[amsat-bb] Mac Doppler

[Burns Fisher]

Oh, duh to me.  Thanks Paul.  I was not thinking straight.  Glad you all
solved it.

On Fri, Jul 10, 2020 at 8:34 PM Joe via AMSAT-BB <amsat-bb at amsat.org> wrote:

> aHHH tHAT MAKES TOTAL SENSE TO ME NOW!
>
> jOE wb9sbd
>
> opps cAPLOCK
>
> He is thinking on getting on the birds and asked me to help because I
> did do it many many years ago. he just bought a 9700. so is all excited.
>
> Any suggestions to send to him as to what birds to shhot for as well as
> antenna systems?
>
> Joe WB9SBD
>
> On 7/10/2020 6:59 PM, Paul Williamson wrote:
> > MacDoppler is correct.
> >
> > Doppler shift changes the effective frequency of a radio signal in
> > transit. When the satellite is coming toward you, the frequency of
> > both the uplink and downlink signal is increased by Doppler shift. The
> > goal of the computerized tuning is to maintain a constant frequency
> > *at the satellite*.
> >
> > So, consider first the uplink (your transmitter), and assume the
> > satellite is coming toward you. The computer needs to shift its
> > frequency DOWN, so that after Doppler has up-shifted the signal it
> > will arrive at the satellite on frequency. Now consider the downlink.
> > That is, the satellite’s transmitter (your receiver). That signal is
> > where it is, when it leaves the satellite. Then it gets shifted UP by
> > Doppler. In order to receive this signal, your receiver will need to
> > shift UP to match. Thus your two radios need to shift in opposite
> > directions to compensate for Doppler.
> >
> > Note that this is independent of whether the transponder is inverting
> > or not.
> >
> > For some discussion of why the goal has to be constant frequency at
> > the satellite, see my ancient article on The One True Rule for Doppler
> > Tuning, presently hosted at https://www.amsat.org/tag/tuning/
> >
> > 73 -Paul KB5MU
> >
> >> On Jul 10, 2020, at 4:27 PM, Joe via AMSAT-BB <amsat-bb at amsat.org>
> wrote:
> >>
> >> A buddy of mine just installed MacDoppler
> >>
> >> It seems to work great but he sent me a video that doesn't make sense
> >> to me.
> >>
> >> It is controlling his radio changing freqs as needed to account for
> >> Doppler.  BUT... I have never seen this before.
> >>
> >> the 144 band was changing one way in freq and the 440 band the other
> >> way.  Huh? That doesn't seem right in my head.
> >>
> >> anyone care to maybe explain whats happening?
> >>
> >> Joe WB9SBD
> >>
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>
> _______________________________________________
> Sent via AMSAT-BB at amsat.org. AMSAT-NA makes this open forum available
> to all interested persons worldwide without requiring membership. Opinions
> expressed
> are solely those of the author, and do not reflect the official views of
> AMSAT-NA.
> Not an AMSAT-NA member? Join now to support the amateur satellite program!
> Subscription settings: https://www.amsat.org/mailman/listinfo/amsat-bb
>