Scott Townley wrote:
Now someone is likely to correct me on that last statement...but even radios with tracking VFOs, track at a Hz-per-Hz rate, don't they? My IC-821 does...so if you manually tune, even with the VFOs in track, one link is a little off because they need to track at 3:1 (at least for VU and UV modes).
Yes, the VFO's track on a Hz-per-Hz basis, but this is not an error, it is by design. Remember, tracking of the VFO's has nothing to do with Doppler correction, where the amount of Doppler shift is proportional to frequency. The tracking of the VFO's has to do with positioning yourself within the passband of the uplink and downlink. On a linear transponder, once you are tuned in, moving 1 Hz on the uplink requires a 1 Hz move on the downlink (either in the same direction for non-inverting transponders, or in the opposite direction for inverting transponders) to stay tuned in. So if you hear your uplink coming down on the downlink in a quiet part of the passband, and tune the tracked VFO's to a new frequency where someone else is looking for a QSO, the downlink of your uplink should have followed you to the new frequency unless you took so long that the Doppler shift has changed significantly. But unless you tuned extremely slowly, you should be at least pretty close. Every so often, you have to adjust the frequency of the higher link without changing the frequency of the lower link to adjust for Doppler. On the FT-847, you either use the sub-tune knob to do that, or briefly un-lock tracking, re-tune, and re-lock tracking. And if the transponder is inverting and the ratio of frequencies is roughly 3:1 (mode VU or UV), the shifting Doppler is moving the two frequencies in opposite directions and so the net change in Doppler adjustment you need to make is closer to 2:1 than 3:1. Other modes have other ratios of changing Doppler, but at least for short periods of time when the net change in Doppler is small, a 1 Hz shift in tx causes a 1 Hz shift in rx, even mode V/S where the rx:tx ratio is over 16:1.
73 de WØJT