[Drake] Re: Questions from a new ham (even longer, I am afraid!)

[Barry L. Ornitz]

Jeff Anderson asked the list some insightful questions for 
a relatively new ham.  I'll try to answer those that I 
can.  Sorry if my reply is rather long.  I have tried to 
cut and paste on these to avoid quoting his entire 
message.  Those that blindly quote entire earlier messages 
are, in my opinion, lazy and impolite and they waste 
considerable bandwidth that Al has to pay for.

> My station consists of a TR-3 (a hamfest unit that 
> required lots of work) with a D-104 mic, an L network 
> tuner that I built (has no tuning indicator), and a G5RV 
> antenna that I recently put up.  I also have an MFJ 259B 
> antenna analyzer, the W-4 watt meter, and some no-name 
> inline SWR meter that I can use to help me get things set 
> up.

An excellent setup.
 
> 1.  Must the antenna be accurately tuned before tune-up 
> of the TR-3 is attempted?

Trick question.  The tuner takes care of a non-resonant 
antenna to present a low VSWR to the transmitter.  But I 
believe the question is whether the tuner must be adjusted 
before the transmitter is activated.  The answer here is 
generally yes but with some caveats.  Read on.

> 2.  Will the tuning of the antenna effect the tuning of 
> the transmitter?

Again I assume this means the settings of the tuner 
affecting the tuning of the transmitter.  Yes.  The tuner 
is merely a device to transform the impedance seen on its 
output side to another impedance on its input side.  The 
tuner settings change this transformation making the 
impedance the transmitter sees change, necessitating the 
proper adjustment of the transmitter tuning network.

> Using the MFJ analyzer, at the point where the feedline 
> connects to the TR-3, I have verified that the tuner will 
> match the antenna with an SWR of less than 2:1 on all 
> bands.

This is quite adequate for the TR-3.  Like most vacuum tube 
transmitters with an adjustable output network, the TR-3 
can generally handle an even higher VSWR without damage.
 
> 3.  Is the use of an inline SWR meter the proper method 
> to ensure proper antenna tuner adjustment in a normal 
> station setup?

This is one way.  Likewise the wattmeter can be used, as 
can the MFJ analyzer.  The procedure is slightly different 
with each instrument however.  Having the analyzer allows 
for adjusting the tuner without putting a signal on the air 
and without the risk of attempting to transmit into high 
VSWR.

> 4.  The W-4 watt meter will display forward and reverse 
> power, but it seems to require the use of a lot of 
> forward power to get usable meter movement when viewing 
> reverse power.  Is this not the proper device for antenna 
> tuner adjustment?

A directional wattmeter can be used as an indicator of 
VSWR.  The W-4 originally came with a nomograph for 
converting readings into VSWR.  You can easily do this with 
a pocket calculator too (and I used a slide rule back in 
the good ol' days).  However there is no need to calculate 
the VSWR while adjusting the antenna tuner.  Merely adjust 
the tuner for minimum  reflected power.  The sensitivity of 
the wattmeter is some what deceiving.  For example if you 
have 100 watts of forward power and 10 watts of reflected 
power, the VSWR is:

    VSWR =  (SQRT(PF/PR) + 1)/(SQRT(PF/PR) - 1) 

         = (SQRT(10) + 1)/(SQRT(10) - 1) 

         = (3.162 +1)/(3.162 - 1)

         = 1.925

where:  PF = forward power, 
        PR = reverse power, and 
        SQRT is square root.  

If you do the same calculations with 250 watts forward and 
1 watt reflected, the VSWR is 1.135.  If you have much 
reflected power at all, you have a mismatch.

> 5.  Is there any way to verify proper adjustment of the 
> antenna tuner using the plate current meter on the TR-3?

Not really.  With lots of back-and-forth adjustments of the 
TR-3 controls and the antenna tuner adjustments, you can 
reach a point where the TR-3 will operate, but operation 
may not be optimum.  What you would be doing is hitting a 
combination where the output impedance to the transmitter 
falls within the TR-3's adjustment range.  For best 
operation (efficiency and harmonic suppression), it would 
be better if the impedance seen by the TR-3 is close to 50 
ohms.

> With regard to TR-3 tune up, the thing I have the most 
> concern about is:
> 6.  How fragile are the final tubes????

The TR-3 (and most other Drake tube transmitters) use 
television sweep tubes in the final amplifier.  They have a 
limited plate dissipation.  However they can stand some 
abuse (excess plate dissipation) for short periods of 
time.  In their day, they were less expensive than other 
transmitting tubes of higher plate dissipation.  Today, 
they are somewhat difficult to find, especially in matched 
sets (and they _DO_ need to be matched).  So while I would 
not consider them particularly fragile, I would still try 
to avoid abusing them to prolong their life.

> The manual states not to allow more than .1 amps of plate 
> current for more than 30 seconds or so, or the finals 
> could be damaged.  Is this due to the high SWR that could 
> be present during tune up?  I don't want to damage the
> finals (they did cost a lot), but 30 seconds isn't very 
> long to tweak all the knobs that need to be tweaked.

During tune-up of the transmitter (independent of the 
antenna tuner), the tubes can see very high plate 
dissipation until the rig's internal impedance matching 
network is adjusted.  Hence the reason for tuning quickly.  
Not all the adjustments on the transmitter need to be 
tweaked during tune-up, however.  The RF-Tune adjust can be 
approximately peaked by adjusting for maximum signal during 
reception.  The two critical adjustments are the Plate and 
Load controls.  Adjust these first, then peak the RF-Tune 
control.  This should take only a few seconds, rarely 
longer than 10 seconds.

This assumes, of course, that the transmitter is working 
into the proper impedance load.  This can be a dummy load, 
or a properly adjusted antenna tuner.

> The TR-3 tune-up procedure calls for dipping the plate 
> current, and maintaining the dip while adjusting the LOAD 
> control.
> 7.  What does it mean if I can't find the dip in the 
> plate current, or if the dip seems to be all the way to 
> one end of the PLATE control range?

This usually means that the transmitter load is out of the
adjustment range for an impedance match with the internal 
matching network.  This should NEVER happen if the TR-3 is 
loaded into a 50 ohm dummy load.

> 8.  Do the proper adjustments of the PLATE and LOAD 
> controls correspond to a peak power out indication on the 
> W-4 watt meter?

Yes, if the final amplifier is neutralized properly, plate 
current dip will correspond to maximum forward output 
power.  In fact, this is the method used to determine if 
the final needs neutralization.
 
> After all this, it seems quite easy to get LOTS of output 
> power (as displayed on the W-4 watt meter) while 
> performing the tune-up in X-CW mode as specified.  But 
> after tune-up is complete, and the function switch is
> returned to the SSB position, the watt meter displays 
> very little output, the plate current meter moves very 
> little, and the S meter doesn't move at all when speaking 
> into the microphone.  If the XMTR GAIN control is 
> increased, I can get higher output indications while in 
> SSB mode, and get the s-meter to move.  I believe that 
> this indicates that the transmit AGC is working, and that 
> XMTR GAIN is adjusted for maximum output.  The output 
> meter still doesn't indicate very much while set to 
> operate SSB.

With no audio while transmitting in the SSB position, there 
should be _NO_ RF output.  The presence of any indicates 
that the carrier balance needs to be adjusted.   Turning up 
the microphone gain applies audio and you should see output 
as you speak.  The W-4 wattmeter has considerable damping 
so it indicates average RF output.  But remember that the 
peak to average power ratio of speech is quite high.  Thus 
you may be getting peak power on voice peaks of several 
hundred watts while the wattmeter indicates only a few tens 
of watts.  Do not adjust the XMTR GAIN control for maximum 
output or you will seriously distort your output signal 
(called flat-topping).  Your instruction manual will give 
you a procedure for the proper setting.  If you have an 
oscilloscope, the setting can be determined much more 
accurately.

> 9.  If the plate current meter displays reasonable plate 
> current while in the X-CW mode, is this an indication of 
> proper operation of the finals?  What are the indications 
> of weak finals?

Yes.  Into a 50 ohm dummy load (or your properly adjusted 
tuner), on CW you should be able to get at least about 140 
to 150 watts of output if the tubes are good.  You may see 
a little less on 10 meters.  Weak finals show up as reduced 
output power.  The higher bands, 10 or 15 meters, generally 
show this loss first. 

> Well, thanks for reading this far.  I will appreciate any 
> help you can give me.  I would like to make my first QSO 
> some time in the not too distant future.  If I can gain 
> confidence that my station is configured and operating 
> properly,  I should be on the air soon. 

> It would probably be better to reply off the list.  The 
> fewer times this novel travels around the world, the 
> better.

Good luck.  I am sure you will have lots of fun with the 
TR-3.  I answered here because your questions were well 
thought-out and because others may benefit from the answers 
too.

I would like to go back to my earlier comments about the 
antenna tuner and the MFJ analyzer...

Most modern solid-state rigs have broadband outputs that 
are designed for 50 ohms output impedance.  This is not 
adjustable.  If the output impedance seen by these rigs is 
not within the 2:1 VSWR circle on a Smith Chart, these rigs 
generally reduce their output power to protect the 
transistors from excess dissipation.  Tuner adjustment is 
usually pretty critical with these rigs.

The older tube rigs were considerably different.  The early 
rigs, mainly those for AM and CW, usually had output 
networks capable of matching a wide range of impedances.  
You could use any reasonable antenna without a tuner as 
these rigs could handle a VSWR of as high as 5:1 without 
problems.  Rigs like the venerable old Johnson's and even my 
ancient Heath DX-35 could load up the proverbial rusty 
screen door with the one-eyed tomcat climbing it!

The later tube rigs, like the SSB/CW rigs such as the TR-3, 
still had adjustable output networks.  However, their 
matching range was generally reduced.  They naturally 
preferred a nice 50 ohm impedance, but their PLATE (TUNE) 
and LOAD adjustments allowed for a "reasonable" VSWR with 
only a minimal loss in efficiency.  Thus if your VSWR was 
within 2 or 3 to one, you did not worry.

This is the reason I said earlier than adjusting the 
antenna tuner to get a perfect 1:1 match is not necessary 
with these tube rigs.  Just get it close.  The internal 
adjustments of these rigs can then do the rest of the 
matching needed.

I do not recall seeing that you had a dummy load 
available.  These are nice to have and you might consider 
looking for one at future hamfests.  With one, you can 
adjust the TR-3 into 50 ohms and do most adjustments 
without transmitting a signal to interfere with others on 
the bands.  They make bench testing easier too.

But since you have the MFJ analyzer, you can use it as an 
alternate method of adjusting the impedance matching.  
Using the analyzer, determine the settings needed by the 
antenna tuner to provide a 50 ohm output impedance for the 
range of frequencies you transmit.  Make a table of these 
settings.  Then when you are ready to operate on a given 
frequency, pick the tuner settings from your table and dial 
them into your tuner.  Then adjust the TR-3 PLATE and LOAD 
for maximum signal into the tuner.

You may find that the tuner settings do not vary much over 
a given band (especially the higher frequency ones).  In 
this case, determine the tuner settings for the middle of 
the band.  Then while not adjusting these settings, use the 
analyzer to determine the VSWR at the band edges.  If this 
is less than 2:1, just use these settings for the entire 
band.  The TR-3 will be able to make the necessary matching 
to handle this.  This will likely not work on the lower 
frequency bands like 80 meters, but you may find settings 
suitable for the phone and CW ends of the bands.

Using this procedure, you will find that far fewer 
adjustments are needed.  You have to do the PLATE and LOAD 
settings of the TR-3 anyway, so why not use them to 
simplify your tuning?

> 73,
> Jeff Anderson  KD7PAW

Again, good luck.  May you and your TR-3 have many years of 
fun together.  My Drake twins (T-4x and R-4a) have been 
with me for 37 years.They are still my favorites.

        73,  Dr. Barry L. Ornitz     WA4VZQ     ornitz@tricon.net