[SECC] RTTY and IC756PRO

[K4SB]

ku8e at bellsouth.net wrote:
>  I have found out since I bought my IC756PRO that it is a pretty good decoder/filters for recieving RTTY.  From what I understand you can transmit using AFSK thru the mic jack or FSK using some type of  TNC ???  Can I use the MMTTY program to do FSK or do I need some type of TNC/decoder ??

Yes MMTTY will do RTTY fine in either AFSK or FSK. However, if
possible, you should use
FSK because it is impossible to overdrive your rig on FSK, while you
run a good chance
of an excessively wide signal on AFSK.

Here's the setup.

1. Make sure your sound card is working OK.
2. Install MMTTY, it will automatically find the sound card.
3. Run an MONO connector from your Audio out or line out, ( if you
have only Stereo out, then use a stereo plug on the computer, and just
connect the 2 "hot" wires together at the rig end ) whatever to Audio
In on the rear of the 756. Most of us use a small isolation
transformer from RS in line with it. Transformer goes on the COMPUTER
end of the interface.

4. You will need a very simple interface from a comm port to your rear
PTT. Normally,
I use more than the 1K resister, usually at least 2200 ohms, and
better at 3300 ohms.
Any common NPN will work fine, but be sure to check the Base Emitter
rating. Wiring is from RTS on the comm port to the resister and then
to the BASE of the NPN. Collector goes to the PTT, and Emitter is
grounded. I usually use a 5 pin phenolic stand-off from RS and build
the interface on that. I also use a small prescription bottle and put
the whole thing in that. Be SURE if you do it that way, that you drill
holes in the cap and bottom of the bottle first!! Now, you need to add
another transistor to the pins for the FSK. It's identical to the
above, but the output cable of course goes to the FSK jack.  

UNLESS...A large number of rigs, for reasons I just don't understand,
are set so that
FSK is keyed "upside down". Simple solution. In para 4, switch the
Base and Emitter connections. Base to GROUND and the Emitter gets the
output from the resister.
In essence, the computer sends the FSK correctly, then the transistor
turns it upside
down, and then your rig turns it "upside down" again, which just
happens to be "right side up". You also need to read your manual and
see how the rig receives FSK. Most use
the LSB, which means you may need to use an offset. If you turn the
XIT on, and set it to +1.28 kc, that will do it pretty well.

AA5AUs RTTY page has many examples. It's simple, and a lot of fun. Be
sure to turn the
"scope" feature of MMTTY on, and set it to BEST.

73
Ed