[RTTY] MMTTY difficulties

[ham at n0sq.us]

Kok Chen <chen at mac.com> wrote ..
> 
> On Feb 8, 2013, at 10:01 AM, ham at n0sq.us wrote:
> 
> > Already tried reversing the polarity.
> > 
> > Joe Subich, W4TV <lists at subich.com> wrote ..
> >> 
> >> Lee.
> >> 
> >> Check the RTTY Polarity menu in your TS-2000.  It probably needs to be
> >> set to REVERSE.  IIRC, the KAM takes care of that but your serial port
> >> interface would not.
> 
> Lets see if we can drill down a little bit.
> 
> If I am reading this correctly, you are 
> 
> 1) transmitting FSK through MMTTY, using EXTFSK,

No. I'm using MMTTY with N1MM logging software.

> 2) receiving through a second receiver with a KAM.

Yes.

> 3) and the KAM tuning meter shows that you have centered the two tones correctly.

Yes.

> 
> And, when you transmit, your transmitter keys properly, and you can hear diddles
> (instead of a single tone) coming from the receiver.  I also assume that the receiver
> and KAM can copy signals off the air?

Yes.

> 
> Correct so far?
> 
> If so, your transistor circuits are working.  And EXTFSK may be working (read on).
> 
> You said that you have tried reversing polarity, is that at the receiver (KAM end)
> or at the MMTTY end?

I reversed polarity in the TS2000 (MMTTY + N1MM software). The Kam+ is connected to a TS450.

> 
> If you are trying to reverse at the KAM end, do not do it by using the FSKinv command
> on the KAM.  That one controls the KAM transmit direction.  Instead, turn the KAM's
> INVerse state on and off.  (FSKinv and INVerse are different commands, one to control
> the transmit and one to control the decoding)
> 
> If that makes it work, and you can copy off the air signals on the KAM without
> inverting, you will need to invert MMTTY's output (see if MMTTY has an EXTFSK invert
> setting, or if the transmitter has an FSK invert setting). 
> 
> If you hear modulation through MMTTY's EXTFSK, and you still cannot copy by reversing
> the KAM, there is one more thing that is possible: you are throwing too many errors
> when using EXTFSK.  EXTFSK is really a hack, where the computer attempts to send
> the bits out every 22 millisecond.  If there is any timing latency in the OS, the
> output will not be close enough to the 22 millisecond bit periods that the KAM
> expects at the receiving end. Unfortunately, you need an oscilloscope to tell you
> exactly what is happening.  

I haven't tried EXTFSK yet. But, I do have access to an oscilloscope.

> 
> With most computers, the latency is around one tenth of a bit time (people will
> have more problems copying you when you are weak, but they will copy you fine when
> you are loud, so most people don't even know they have a problem, they just think
> the receiving end has a crummy demodulator).  But if you have an old, slow machine,
> it could be bad enough that few characters get through.  
> 
> If that is your case, some of your choices are: change software, use the K4DSP
> FSKit to convert AFSK to FSK, or just change to using AFSK transmit.

I want to try fldigi but it doesn't seem to have support for the TS2000.

> 
> BTW, you did not tell us what the KAM is printing while all of this is going on...
> is it printing nothing, is it printing complete gibberish, or is it printing a
> bunch of weird but repeating characters during diddles, or is it printing correct
> characters now and then?  Telling us that can help zeroing in on the problem.

It's printing gibberish due to noise and nothing when receiving a signal. I can hear the diddles in the TS450 speaker so I'm receiving at least that much. 

> 
> 73
> Chen, W7AY
> 
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