[GreenKeys] Dovetron Tempest further information

[Jack Hart]

The schematic for adapting the Dovetron "Tempest" terminal unit
to a HV loop is now on the www.rtty.com website thanks to George,
W7KSJ.

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For you PC computer users who don't need the HV
loop, I have some news...

I have completed some more clip-lead engineering and now
have the unit working with a standard RS-232 input from a
PC (I used Dave's TTYSIM and it works perfectly).

Here's all you need to do:

1) make up a cable that goes from your PC's COM1 port
to the Dovetron-

- if you have a 25-pin connector (DB25) for your COM port:
pin 2 to Dovetron "POLAR INPUT" connector
pin 3 to Dovetron "OUTPUT - RS232 -12/+12"
pin 7 to Dovetron GROUND (any convenient place)

- if you have a 9-pin connector (DB9) for your COM port:
pin 3 to Dovetron "POLAR INPUT" connector
pin 2 to Dovetron "OUTPUT - RS232 -12/+12"
pin 5 to Dovetron GROUND (any convenient place)

The cable is not critical...you can stick the wires into the
BNC connectors if that is your "style".

2) make sure the DIP switch on the inside regen
board, position #1, is set to EIA (not MIL).
It is clearly labeled on the board.

With TTYSIM you can jumper the AFSK output to the
AUDIO input and you will see what you type on the
PC screen. This checks out all of the wiring and
the TU's inner workings. You won't be able to see
what you're sending without some kind of
loop of the AFSK out to the AUDIO in. This could
be done with some relay contacts or by using the
"monitor" feature in your radio (my Kenwood
TS870 works that way).

The SEND/REC switch must be in REC and the AFSK
switch must be ON. If you are keying your SSB rig
with the AFSK tones, the AFSK switch can be used
with VOX as your Transmit/Receive switch.

The two Tempest units I have are set up for 850 HZ tones,
1575HZ Mark and 2425HZ space. I believe these tones
are compatible with the military gear (GRC106 and PRC47).
They're centered on 2000 HZ.

The tones can be internally changed with two pots
that are against the inside rear panel. You should be
able to get plenty of AFSK audio..it is set for 0 dBm/600 ohm
output. One of my units has a tone generator problem,
but the other puts out a tone level that I can hear across
the room when monitoring with my good old telco
"butt set". In fact, you might have to pad the tones
so you don't blow up your SSB rig. Don't depend on the mic gain
on your rig to control the tone levels.

If you have any questions about TTYSIM, contact Dave, N7EPI.
I used www.google.com to find TTYSIM (but then found I had it
on my old 386...which I used for the tests). The only
hangup is that you must use COM port #1, unless you
are adept at programming.

Just for information...I use a "standard" Dovetron to
run my TTY's and directly FSK the Kenwood with a series
switch circuit plugged into my HV loop.

Jack WA2HWJ

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