[GreenKeys] Dovetron and ST-6

[telegrapher at att.net]

As there are gobs of rtty sigs on 20 meters today due to Field Day 
activity, i figured i'd spend some time playing with the Dovetron.  I 
still am after making it drive the ST-6 for local loop operation at 
least in the receive direction.  One thing at a time.

I think that you could go about this in two ways.  One being via audio 
which is supplied via the BNC connectors on the back side marked 
Diversity mark and space.  The other is to take the RS232 output, run it 
into a keying circuit or opto isolator and drive the loop keyer circuit 
in the st-6.  I'm no engineer so if any of you have thoughts or 
suggestions along this line, i'm sure the Dovetron owners would love to 
hear about it.

As far as the audio portion goes, i took the receiver 600 ohm audio out 
and ran it into the Dovetron.  Guess what.  The Diversity output 
connectors provide audio but at a much lower level.  It seems to follow 
the signal strength of the received audio input.  In the case of my 
FT-990, i get about a -18 Dbm out no matter what the rec. vol. control 
is set at.  I could crank it up to -0, and might but for now it works 
fine with the ST-6.  As you only get either mark tone or space tone out 
of the diversity ports, it certainly provides a different audio tone 
input to the ST-6.  If you make that connection, say from the mark 
output on the Dovetron to the AF input on the ST-6, you'll see the meter 
react as if there is only one tone.  Of course the ST-6 likes both tones 
simultaneously so YOu won't see a good solid meter reading no mater how 
strong the signal is because the Plus Plus line in the ST-6 has no mark 
or space tone, whichever is missing, to reference or compare to.  Also 
you'll see that the meter peaks will fluctuate as to signal strength.

Now a though here is to either utilize a center tapped audio 
transformer, what impedance primary i don't have a clue, but i'll give a 
500-0-500 unit a try, hooking the mark and space output of the Dovetron 
Diversity jacks to each side of the transformer and then the output to 
the St-6 on the other side which can be either 4-8 ohms.  Mismatch 
indeed when the ST-6 wants to see 500-600 ohms for apparently best 
transfer of signal but it works.  I know this will drop the level to the 
ST-6 input down even further but it's try one thing at a time.  Probably 
the thing that will be needed is to have some sort of AF amp situation 
in the middle that would provide 20-40 db of gain which then would bring 
the input signal to the ST-6 up close to -0- max.  Such an amp with some 
agc or variable characteristics would be a plus.  I tried to measure the 
output of the Dovetron Diversity jacks with a meter down as far as -25 
and could see nothing so that output point can apparently be quite far 
down level wise.

As a side note, i had to turn off the limiter (go into AM mode) and also 
turn off the "Auto" switch to get the ST-6 to print.

I also noticed that the keyed tone output of the Dovetron Diversity 
points are dependent on the input frequency being quite close to 
whatever the tuning is set for.  In other words, even though you've got 
a good display on the crt, that doesn't mean the output audio is being 
keyed.  I'm using an FT-990 for a receiver.

The other thought is to take the MIL or RS-232 and run it into an opto 
coupler or some sort of keying arrangement to drive the loop keyer 
through pin F of board 3. I'd take that wire off of the card socket and 
run it to a switch on the back panel.  One side of the switch to the 
ST-6 circuitry, middle of the switch back to the ST-6 loop keying 
circuit and the other side of the switch to the loop keying board 
interface that comes from one of the two outputs of the Dovetron.  That 
would depend on which you want, EIA or RS-232.  BTW, i measure in idle 
state 7V on the MIL jack.

Anyway those are my thoughts about using the Dovetron into a more 
popular type TU used by amateurs.  As many of these units that have 
showed up, i'd think that more of us would want to put them to use. 
This commentary is just something that i'm throwing out for general 
consideration by the list and is not engineering other than my thoughts, 
simple as they may be.

If this is to far out, just hit your delete key.  I'll never know the 
difference.  At least i had fun on a hot Saturday afternoon in a 
relatively cool shack!

Larry
W0OGH