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@swbell.net wrote:
So VERY true! Thanks Bruce, ANDY w5acm
-----Original Message----- From: AMSAT-BB [mailto:amsat-bb-bounces@amsat.org] On Behalf Of Bruce Sent: Friday, April 13, 2018 9:40 PM To: amsat-bb@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
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