On Sat, May 1, 2010 at 12:55 PM, Anony Mous <[email protected]> wrote: >> > > 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.
That is convention. > 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. You got that right. I think we are arguing about different things here. Frequency convention came about in the days of AM and CW. In both those cases we report the carrier frequency, which just happens to be in the middle of the signal! In ham radio it became the convention to report the suppressed carrier frequency. BTW, if you look at how channels are defined in commercial SSB operation, they specify the passband width (3kHz) and a center frequency for the channel as that clearly defines precisely where the RF ends up in the spectrum. >> 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"? Because he needs to know precisely where his RF is going so that he doesn't operate outside the band. Here in the US the FCC doesn't give a rat's patootie what the dial frequency is, only if the RF goes outside the spectrum allocated to the class of license held by the operator. > I can easily understand why you'd want to know the AF frequencies involved, I don't, other than they represent an IF frequency, something important if I need to look under the hood but otherwise not so much. > 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. You are thinking too much from the point of view of doing things for the radio, not the radio doing things for you. > 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"? Uh, because the operator might not want a pink ticket? > 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), Why does it belong at 2125? I never use 2125 for RTTY. I happen to use 1500 because that is the center of my passband and I have my filters centered on that. I just switch the width to match the emission mode but they are still centered on 1500 Hz low IF. > 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. You mean by mentally setting your radio dial 2125 Hz below the frequency where you actually want to operate. I understand why you do that. We have been doing that in our heads for probably 75 years when operating RTTY. But that doesn't mean that it is what is really happening. It is what we do by convention to ensure that we put the signal where it should be in the RF spectrum. > 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. Uh, no. You and I could work all day long with me using a modem center frequency of 1500 Hz. Our dial frequencies will be different (who cares as it doesn't tell me where my transmit signal is anyway) but we will be able to work. The only difference is, I will know exactly the frequency of my RF output. You will have to expend some skull sweat to work it out. > 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. Well, confusion in the mind of the confused. The important thing is, "what frequency is my RF coming out on?" I would rather have the option of displaying that. -- 73 de Brian, WB6RQN/J79BPL _______________________________________________ fldigi-alpha mailing list [email protected] https://lists.berlios.de/mailman/listinfo/fldigi-alpha
