 
adjusted, it *stays* adjusted, regardless of tube parameter 
variations and signal strength.   I have less understanding of the 
issues there.   I'd certainly want to try one of the variable-mu tubes 
like the 6ES8 or 6EH7 but whether that would really be better or 
something like a 6GK5 would be best, (high gain VHF TV RF tube) 
I don't know.   I've never heard of an attempt to discuss the 
requirements for the ideal regenerative detector in terms that could 
be translated to a tube type.

I'd start with a 6ES8 push-pull oscillator set up to oscillate at pretty 
high grid leak bias (small plate current) and reduce the voltage until 
it went out of oscillation.   That *should* (says the guy who never 
built one) give you a regenerative plate detector.   Plate resistor 
100k or up.   Then an audio amp after that.  

An interesting variation would be a crystal controlled converter 
ahead of the detector; in effect the regen detector would be a 
tunable IF.   The converter stage would get rid of antenna effects 
and the consequences of trying to tune more than one band in the 
detector -- bound to be worse than a multiband VFO.

Doing it this way you could apply audio-derived AGC to the 
converter stage.

I believe the Handbooks about 1965 had a three or four tube 
receiver consisting of a tunable converter stage and a fixed-tuned 
regenerative detector.   Was this the Super Simple-X receiver?   
And there was an article published in CQ sometime in the 60's I 
think about a crystal controlled regenerative detector.

Walt 
KJ4KV
From waltah at earthlink.net  Fri Aug 20 16:16:22 2004
From: waltah at earthlink.net (waltah@earthlink.net)
Date: Fri Aug 20 16:30:41 2004
Subject: [HBR] Another Receiver Project -- HBR-4, Part 12
In-Reply-To: <4123C2C1.23135.ACF845@localhost>
References: <41223F43.15344.1D54369@localhost>
Message-ID: <412623D6.6444.71B407@localhost>

In order to do a decent job balancing the mixer, I bifilar-wound the 
plate transformer plate halves, then wound a secondary (to drive 
the crystal filter) over them.   I had the differential trimmer cap from 
the FT-101 VFO (couldn't use it for a push-pull VFO) so I put that in 
for adjusting the RF balance and I increased the range of the DC 
deflection plate balance by using a larger pot.  

(Dumb-de-dumb-dumb -- I forgot to put a piece of paper between 
the primary and secondary and there's 130 volts difference there ... 
Two hours work to rebuild that transformer if the insulation on my 
Radio Shark enameled wire isn't quite perfect.   But okay so far.  
The decoupling resistor for the stage is basically a 30 mA fuse, so 
no great damage will be done.) 

The test of mixer balance is what happens when you feed a strong 
9 Mcs signal in at the antenna jack.  Since that signal isn't 
converted, it isn't push pull at the mixer plates -- it's the same at 
both plates and should cancel out in the plate transformer.   I really 
didn't have that before.

Got it now though -- what a difference.   Setting the bandswitch to 
30 meters and running the preselector down to the lowest 
frequency, I can get the 90th harmonic of the calibrator at S9+20 if 
the mixer is way out of balance.   Swing the pot around and 
suddenly the signal vanishes.   The first time I hit the right setting, I 
thought I had shorted something.   

The balance circuit is:  100k resistors from each deflection plate to 
ground.   470k resistors from the deflection plates to the ends of a 
1M pot.  Rotating contact of the pot to -70VDC bias.   With the pot 
centered you get a bit less than -7V bias on each plate.   Balance 
for this tube occurs with a difference of about 3 volts between the 
two -- a surprisingly large difference.   Checking eight 6JH8's in that 
socket I found that the differences went as high as 3.5 volts with 
only three under 1 volt.   One, however, was 0.085V!

The RF balance differential cap also has an effect but winds up 
near center position -- no more correction than you'd expect from 
parts tolerances, interelectrode capacitances, and wiring 
differences.

I need a smaller value pot -- the 1Meg pot can't be precisely 
adjusted.   500k or possibly 250k should do it.  This is a 1/2" 
diameter pot with a 1/4" bushing, not the most popular item.   My 
stock skips from 50k to 1Meg ... but I have a few more places to 
look.  

I also need to select a tube that balances with a smaller difference. 
250k will only give a 25% difference -- less than 2 volts.   

This would actually be a good place for a multi-turn pot since you 
need both considerable range and accurate setting.   I might have 
one that would work.   Also I could put the pot on the ground side 
rather than the bias voltage side -- that would let me use lower 
range pots.   Yeah, there's an answer in there somewhere.

Just as we all discovered when sheet beam tubes were popular as 
balanced modulators in ham SSB transmitters, the null drifts 
considerably.   It looks to me like you can count on 30 to 40 db, 
but the 60 db I've seen quoted in a few places is only while you 
have the screwdriver in your hand.

The main importance of good mixer balance is rejecting signals (of 
all kinds) at the IF coming in via the antenna.   30+ db is a great 
addition to the rejection due to the two front end tuned circuits.   
Adding a trap is certainly possible as the final step.

Walt
KJ4KV
From waltah at earthlink.net  Fri Aug 27 19:53:32 2004
From: waltah at earthlink.net (waltah@earthlink.net)
Date: Fri Aug 27 20:09:14 2004
Subject: [HBR] Another Receiver Project -- HBR-4, Part 13
In-Reply-To: <412623D6.6444.71B407@localhost>
References: <4123C2C1.23135.ACF845@localhost>
Message-ID: <412F913C.27582.14771A9@localhost>

Heading into the home stretch, I think ... Now working on the 
spurious responses.   

There is about one serious spur per band, S9 to S9+20 strength on 
the bands 80 through 20 meters.    Some things that I have 
tinkered with are:

A.   Increasing the oscillator cathode resistor.   This seems to 
help, presumably by reducing the osc. grid current and hence 
distortion.  

B.  Reducing the VFO output.   This helps but there's a trade-off 
with sensitivity.  

C.  A 9 Mcs trap in the premixer plate circuit.   The strong spurs all 
seem to leave the premixer at 9 Mcs so this helps considerably.   
It is complicated by the push-pull circuitry and there's interaction 
between the trap and the tuning of the premixer plate.

A possibility that I haven't tried is a high pass filter between the 
premixer and the mixer, cutoff above 9 Mcs but below 16 Mcs.   
This wouldn't be as effective as a 9 Mcs trap because the strong 
spurs all involve 9 Mcs.  

A low pass filter at the output of the VFO to the premixer should be 
helpful since all significant spurs involve a 3rd harmonic or higher 
and much of the harmonic generation is probably in the oscillator.  

Further reducing the oscillator grid current should help the spurs 
involving an even harmonic of the VFO.   The odd VFO harmonics 
are more likely the result of imbalance in the premixer with VFO 
imbalance a secondary issue.

What about jiggering the VFO and crystal frequencies slightly to 
(possibly) move the spurs out of band?  The worse ones on the first 
four bands are:

(dial freq -- strength -- multiple x osc. freq = freq - xtal = 9 Mcs)

3600 -- S9+20 -- 5 x 5.4 -> 27 - 18 = 9 Mcs.

7417 -- S9 -- 6 x 5.083 -> 30.5 - 21.5 = 9 Mcs

10,334 -- S9+20 -- 3 x 5.166 -> 15.5 - 24.5 = 9 Mcs

14,000 -- S5 -- 12 x 5.5 -> 66 - 2 x 28.5 = 9 Mcs

14,143 -- S9 -- 7 x 5.357 -> 37.5 - 28.5 = 9 Mcs

14,167 -- S9 --  9 x 5.333 -> 48 - 2 x 28.5 = 9 Mcs

The rest are all at the S0 level -- you can hear them with no 
antenna connected but any significant noise or signal would cover 
them up.

Note that those that are in band are near the low end.   This 
suggests tweeking the VFO and crystal frequencies slightly 
downward.   

For example moving the VFO range down 125 kcs (4.875 - 5.375) 
and the crystals down by the same amount gives us:

(dial freq -- multiple x osc. freq -> freq - xtal = 9 Mcs

3500 -- 5 x 5.375 -> 26.875 - 17.875 = 9 Mcs

And thencely:

7312 -- 6 x 5.063 -> 30.375 - 21.375 = 9 Mcs

10,250 -- 3 x 5.125 -> 15.375 - 24.375 = 9 Mcs

13,896 -- 12 x 5.5 -> 65.75 - 2 x 28.375 = 9 Mcs

14,036 -- 7 x 5.339 -> 37.375 - 28.375 = 9 Mcs

14,069 -- 9 x 5.306 -> 47.75 - 2 x 28.375 = 9 Mcs

That's better but not what you'd call a cure, especially since there 
are also spurs on the higher bands.

It seems that the first thing is to optimize the VFO operating 
conditions.  It should be as close to class 'A' operation as possible 
because grid current drawn on positive peaks causes even-
harmonic distortion of the waveform.  I'll look at the oscillator coil 
and see if the Q can be increased; unfortunately that would require 
a heavier gauge wire and there probably isn't space on the form. 

With an oscillator signal in the 10V p-p range and spurs of perhaps 
100 uV, it doesn't take a lot of distortion!  

Second to that, the premixer needs to be accurately balanced, with 
the adjustment made while watching an odd-harmonic spur.   
Some further improvement may be gotten by selecting the 
oscillator tube for minimum odd harmonic output -- the halves are 
never perfectly balanced.

Then start with the traps and filters.  More to come, obviously.

Walt
KJ4KV


