[HBR] 160 Meter Coil Data

[Hopperdhh at aol.com]

Hi Walt and all,

Not sure if you read my earlier post, since you didn't address it.  But, I 
spent a few hours doing some calculations to design some 160 M coils yesterday.

It is not necessary to use 3 point tracking to cover just a ham band.  
Seventy cps tracking is kind of ridiculous when the bandwidth of the front end 
circuits is probably more than 1000 times that great.  The coil design that I show 
below (and posted earlier) has a tracking error of 4.5 KHz.  This is called 2 
point tracking.  It is usually just set at each end of the band, like Ted's 
alignment procedure.

As far as tapping the coils, you will notice that the latest HBR 80 M coils 
are tapped 1/4 turn from the top which is basically no tap at all.  The coils 
below could still be adjusted by Ted's spacing method.  I didn't include that 
in this preliminary design.  If someone wants to refine my design, I certainly 
have no problem with that.  Keep us posted.  In fact, no. 28 wire may be 
preferred since it would take up less space leaving room for the APC trimmer at the 
top of the form.  The Q would drop some, but it is really plenty high with 
no. 26 -- about 175.

I used 1.79 to 2.01 MHz and a cap range of 6.6 to 23 pF (Miller Catalog No. 
1461-BS).  Try these values in the tracking program and see if the L's and C's 
that I derived aren't pretty close.

Here is a repeat of my results:


L1 and L2 (Antenna and RF):
99.74 uH with parallel C of 56.26 pF.

Wind 69 1/2 turns of no. 26 on the 1 1/4 inch polystyrene forms to cover the 
entire 160 M band.  No tap, connect pins 3 and 4 together inside the coil 
form.  
You will need a total of about 56 pF across the coil, so a 39 pF fixed + a 50 
pF variable should do it.  I would suggest a modern sub-miniature variable 
placed way down in the form as a practical alternative to the APC which would 
probably spoil the coil's Q.  In keeping with Ted's ratios, try 23 turns for 
the 
primaries.


L3 (Oscillator):
15.74 uH with parallel C of 116.2 pF.

Wind 19 1/2 turns of no. 26.  No tap -- same as above.  You will need a total 
of 
about 116 pF across the coil.  Use 75 pF silver mica + 50 pF variable as 
above. 
Feedback would take about 13 turns, again keeping Ted's ratio.

I haven't tried these since I don't at the present time have an HBR, so there 
are no guarantees here.  Strictly a paper design with some experiments on the 
Q-Meter.  I noticed that only .001 uF capacitance is used some places in the 
front end and this may be a little low for 1.8 MHz.  (Seems low for 3.5 MHz to 
me!)  I will parallel them with a .01 when I build my receiver, if necessary.

Regards,

Dan Hopper
K9WEK


In a message dated 12/27/2006 3:43:09 PM Eastern Standard Time, 
waltah at ntelos.net writes:
160 meter coils can certainly be wound for the HBR series: the 
percentage coverage is less than for 80 -- that is, 200 kcs from 
1800-2000 kcs vs. 500 from 3500-4000.

With stray capacitance typically running ~10-15 mmf I'd guess you could 
get a tuning range as great as 50% in the HF range with some sacrifice 
of performance.    Not the BC band and not even the range of 800-1500 
Kcs, because the stray capacitance of a coil that would cover such a 
range with such a small cap would further restrict the tuning range.

There are superhet tracking calculators on the web.  Google 
'superheterodyne tracking.' One that seems to work okay is at:

http://ironbark.bendigo.latrobe.edu.au/~rice/superhet.js/superhet.html

For the case in question -- assuming tuning 1.8-2.0 Mcs with a cap range 
of 27 to 3 mmf and NO coil taps -- the program yields the answers:

Aerial circuit values       Oscillator values

Inductor        61.89 uH    Inductor        10.82 uH
Trimmer         99.32 pF    Trimmer        177.65 pF
                             Padder         311.35 pF

These values appear to be a correct solution.

(There are an infinite number of correct solutions and you get to pick 
one depending on your view of what is best -- generally how you look at 
minimizing the tracking error.  This program appears to pick the 
solution that minimizes the maximum error, which for this tuning cap and 
frequency range is claimed to be under 70 cps.)

The term 'padder' is conventionally used to refer to a cap connected in 
series between the tuning cap and the coil, thus serving to reduce the 
effective maximum capacitance and set the minimum frequency for that 
circuit.  The 'trimmer' is the shunt cap. and will set the maximum 
frequency.  With the oscillator above the signal frequency and a tuning 
cap having identical sections, a padder would be required only for the 
oscillator circuit -- remember that trimmer hanging on the aluminum 
plate screwed to the right hand side of the command receiver tuning cap? 
That's the padder, used to calibrate the dial somewhere near the bottom 
of the tuning range.

Ted's use of a tap for the tuning cap eliminated the padder, meaning one 
less part for which ever circuit was tuned to the higher frequency -- 
the oscillator on the lower bands, the antenna and mixer on the higher 
ones.  This was a useful cost savings since these would have had to be 
rather precise silver micas or even a silver mica paralleled with a 
trimmer.  The cost came back in a bit of extra labor to make the tap but 
builders, presumably, had more time than money.

Use of taps on the coil or coils tuned to the lower frequency isn't as 
obvious.  Had he not done so he'd have had to fix the trimmer (across 
the tuning cap) to set the percentage tuning range and would have had 
only one possible inductance solution.  Use of a tapped coil allowed a 
smaller trimmer and a larger inductance, giving a higher Q (more gain, 
less bandwidth) again, without using another expensive part.

Walt Hutchens
KJ4KV

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