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Re: Doppler correct and frequencies - from a newbie!

Hi Alan,

"Alan K. Adamson" wrote:
> All,
> I'm kinda curious.  I've been tracking and copying the pacsats and I've
> noticed an oddity.  I'd just as soon not learn a bad habit, so I figured I'd
> ask.
> With automatic control and doppler correction, I can't seem to center the
> discriminator to keep the satellite decoding on the EVM.  How do others do
> it?  It goes like this.
> Take KO-23, the uplink is suppose to be 145.900 and the downlink is 435.175.
> So I setup the software with those values and when the sat comes over the
> horizon, I start to pick it up.  But the discriminator indication on the 847
> is way off to one side.  I've found that I have to crank in sometimes as
> much as 4K to get it centered and the modem decoding.
> So, my real question is as follows....
> Do you ....
> a) leave the uplink as calculated for doppler based upon the base freqs and
> center the discriminator (for best decode) on the downlink?  (in other
> words, just adjust the downlink)

Do the following.
> b) adjust both the uplink and the downlink to match the offset to center the
> discriminator
> I presume that both the TX and RX at the sat could vary different directions
> as time goes by, perhaps even away from one another.  You know where the TX
> is because you can center for that, but what is the preferred method for the
> RX.
> Do you also setup your software to counteract for this for each sat, so you
> don't have to do it manually?

> I don't want to learn any bad habits, so I figured I'd ask.  Thanks in
> advance,

No bad habits.  You will find this happens because of several reasons:

1.  Clock time is off in the PC.

2.  Keps are old or in slight error (the latter a real possibility).

3.  Your Lat/Long is not exact or close.

4.  Most likely, your radio is not exactly calibrated to be where the dial
says it is.  I checked mine here with two different commercial UHF test
sets (Cushman and Motorola) and found mine was off 3 kHz.  Even after
realigning it, there is still the need to adjust the WiSP downlink
frequencies a kHz or so.

73, Roy

Internet: w0sl@amsat.org
Home Page: http://home.swbell.net/rdwelch
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