I realise this radio is getting quite dated, but it's what I have. :)
One of the biggest obstacles to me for working the SSB birds is that the FT-726R doesn't have a proper RIT function. Instead the thing has a "Clarifier" which is active during both transmit and receive, and disables the tuning knob. So, I was wondering if anyone has ever modified the Clarifier to function as an RIT? It looks like it wouldn't be too hard; perhaps with an opto-coupler and a dropping resistor. I didn't find anything on the mods.dk site.
Bob - AE6RV
I don't understand why you'd need RIT...just tune the RX VFO? Is there a reason you need to keep track of the original RX freq?
At 15:28 2007-10-01, Bob Stewart wrote:
I realise this radio is getting quite dated, but it's what I have. :)
One of the biggest obstacles to me for working the SSB birds is that the FT-726R doesn't have a proper RIT function. Instead the thing has a "Clarifier" which is active during both transmit and receive, and disables the tuning knob. So, I was wondering if anyone has ever modified the Clarifier to function as an RIT? It looks like it wouldn't be too hard; perhaps with an opto-coupler and a dropping resistor. I didn't find anything on the mods.dk site.
Bob - AE6RV _______________________________________________ Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
Scott Townley NX7U Gilbert, AZ DM43di mailto:[email protected] http://members.cox.net/nx7u
--- Scott Townley [email protected] wrote:
I don't understand why you'd need RIT...just tune the RX VFO? Is there a reason you need to keep track of the original RX freq?
Without an RIT, you just wind up walking down frequency on each transmission, perhaps onto someone else. With an RIT, you're reset back to your original downlink frequency each time you transmit. With any luck, the other guy is doing something of the same sort, such as computer control, and you wind up sitting in the same spot for the entire QSO. To me, this seems like a good thing, since I do not have a computer controlled system.
Another thing is that this should cut down the flipping of the satellite knob back and forth from transmit to receive for each transmission. I'm looking at the Mouser catalog for solid-state relays. Maybe I can get something going.
Bob - AE6RV
I don't think that's true in the FT-726R. The RX and TX VFOs in satellite mode are not linked/tracking VFOs. As the other fellow drifts down, you can adjust your RX down to compensate. Your TX stays the same (from the ground). Since the VFOs are not linked, there is no difference between tuning the RX VFO down and tuning RIT down...the only advantage to be had is if for some reason you need to know your "starting point" RX freq. The only way to truly keep from walking is computer control. No dice with the FT-726R.
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).
At 18:54 2007-10-01, Bob Stewart wrote:
--- Scott Townley [email protected] wrote:
I don't understand why you'd need RIT...just tune the RX VFO? Is there a reason you need to keep track of the original RX freq?
Without an RIT, you just wind up walking down frequency on each transmission, perhaps onto someone else. With an RIT, you're reset back to your original downlink frequency each time you transmit. With any luck, the other guy is doing something of the same sort, such as computer control, and you wind up sitting in the same spot for the entire QSO. To me, this seems like a good thing, since I do not have a computer controlled system.
Another thing is that this should cut down the flipping of the satellite knob back and forth from transmit to receive for each transmission. I'm looking at the Mouser catalog for solid-state relays. Maybe I can get something going.
Bob - AE6RV _______________________________________________ Sent via [email protected]. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
Scott Townley NX7U Gilbert, AZ DM43di mailto:[email protected] http://members.cox.net/nx7u
--- Scott Townley [email protected] wrote:
I don't think that's true in the FT-726R. The RX and TX VFOs in satellite mode are not linked/tracking VFOs. As the other fellow drifts down, you can adjust your RX down to compensate. Your TX stays the same (from the ground). Since the VFOs are not linked, there is no difference between tuning the RX VFO down and tuning RIT down...the only advantage to be had is if for some reason you need to know your "starting point" RX freq.
Scott, If you can go back to your original downlink frequency, then it's only natural that when you transmit, you will set the transmitter so that you can hear yourself on that original frequency. This will keep You from drifting during the QSO. Having the ability to input an offset against only the other guys downlink, but not against your own, will allow you to effectively have two VFO knobs on the radio; one for his downlink and one for your own.
I actually got the idea for this from the Satellite Handbook, page 4-8, Table 4.3, Case 3, Note 1. But, my idea would work as an automatic RIT that turns itself off in receive.
Sure, I could solve a lot of these issues by buying a much newer radio, but I only paid $350 for this thing, and I enjoy messing with it as much as I do making contacts; perhaps more. :)
Bob - AE6RV
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
participants (3)
-
Bob Stewart -
John P. Toscano -
Scott Townley