Linear Transponders: Listening on USB when operating CW

I posted the following on the AMSAT-BB:

I assume many home station satellite operators utilize some kind of
full-duplex radio or combination of two radios for CW on the current

Lately, as I have been listening a lot more with my FUNcube Dongle
Pro+, I have observed many CW stations drifting across the satellites’
passband.  I realize this is not a new phenomenon.  I would assume
these drifting stations are NOT using any type of computer Doppler
correction.  If they were using computer control, I would assume their
CW would stay on the same place in the transponder’s passband.  It is
visually apparent when the stations manually make larger frequency
movements because of the curve displayed on my SDR application’s
waterfall display.

Many times I have been engaged in a QSO only to have someone CQ’ing on
CW drift across my existing QSO.  Anyone who operates satellites has
probably had this happen to them many times.  Sometimes myself or
others in QSO may try to tell the CW operator “Hello – QSO in
progress” but it is apparent they are not hearing us.

My question is, does it make sense for people using CW on the
satellites to have their receiver set to USB?  Do some operators do
this?  If listening on a VFO with USB and had your transmit VFO set to
CW, would this help make it easier for CW ops to know when they have
drifted into an existing voice QSO?


There were several replies, but I felt W0JT replied very well:

I don’t think that the OP was trying to complain about SSB operators being less capable or less polite or less facile in their Doppler tuning correction or whatever in comparison to CW operators. He was just making an observation that sometimes two pairs of communicating operators have their frequencies “collide” due to shifting Doppler and different ways of tracking the tuning to compensate.

The issue is that (at least on all of my radios), when you are set to receive in CW mode the radio does narrow its bandwidth considerably to get the maximum benefit of CW’s narrower frequency bandwidth requirement, which is part of what makes it able to dig deeper into the noise level and pull out an intelligible signal. When I am set to receive in CW and tune in an SSB station (for example, during a terrestrial contest when there are lots of signals of both types present), I can’t understand the SSB conversation, but if I am set to receive in SSB, the radio sets a wider bandwidth and I can hear a CW signal quite well, and understanding it is mainly dependent on how well or poorly I can copy CW at all. So the OP was pointing out that if the CW operator was set to receive in SSB instead of CW, he would lose the selectivity of the narrower bandwidth but probably would still be able to copy the CW signal, with the added benefit of being able to hear and understand a SSB QSO whose frequency happened to collide with his CW operating frequency. No judgment was meant to be implied on who intruded on whom, or why (strictly because of shifting Doppler vs. different techniques of Doppler tuning correction). Just that for whatever combination of reasons, the two QSO’s happened to cross frequencies and intrude on one another. By listening in SSB mode the CW operator would become more aware of the intrusion and could better adjust his tuning to avoid it or move away from the colliding signal.

When I am operating in a terrestrial VHF/UHF/microwave contest, there are times when I can hear an operator well enough to copy him on SSB, but he is unable to hear me well enough to copy me on SSB. I will then switch to CW mode and send my information that way, counting on the superior legibility of CW (to an operator who understands CW) to get my information across. The problem that arises is that if the other operator copies my CW and realizes that I copied his SSB just fine, he may reply in SSB (because he doesn’t have to change any settings on his radio, he just hits the transmit button and talks), and with my radio set to CW mode, I can no longer copy him legibly. So I have to quickly switch back to SSB mode as soon as I finish sending my CW to hear his SSB reply. I guess my point is simply that while I have not experienced the exact problem that the OP was talking about, since I don’t normally operate CW on the satellites, I understand what he is talking about regarding the legibility of a CW signal in SSB receive mode vs. the illegibility of an SSB signal in CW receive mode.

Bottom line: if you can hear the CW coming down from the satellite well enough in SSB mode, it might very well be a good idea to listen in that fashion. It may or may not be easy to configure your radio(s) to transmit CW and listen to SSB, but if you can do it, and not lose the CW signal in the noise, it may be a good way to go.

73 de John Toscano, W0JT/5, AMSAT-NA LM#2292

My bottom line is that you can listen on USB and hear a little better than having your receiver VFO in CW mode.

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