Keith Regli wrote:
> I prefer using some isolation and adding an extra inverter stage.
I go along with Keith's suggestion. But the solution is far more
simple. All you have to do to key the OMNI 6 FSK is to build a
standard transistor keying circuit, using a resister to the EMITTER of
the FSK transistor, and GROUND the Base. So, for a DB9, just use pin 3
through a resister to the EMITTER, ground the Base, and connect the
Collector to the hot line of the FSK jack.
In effect this takes the RS232 level, which is correct, and inverts it
at the transistor. Now we have an "upside down signal". But since the
OMNI TTL levels are reversed, the OMNI reverses it again and you are
"right side up".
Big advantage is that you can also use the RTS line ( think it's pin 7
) to key the PTT of the OMNI using the standard transistor interface.
Don't forget to ground pin 5 to a common point. I use the Base ground,
shield ground,
rig ground, and pin 5 wire all at one common point. So, 2 resisters, 2
garden variety NPNs, 1 DB9 cable and you're in business.
Now, almost hidden in the OMNI 6 manual is a little line which says:
"When FSK is selected, you are using LSB for receiving." Solution is
simple; turn on the XIT of the OMNI and set it to + 1.41, and you will
be right on the money.
73
Ed
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