[NLRS] VHF Field Day modes

[Dr. Gerald N. Johnson]

On 6/17/2013 1:04 PM, Doug Reed wrote:
>
>
> Yup, Jerry is right about 45 baud. 45 baud was standard, 50 baud was
> oddball. Just another case of working from old memories and not
> looking it up....
>
> I agree with everything regarding narrow shift tones for HF/VHF SSB. I
> think we were using 850Hz wide shift tones in the 70's when there was
> RTTY on local FM frequencies but narrow shift is definitely a better
> choice for an audio FSK signal into a SSB radio. I had a Model 15RO
> running VHF autostart for many years. Its still in the basement along
> with a Model 38ASR.... I can't think of any reason I'd need either one
> again....

850 shift was standard for AFSK tones in the lat 50s into the 60s on 
VHF. To get 2975 and its sidebands out of the receiver and HF noise roll 
off had to be take out of the circuit or the audio taken at low level. 
Many an HF receiver had a .01 or .02 capacitor from the output tube 
plate to ground that made the output transformer into a low pass filter. 
It had to come when using speaker audio to the TU.

I sold my 15 without autostart when it still had ham value and started 
using a Data General Nova for some TTY generation. Its interface 
couldn't do 1.5 bit stop so I ran 2 bits stop and it sounded a little 
different on the air. I still have the TU that I built though it would 
need several new capacitors from not having voltage on the electrolytics 
for a few decades. And if your were to to try to run those machines they 
would need a long soak in penetrating oil and a thorough wash with an 
oil varnish solvent, like paint thinner to get the gum out of the 
bearings. The old instructions for oiling with none detergent 30 weight 
motor oil was faulty in that without modern additives that oil turned to 
gum in less than a year. Today something like Rotella 12W40 diesel oil 
would probably work for years, or better a synthetic motor oil.

I used a relxation oscillator designed for equal rise and fall slopes 
giving a symmetrical triangular wave and it came out of the SSB 
transmitter clean. That waveform has only 8% total harmonic distortion, 
and being and RC oscillator frequency changes were fast, requiring only 
changing the rise and fall slopes. It was far better for RTTY than an LC 
oscillator where the inherent tuned circuit Q or stored energy made for 
slow shifts with considerable transient.

I had a model 33 that I swapped for after it had caught fire. The motor 
failed while running and the flame was fanned across the base. I think I 
put $100 in springs, bushings, and felts to make it work and I installed 
a computer keyboard instead of the Matellish TTY keyboard. Tuning a 
model 33 was hellaciously difficult. The manual said set a spring 
tension or gap to some value with spring scale or feeler gauge, and then 
said, "refine the adjustment until the function works." Not at all like 
the more robust teletypes where setting to the specification was 
optimum. I traded the working 33 for a broken 38 printer and thought I 
had gotten the better part of the bargain but I never made the 38 work 
and I think I still have it. For several years I used a model 40 printer 
on my computers, it took a special case to be able to be in the same 
room with it, it was NOISY, a chain printer that was tolerably fast. 
Where a "bzzzt" of a dot matrix printer was a character, that same 
"bzzzt" of the model 40 was a line. I also used a BRPE paper tape punch 
and an optical paper tape reader on the Data General 1200 computer. The 
main shaft of the punch ran so fast paper tape flew a couple feet 
horizontally before it began to fall. Seems like it was 6000 RPM, for 
100 characters per second, or 10 inches per second tape speed. But it 
would happily produce fewer punches if needed.
>
> I found an article in a magazine about 10 years ago. Might have been
> RF Design or RF&  Microwave mags...It compared many flavors of simple
> omni vertical antennas, ranging through simple ground planes, vertical
> dipoles, bazookas with 1, 2, or more sleeves, J-poles, etc. My final
> take-away was that a simple quarter-wave ground plane with four
> radials angled down about 45 degrees not only was quick to build,
> simple to match, and has wide bandwidth, it also puts more of the
> radiation on the horizon. A J-pole has higher theoretical gain but is
> harder to build, far harder to match, requires a balun to reduce
> pattern distortion, and radiates at a higher angle above the horizon.
> I can also fold the wire ground plane into a small bundle for travel
> and just straighten out the wires when I get there....

You got it. The bazookas and j-poles do not decouple the feed line and 
modeled along they aren't bad but with a few wavelengths of feedline 
they radiate more like an end fed long wire nearly straight up with a 
null at the horizon. That's because of RF on the outside of the 
feedline. A ground plane modeled with feed line and only one or two 
radials shows the same effect, the third radial is a big benefit, and 
the improvement beyond 4 is hard to find.

Back in 1966 when I first moved to Ames, I used some corrugated 
downspout (given to me in eastern Iowa a few years before where I used 
it as a vertical and then in Texas as a support for an inverted V) to 
support such a ground plane about 30 feet in the air and in the days 
before repeaters had reliable contacts on 2m FM with mobiles in Des 
Moines about 25 miles distant. I KNOW its a good antenna, but its 
sometimes hard to convince those who only read QST.
>
> 73, Doug Reed, N0NAS.
>
73, Jerry, K0CQ