[amsat-bb] Making the transponder sats as easy as the fm birds

Sat Apr 14 03:15:02 UTC 2018

Hang on, I'm a bit new to this, but that does not seem 100% right. We have
no control over the satellite frequency, so the ground station must
adjust... that seems obvious, but maybe I missed something or maybe you're
talking about satellites which are not on fixed frequency transponders ?

In any case, when the satellite is rising (or approaching), then the waves
coming from it will be compressed, so RX frequency at the ground station
will be higher than when it left the satellite. Since the satellite is
approaching the waves hitting it from the ground station will also be
compressed. So, both RX and TX will be higher in frequency.

The opposite happens when the satellite is descending (or moving away from
the ground station) i.e. waves from the ground station TX stretch in
chasing the satellite and waves coming into the ground station are
stretched as the satellite moves away, so both TX and RX will be lower
frequency.

Thus the ground station should tune up the band before the satellite
appears (AOS) and should reduce frequency (both RX and TX) as the satellite
rises, passes and sets. It will be above frequency at the start, on
frequency right overhead and lower frequency from just past overhead to LOS.

Or did I miss the plot ?

73,

Stephen
VE6SVJ
SKCC # 14855
Okotoks, AB

On 13 April 2018 at 20:49, Andy <w5acm at swbell.net> wrote:

> So VERY true!
> Thanks Bruce,
> ANDY w5acm
>
>
> -----Original Message-----
> From: AMSAT-BB [mailto:amsat-bb-bounces at amsat.org] On Behalf Of Bruce
> Sent: Friday, April 13, 2018 9:40 PM
> To: amsat-bb at amsat.org
> Subject: Re: [amsat-bb] Making the transponder sats as easy as the fm birds
>
> Sorry, this theory of thought is incorrect. You must adjust the higher of
> the two frequencies as it is most affected by Doppler. The true way to
> adjust is really to adjust both frequencies, however in the absence of
> computer control of both frequencies, you adjust the higher. Thus, if it is
> the receive frequency, then you adjust the receive, if it is the transmit,
> then you adjust the transmit. Holding the transmit frequency on the wrong
> band will cause you to walk across all the other QSO's taking place which
> is not a good practice.
>
> 73...bruce
>
> On 4/13/2018 8:41 PM, Eric Fort wrote:
> > I’ve had an idea for a long time as to making the satellites with linear
> transponders as easy to use as the FM “easy sats “.  Consider the following:
> >
> > As I understand it, the goal is to adjust your transmitter such that
> your frequency at the satellite is constant.
> >
> > Our tracking program gives us range to the satellite and its velocity
> relative to us given our location and the orbital parameters. From this we
> should have computed Doppler for both transmit and receive.
> >
> > We also know the frequency at the satellite of the various beacons
> > onboard. From this we can measure the doppler and work the other
> > direction
> >
> > If we transmit a subaudable tone of known frequency we should be able
> > to adjust the rx automatically by tracking the tone. (Acssb)
> >
> > Given these multiple ways of setting our tx/rx frequencies for our
> location can this not simply be automated to such a degree as to simply
> specify an offset from the beacon and operate as if it were a regular
> predictable opening on hf?
> >
> > Af6ep
> >
> > Sent using SMTP.
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>
> --
>
> Bruce Paige, KK5DO
>
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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: http://www.amsat.org/mailman/listinfo/amsat-bb
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