[amsat-bb] Re: SatPC32 Help Needed

[Edward R. Cole]

David,
I'll step in here with a brief comment which you may already have considered:

Doppler frequency offset changes throughout a pass, so if you 
transmit on a fixed frequency on the uplink, the downlink frequency 
will change due both due to Doppler effects on the uplink and 
downlink frequencies.  If this is mode-UV the amount of Doppler will 
be more on the uplink due to the higher frequency.

Another effect that many do not take into mind is that Doppler 
changes at a non-linear rate; in other words it changes faster near 
the point where Doppler goes from positive shift to negative shift in 
the rest frequency of the satellite.  I know it sounds like a lot of 
math.  But as an operator you just need only realize that this will 
happen resulting in tuning the signal over the duration of the pass 
(tune faster at mid-point of pass).

When one gets up to modes like LS, it gets more challenging because 
both Doppler and rate of Doppler change are greater.  Probably should 
consider computer tuning of the radio at this point.

Note that Leo satellites go thru faster frequency change due to the 
quicker pass overhead.  Heo's taking hours for a pass require 
retuning less often.

Others may provide more definitive help with your question.
73, Ed - KL7UW

At 11:35 AM 10/6/2010, David Palmer wrote:
>Hi Guy and Amsat-List!
>
>I'd like to know the answer to this too!  I just recently started
>using twin FT-817ND's and SatPC32 as well, and notice the exact same
>thing -- audio drifts slightly thorughout the pass, even though I have
>the dopper correction set pretty close.  For me, it only drifts a few
>hundred Hz at most, but it's still enough that I have to tweak the
>offset on the uplink.  I'm new to SSB sats so not sure as well if
>there's something I'm doing wrong.  I've got the time on the PC clock
>set within 1 second, and my lat/long within 0.01 degrees.
>
>I'm measuring the drift just roughly based on my own audio coming back
>over the downlink -- unfortunately as I've called CQ on FO-29 and
>VO-52 the last few evening's passes (0100-0500 UTC), no one else has
>been on the sats for a direct QSO!  My own audio comes back nice and
>clear (even out to 5 degrees elevation) so it's not a reception
>problem, as far as I know.
>
>Any help for those of us new to the satellites would be appreciated!
>
>Thanks,
>
>Dave KB5WIA CM88 Northern California
>2xFT817-ND, Elk Log-Periodic, MH-72 Duplexer, Samsung Netbook running SatPC32.
>
> > Is anyone else using two Yaesu FT-817
> > / 857 / 897 rigs with SatPC32?  If so, what do you think I am doing wrong
> > and what are your DOPPLER.SQF data lines for AO-7, VO-52, and 
> FO-29 (as well
> > as any other critical settings)?
>
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73, Ed - KL7UW, WD2XSH/45
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