[amsat-bb] Re: Listening on USB when operating CW

Patrick STODDARD (WD9EWK/VA7EWK) amsat-bb at wd9ewk.net
Fri Feb 7 09:24:58 PST 2014


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.
You're basically correct.

Stations using full computer control like what you get in SatPC32 will
be able to keep their frequencies steady at the satellite, but there
would still be some drift in what you observe on your SDR software's
waterfall display.  I also see this when I'm working those stations
with my portable two-radio setup, where I'm having to make minor
adjustments on both my uplink and downlink frequencies to keep up with
the other station.  For the mode B satellites where the operators are
only adjusting the higher of the two frequencies (uplink), it might be
easier to keep the downlink frequency at your receiver from drifting
so much.  There would be some drift at the satellite, but not so much
on your waterfall display.

> 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?

For the few times I have worked CW via satellite, I always set my
receiver to USB.  Without computer control, I would have to be
adjusting my receive VFO all the time to keep the CW signal in my
receiver's CW passband if it drifted.  My ear can do an OK job of
dealing with the drifting signal (changing pitch of the CW) when
the receiver is in USB.  When I use USB, I also avoid using any
narrow receive filtering.

For the FUNcube Dongle Pro+ and HDSDR, I only use USB on these
satellites.  I may widen the audio passband HDSDR has for USB,
but I don't bother putting it into CW when copying CW signals.



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