[GreenKeys] Dovetron

[Ralph Mowery]

----- Original Message ----- 
From: "Larry Tighe" <larryradio at worldnet.att.net>
To: <greenKeys at mailman.qth.net>
Sent: Saturday, March 31, 2007 7:52 PM
Subject: [GreenKeys] Dovetron


> Hi Folks,
>
> Need some basic info (again) here.  I was trying a test with Gene and he 
> determined the shift was 850.
>
> Just opened the Dovetron and found the Mark and Space pots.  I put the 
> modem into the "MS" mode which sends Mark and Space from the local 
> oscillator right into the input circuit for testing.
>
> I set the Mark decode pot to 2125 and adjusted the osc. to Mark 2125.
>
> The BIG QUESTION is:  Should Space be 150 below or above the Mark tone?
>
> I seem to remember folks saying Mark is high.  Not sure.
>
> If this were on a wireline circuit...would Mark be low and Space high or 
> visa versa.  Is relationship different when used with LSB (radio) from a 
> wireline?
>
> Many thanks for the continuing patience.
>
>
> Larry
> K2JIA

Larry the high and low can be confusing.  If using audio tones the normal 
way is to set the mark to 2125 (or some other frequency) and the space to 
170 hz higher .

When using audio fed into a ssb transmitter you should then set the 
transmitter to lsb and due to the way ssb works your space will actually be 
170 hz lower if you look at the frequency on a counter.  When receiving the 
same signal, the tones come out inverted (is using the receiver set for lsb) 
and the space tone will seem to be higher in frequency.

Rtty  (two tone fsk ) was origionally sent by haveing a transmitter send out 
a carrier and then a capacitor was placed  across the coil or crystal and 
the space came out to a lower frequency.  Again the was at RF.  When ssb 
transmitters came into common use , it required the transmitter to be set to 
lsb to get the tones to come out at the correct RF relationship.

I hope I am not confusing you on how this works as it can be a difficult to 
follow or describe.