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Re: Doppler programming question

• Subject: Re: [amsat-bb] Doppler programming question
• From: "Don Woodward" <dbwoodw@xxxxxxxxxx>
• Date: Wed, 16 Jul 2003 08:13:34 -0400

```Without looking at the correctness of your code, I think you want to setup
Doppler gates on both frequencies and when the Doppler changes more than
say 50Hz then you change the frequencies, not just every 3 seconds.

73's

Don Woodward
KD4APP
AMSAT 33535
kd4app@amsat.org
http://kd4app.webhop.org

----- Original Message -----
From: "Phil" <phil@spiderweb.com.au>
To: <amsat-bb@AMSAT.Org>
Sent: Wednesday, July 16, 2003 00:15
Subject: [amsat-bb] Doppler programming question

Hello All,

I don't want to bore the group with a lot of programming code however it is
a
satellite related question and perhaps someone will be able to point me in
the right direction.

I'm trying to implement "the one true Doppler tracking rule". Downlink
tracking works perfectly (except for minor rounding errors), it's the
tracking that is giving me trouble.

Briefly, this is the logic behind my code:

1. get the satellite's downlink frequency (this is my rx freq)

subtract the Doppler shift for that freq from the receiver's frequency
save the result as baseRxFreq

This is the actual transmission frequency of the satellite.

2. get the satellite's uplink frequency  (this is my tx freq)

baseTxFreq = freqConstant - baseRxFreq;  // constant is 581800000 for FO-29

This is the actual reception frequency of the satellite (no problem here).

3. every 3 seconds do the following

get the Doppler shift for the baseRxFreq
rxFreq = baseRxFreq + Doppler;
setFreq(satRxVfo, (int)rxFreq); // set the receiver's vfo

Downlink tracking works perfectly.

get the Doppler shift for the baseTxFreq
txFreq = baseTxFreq - Doppler;
setFreq(satTxVfo, (int)txFreq); // set the transmitter's vfo

Uplink tracking doesn't work, it's the wrong tx frequency.

My uplink frequency logic seems to be wrong and with only two FO-29 passes
each day it's a little tedious to use the trial and error method to find
the
fault. So, I hope another set of eyes, or brain, will see the error in my
logic.

--
Regards,
Phil.

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