[RTTY] extfsk & omni6

[Kok Chen]

On Feb 28, 2007, at 2/28    3:21 PM, Ed wrote:

> They actually shift the
> frequency via 2 crystals 170 hz apart.

The Omni 5 and 6 that I owned both had a single crystal for the LO,  
but they switched in a trimmer capacitor to move the frequency 170 Hz  
lower when Space is keyed.

> The reason I was trying extfsk was to determine why the Omni would no
> longer transmit in FSK. This all happened about the time I changed  
> from
> a desktop to a laptop computer. So was it the laptop or the rig.  
> Well I
> have determined its the rig itself. I plugged a 9 volt battery into  
> the
> FSK socket and the rig did not switch to transmit.

Did you reverse the battery polarity in your tests?  An input of 0 to  
-15 volts give the unshifted tone (mark) and an input that is between  
+2.5 to +15 will give you the shifted (space) tone.  A decent RS-232C  
signal should be able to key the FSK line.

In any case, it should be very easy to diagnose and fix yourself,  
Ed.  There are not that many components between the FSK keying signal  
and the actual crystal oscillator that can go wrong.

For the Omni 6, take a look at Fig 4-26 (page 4-45) of the Operator's  
Manual.

The FSK keying signal enters the Tx Audio Board from the lower left  
of the schematic.  See if transistor Q5 is switching when you key the  
FSK signal.  If it is, check the trimmer C18 (that is the one that  
applies the 170 Hz shift) and associated components.

If Q5 is not switching then trace back through Q9.   If the FSK  
signal is seen at the base of Q9 but Q9 is not switching, he is the  
culprit.

Check also the "RTTY T" line to make sure it is asserted when you  
place the rig in RTTY transmit mode.  This is the line that is tied  
to the emitter of Q9.

73
Chen, W7AY