Re: [RTTY] DESREVER

[Richard Ferch <ve3iay@rac.ca>]

I agree with everything Bill, Chen and Goetz have just posted, and would 
like to add one more comment:

AFAIK, by far the easiest way to get your TX and RX out of whack with each 
other is to use FSK with a sound-card program like MMTTY. This is because 
in this situation the software sets the receive polarity ("right side up" 
vs. "upside down") but it's your transmitter that sets the transmit 
polarity. Since they are two different devices programmed by two different 
people, it's easy for them to be out of sync. In particular, I believe 
recent Kenwood and Yaesu radios assume the opposite polarity to the one 
assumed by JE3HHT in MMTTY, so on these radios you have to change one of 
the radio's menu items. On my TS-850, this is power on function no. 11, 
"FSK transmission key short: OFF(SPACE)/ON (MARK)". The default from the 
factory is OFF, but for MMTTY (and before that, for my old MFJ-1278 TU) you 
have to change this setting to ON. If I have understood correctly the 
postings I have read on this, FT-1000 series radios have a similar issue.

In AFSK, the transmit and receive polarities are set in the same place, so 
it is hard (indeed, with most software it may even be impossible) to get 
them out of whack with each other. It is, of course, easy to get them 
upside down compared to everyone else, but that's also easy to correct with 
one click of a mouse button.

Please note: I am NOT saying that AFSK is better than FSK. I am just saying 
that when you set up for FSK, you CANNOT assume that the polarities will be 
correct or in sync, you have to try it out and adjust until you get them 
coordinated. You don't have to worry about this in AFSK; in AFSK if you are 
receiving the right way you will automatically be transmitting the right 
way too. On the other hand, in AFSK you MUST NOT assume that your levels 
will come out right every time - you have to adjust your volume settings in 
the sound card and on the radio until you get a clean signal. In FSK, you 
can forget about level adjustments.

Getting the polarity right is, in the end, a one-time job which is usually 
easier to do than ensuring your signal is as clean as it can (or should) 
be. It's also harder to get it wrong subsequently by an accidental 
misadjustment (or simply by changing bands!). So from that point of view 
FSK is preferable because you only have to get it right once, not (in 
principle) every time you transmit.

73,
Rich VE3IAY


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