Comments inline... > OTOH, do it my way, there's ONE re-tuning step to start. Tune the radio. IF > shift remains constant - when the modem freq is constant, so is the > IF-shift. Passband width is the same either way. There's also ONE tuning > step to re-tune: Tune the radio. There's minimal AGC pumping because the IF > bandwidth is properly set the moment the signal is in the right place on > the waterfall.
I see what you are trying to do. But is this HF or FM at VHF or something? Basically you are suggesting the way we did it years ago on RTTY. We knew the frequency offsets were standard in the TU and thus the rig FSK readout was the mark frequency, and this was dialed in to get you on frequency. > Don't see the benefit of your way at all. Doesn't give you more space to > tune around in; makes external filtering hardware you might want to use > have to re-tune; adds tuning steps (or else commits you to use an open IF > bandwidth so that everything in the passband gets through, which isn't the > best idea I've heard recently, unless you like getting your AGC pumped by > that strong signal down-passband... entertainment value? challenge? :) Tuning like this is the only way that makes sense when tuning around for a QSO. That's not what I hear you wanting to do; enter one sked frequency and not tune around looking for a contact. Set the modem sweet spot where you want it and have the waterfall locked. Then the cursor can't be clicked to change the frequency. Dial the radio to the frequency you tell them and likely they'll be close. Still, there is going to be some minor tuning around based on radio calibration. > - just offhand - the rate of change of a lower frequency AF signal isn't > as fast as a higher one. That's why most AFSK signals are designed to > reside at the higher frequency side of the passband - e.g., SSTV isn't 300 > Hz sync and 500 Hz to 1300 Hz, it's 1200 Hz and 1500 Hz to 2300 Hz. If you > move stuff to the lower end, you're not doing the frequency response of > the channel any favors that I'm aware of. Rate of change has nothing to do with the choice of higher frequencies for the modes mentioned. Passband ripple and filter response rolloff are the reasons the higher frequencies were chosen. Additionally when set this way, any overdrive is likely to place harmonics of the AF frequencies out of the rig's filter passband on transmit. > That doesn't mean it's the right thing to do. It just means it was > something that could be done, and was. No one has yet to put a *benefit* > of this approach on the table. Well heck, I think it's easier that way. It is the way I intuitively operate and have for years. It works. Your way would be too confusing for me. > I've pointed out that it adds unnecessary > tuning, compromises optimum IF settings requiring resetting (or expose you > to AGC pumping), can lower the signaling rate, and compromises external > filters requiring resetting. That's what the QSY function is for. > the > operator doesn't need to "know" anything other than (a) is the signal > where it belongs in the waterfall and (b) what they want to send. I would disagree there expecting the operator to know where they are transmitting. Exactly. WHer eit is in the waterfall is only one part of the entire issue. > Generally speaking, the sensible place for the (high[est] tone) is 2295 Hz, > same as RTTY 170, 450, 800. Space and any intermediate frequencies are down > from there. If one needs to re-tune, it should be done with the radio, so > that IF shift doesn't need re-adjustment, and so that it is one operation. You can already do that now. Set the modem's sweet spot there. Lock it. Tune the radio either using the dial or via the Fldigi CAT control readout. Or shut off the frequency display in Fldigi altogether. Just lock the modem and tune the radio. I think that's what you wanted? > Such a setting lets you use external AF filtering and other hardware, if > available, and also sets a convention so that the radio may be tuned, just > one step, instead of radio, modem, if shift, external hardware - up to four > or more steps. Yes. Not causal operating method, but I get what you are wanting to do. > > One of the things I used to do was set up VSATs. The frequency we were > > assigned was the center of the transmitted signal, not the frequency > > of the LO injection. As far as I can discern, the only place where > > "dial frequency" is "transmit frequency" is amateur radio. Everyone > > else uses the center of the transmission. Amateur radio does not use the dial frequency is the transmit frequency. The operator still has to know exactly where his signal is going. > ..then what's the benefit of trying to say to them "well, you're currently > sending signals from 14.231200 to 14.232300 Mhz"? They're not going to be > tuning any hardware filters to those frequencies. The numbers they NEED are > 1200 Hz, and 1500...2300 Hz. And 14.230 MHz. These numbers give you (1) the > correct radio receive tuning, (2) constant setting for filters, (3) the > correct radio transmit tuning, (4) constant AF conditions so that IF shift > remains constant if a signal comes up on another frequency. > > > Here is another way to look at it. When I see a 500Hz blank spot in my > > spectrum display, I want to be able to tell my buddy to transmit in > > the middle of that blank spot, not have to calculate a bunch of > > offsets in my head. > > Say you're on 14.230 Mhz. You see the blank spot. The Waterfall reads out > from 0 Hz to 3 Khz (for example.) You're on USB. The blank spot begins at > 2000 Hz. So, you tell you buddy to "tune up 2 KHz." No calculations > involved. If you *want* to do so, you can say 14.232 KHz, but we're all > used to moving a few hundred or a few KHz... aren't we? I know I am. "Meet > you up (or down) x KHz" is an unbelievably common AR form of message, I > have trouble believing anyone would balk at saying such a thing. In this > case, it's "meet you up 2 Khz." No big deal. Makes sense to me, that's the current convention. Lots of people specify the transmitted frequency like that, i.e. dial xx.xxx and audio 2000. Anyway, I guess I have about talked this to death. I think everything fits already into how things operate. I feel comfortable with it and I think you can do what you want too, not that I think it's necessarily any more efficient or easier that way, but it works. Rick Kunath, k9ao _______________________________________________ fldigi-alpha mailing list [email protected] https://lists.berlios.de/mailman/listinfo/fldigi-alpha
