[TenTec] Using Omni VI with MMTTY on FSK

Fri Aug 29 01:02:37 EDT 2003

----- Original Message ----- 
From: "Jim" <jlboockh at earthlink.net>
To: <tentec at contesting.com>
Sent: Thursday, August 28, 2003 04:16
Subject: Re: [TenTec] Using Omni VI with MMTTY on FSK

> 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,

Serial port outputs are positive and negative voltage...the rane is
something lik 5 to 15 V on either side.

> 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
> obvious.
>
>   >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.
>
> no.
>
>   >Can you give some more details on the interfaces that you have tried?
>
> above
>
>  >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
> n4al at arrl.net
>
>
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