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Re: [RTTY] DESREVER

To: rtty@contesting.com
Subject: Re: [RTTY] DESREVER
From: Richard Ferch <ve3iay@rac.ca>
Date: Sat, 16 Oct 2004 09:20:33 -0400
List-post: <mailto:rtty@contesting.com>
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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