On Sat, May 1, 2010 at 1:29 PM, Rick Kunath <[email protected]> wrote:
> Comments inline... > > > 2. The frequency display on the radios is almost never the actual > > > frequency of the transmission. > > Correct No, it isn't correct. For an SSB mode, "the frequency" is where 0 Hz is. Other than that, the frequencies are all over the passband, and will vary hugely depending upon what you're doing. You're still tuned to the same place, though. > The radio dial frequency is the readout in Fldigi. The AFSK waterfall > frequency, added to that radio dial frequency, for the various audio tones, > is the frequency, or frequencies, of actual transmission. The operating ham > needs to know this. Ok. Here's the crux of the matter. Why does "the operating ham need to know this"? I can easily understand why you'd want to know the AF frequencies involved, so you can correctly tune the radio to the transmission and so that any filters, if shift, bandwidth adjustments can be made in a sensible fashion... the received information is pure AF once it's been detected... but I can't think of a single use for the information that "FAX black is received on 14.2319 MHz" when my receiver should be on 14.230 MHz USB, or "RTTY Mark is received on 14.07725 MHz" when my receiver should be on 14.080 MHz LSB. Please enlighten me here. What *is* fldigi's display of RF, as opposed to AF, frequency good for, and why does the operator "need to know"? On the other hand, if the waterfall is set to AF, and the modem is set correctly (let's say that RTTY mark is at 2125 Hz where it belongs), then I can tune the radio while looking at the waterfall during reception, and I'll be exactly on the correct RF frequency every time, by simply putting the mark signal on the mark frequency, 2125 Hz. Whereas... if the modem has been "slid" off the correct AFSK points, then I'll be receiving on the wrong frequency; my transmit signal will come back shifted to the original signal (which is what defines my frequency as wrong); my opposite number wil have to re-tune his receiver; and any external gear I might have - RTTY filters, SSTV receivers, etc., will be completely unable to deal with the received signal, because the AF frequencies are wrong. I think it is important to keep in mind that the vast majority of digital modes are sent and received as AFSK, not FSK, and that the cutesy trend to try and specify frequencies based on FSK mark for those few transmitters that actually have a mode that can be used for RTTY, for instance, is both confusing to everyone else, and not particularly useful in and of itself. In the end, these are AF frequencies for almost everyone. It behooves us well to treat them that way - almost everything works better that way. > ______________________________________________ > fldigi-alpha mailing list > [email protected] > https://lists.berlios.de/mailman/listinfo/fldigi-alpha >
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