[GreenKeys] ST6 questions

[Ralph Mowery]

----- Original Message ----- 
From: "Eugene Hertz" <ehertz at tcaf.org>
To: <greenkeys at mailman.qth.net>
Sent: Sunday, July 16, 2006 6:31 PM
Subject: [GreenKeys] ST6 questions


Hello all,

I've been using an ST6 from ebay for several years now.  It has always done 
good service but the motor control anti-space circuit never worked which was 
ok by me.  I never had a chance to really look into it in any detail.

Recently I acquired 3 more ST6s on ebay and now have been able to do some 
comparative anatomy between them all. Very interesting findings. One has 
obviously been built from a kit, 2 seem to be factory and the fourth is 
unknown.

So I took the best of the 3 new ones and began comparing to my regular ST6 
and I started looking at the frequency response. Here's what I got using my 
R&S Polarad SPN audio generator. ST6 #1 is one of the new ones, ST6#2 is my 
regular use TU.  Note that my regular unit does not have 425 shift.

ST6 #1 (new one)
MARK    SPACE   SHFT
2150 2330 180
2150 2580 430
2150 3010 860

ST6 #2 (regular use)
2160 2325 165
2140 2975 835

So, how important is it to have the frequencies right? Or is it more 
important to have the total shift right. In the case of the shift for ST6 
#1, they are pretty good varying 5-10 hz from expected. #2 is 5-15hz off a 
little worse.

Should I try to get the shifts more accurate to 5hz each?

My receivers only have BFO, no product detectors (YET) so I seem to always 
be able to tune the receiver or BFO to produce the right tones. However, I 
hope soon to own a product detector (outboard). How will this affect the 
need to have the tones accurate vs the shift?


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As Don said, unless you are transmitting, the tones do not matter that much. 
It is the total shift that does.  That should be within about 5 cycles. 
Wider spacing is the way to error.  That is you should be around 190 hz 
differance instead of 160 hz for the 180 hz shift.   If you are transmitting 
, all you have to do is match up the transmitted tones to the received 
tones.  That is if you leave st6#1 at 2150 and 2330 , you should set your 
transmitter tones for the same 2150 and 2330 hz if you are feeding audiio in 
to a ssb transmitter.  If you were using AM or FM on the VHF bands , then 
you would have to match the audio tones everyone else was using.

The above may be as clear as mud to you.  What I am getting at is that for 
receive only on the low bands , all you have to do is to have a tone 
differance of 180 hz.  YOu could use 2000 and 2180 just as good if that 
would make it past the filter that is at the front of the st6.  That is the 
one with 3 coils in it that you may or may not have.  You just adjust the 
reciever dial/bfo tuil the tones match what the st6 is set for.
I forget what they are but some were set up for what was a low tone pair 
around  1500 to 1800 hz for the mark tone.  That was because the ssb 
transmitters would cut off the higher tone frequency,, or atleast reduce it 
compaired to the lower tone, especially if the 425 or 850 shift was in use. 
To the station on the other end, he could not tell any differance in which 
set of tones were used as long as the shift was the same or very close to 
180 hz if that was the shift being used.

To adjust the filters you add or remove some turns from the coils.  Try to 
remove or add the same ammount to each side.  That is if you notice the 
coils seem to be wound from about half the form for one coil of wire and 
another coil of wire is wound on the other half.

You may want to get a few capacitors of the nominal value and swap them in 
tuil you find one that is a few hz lower and then remove a few turns of 
wire.  Or you could parallel the capacitors already in the st6 with some 
small value ones.

While I have not been looking at the comercial stations, if you set the st6 
for the 850 shift and tune for the maximum deflection of the meter it will 
copy any shift up to the maximum.  If there are no other stations close by 
in frequency it will work very well that way.  You do not tune the receiver 
for the mark frequency, but somewhat above it.  The st-6 follows the FM 
discriminator rules.  If  tuned so that the meter is tuned for max, the 
frequency comming out of the reciever will not be 2125 but somewhat above 
that for the smaller shifts if the mark filter is tuned for exectally 2125 
hz.