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Re: [TenTec] Using Omni VI with MMTTY on FSK

To: tentec@contesting.com
Subject: Re: [TenTec] Using Omni VI with MMTTY on FSK
From: Jim <jlboockh@earthlink.net>
Reply-to: tentec@contesting.com
Date: Wed, 27 Aug 2003 23:16:30 -0500
List-post: <mailto:tentec@contesting.com>
Thanks for responses to my difficulty using my Omni VI+ and Omni V on
FSK with MMTTY. I received the following responese:

> FSK is strickly for RTTY or modes where only two tones are used. >It can only produce two tones - a mark and a space. For the PSK31 type >modes, AFSK must be used.

I agree. I have been using AFSK. The reason why I want FSK for RTTY is
so I can set the sound card for PSK31 and not have to change it for AFSK.

     > Why don't you post what line your are using from the PC and what
     > interface.

First I built an interface described by AA5AU at
http://www.aa5u.com/rttyinterface.html. It shows three different NPN
transistors on three different circuits that connect the radio FSK, PTT
and CW to three pins on the serial port DB9: pin 3 for FSK, pin 7 for
PTT, and pin 4 for CW. PTT and CW worked but not FSK. I also tried the
circuits provided with MMTTY that include two addional resistors and two
diodes with the same DB9 connections. Didn't work either.

Then I bought a Rascal interface from K4ABT at www.buxcommco.com, along
with his OmnI VI/V cable. The unit was advertised to work on FSK but the
cable he sells only provides the AFSK connections. His instructions are
unclear and he would not take the cable back. So I modified it to
provide a MARK/SPACE input to the Omni using a diagram he sent me. It
received FSK input from DB9 pin 3, just as in the AA5AU diagram. This
way, his Rascal is very similar to the homemade one I had tried earlier,
and did not work on FSK either.

>I use AFSK on my Omni VI but, after reading your question I decided to
>have a peek at my setup. Didn't take the time to play with FSK but
>did note that MMTTY's help file makes a distinction between FSK and
>AFSK in >setting up TX comm port parameters.

    >I'm sure this is too basic a solution, but did you review that section
    >of the Help file?

I made two changes on MMTTY. On the Option/Setup MMTTY/Misc tab I marked
the COM-TxD (FSK) option. (I later tried Sound + COM-TxD (FSK) but that
didn't work either.) I also set the PTT Port to COM 1. This must be correct. PTT seems to work since I get a pure tone rather than Mark/Space.

   >Works okay with my VI+.....you have to use the key (ptt) and the FSK
      >input. Check the voltages going into the FSK jack....Mark =<1Vdc
   >Space =>2Vdc. Sounds like you are only keying the PTT or the FSK
   >voltages are not right.

You may have identified the problem, but I don't know how to check the
voltages witout an oscilloscope, which I don't have. You cite the Mark
and Space voltages provided in the Omni manual. My understanding of the computer's serial port is that it provides either +5 volts or +12 volts, since these are what the motherboard gets from its power supply. Either should meet the Omni's Mark/Space requirements.

  >I used my Omni VI with true FSK and MMTTY no problems. It has been
  >awhile so do not remember details but if you have PTT and FSK lines
  >set up correctly and plugged in correctly it should work OK. Make
  >sure MMTTY is set up correctly for FSK.

It's good to know that someone has been successful at this. My problem
is finding out how to set it up "correctly" for FSK. To me, it's not

 >Are you using a USB / RS232 serial port converter on your computer?
 >Sometimes those interfaces will work fine for switching PTT but not
 >for sending data.


>Can you give some more details on the interfaces that you have tried?


>I've had no problem running FSK with my Omni VI - although I did
>notice that my tones seem to be more like 130 (rather than 170) Hz
>apart. I suspect that my rig needs some alignment.

If I have an alignment problem, it's with two different rigs.

>If you set the Omni to FSK then it expects an input to the Mark/Space >which is a DC toggle voltage. The sound card won't provide this and I >am not aware of any interface that converts the output of the sound >card to DC for true FSK mode. There are some interfaces, be they >hardware or software, that will take an RS-422 signal and convert to a >Mark/Space voltage but why bother. I used a PK-232MBX to generate true >FSK and it worked well. The default shift in FSK mode on the Omni is >180 Hz.. Using a sound card with two tones, high and low, the toggle >is typically 200 Hz. Never ran into any one that complained about the >error. Most folks don't even know about it and most decoders be they >true filter decoders or sound card AFSK decoders won't know the >difference either. Some say they can "hear" the difference. I say who >wants to listen to the crap. I just want it to print correct on the >screen on both ends.

>Yes the MTTY and AFSK is the correct way to do it via the sound card >and the audio in and audio out on the Omni.

Two responders above got the Omni to work on FSK using MMTTY. The FSK doesn't come from the sound card; it comes from the serial port. AFSK works for me too, so in that sense it is "correct". I think I will see if anyone on the RTTY reflector has any experience with this.

Thanks all es 73.

                                Jim  N4AL

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