El 30/10/17 a las 23:23, Robert Bruninga escribió:

Im not following this closely, but the transponder I think is inverting. Thus the uplink dopper is subtracted from the downlink dopper whereas the beacon on the satellite is impacted by the full dopper of the speed of the spacecraft. So they will not be the same. Do the math and see if that comes out to the 1.26 you observed.

Hi Bob,

I'm not looking for a Doppler effect here. I've already corrected for that using the TLEs. It's the local oscillator drift in FO-29 that I'm trying to study.

However, I've done some math that matches my observed 1.26 within 5% error. The transponder is indeed inverting, with uplink on 145.95MHz and downlink on 435.85MHz. Assuming that the IF frequency f is below 145.95MHz (a 10.7MHz or 70MHz IF would be typical), there are two possibilities:

a) The first LO runs at 145.95 - f and the second LO runs at 435.85 + f b) The first LO runs at 145.95 + f and the second LO runs at 435.85 - f

In both cases, the total frequency shift through the linear transponder is 145.95 + 435.85. Assuming that both LOs are derived from the same oscillator (or that otherwise drift similarly), then the drift in the transponder would be proportional to 145.95 + 435.85, whereas the drift in the beacon would be proportional to 435.85. Now the quotient

(145.95 + 435.85)/435.85 = 1.33

matches the 1.26 I've measured within 5% error.

So for me this explains completely the effect I'm seeing, but it would be good to confirm it with the block diagram.

73,

Dani.

Hello Dany,

Try perhaps to check if your results match others tracking applications.

I do use http://amsat.org.ar/pass or http://amsat.org.ar/pass.exe with wispdde driver or HDSDR.

Using last 2 combinations, I follow LO-19 constant carrier receiving CW and software follows right on frequency, using either an FT-736 or FT-897.

To calculate Xmt & Rcv Dopplers, I take into account instant satellite velocity related to user ground station, always using the latest TLEs.

We can share formulas to calculate both Dopplers if that helps.

Best 73, LU7ABF, Pedro

On Mon, Oct 30, 2017 at 6:53 PM, Dani EA4GPZ [email protected] wrote:

Hi all,

A few days ago I have transmitted and recorded a (low-power) FT8 signal through the FO-29 linear transponder to test some Doppler correction algorithms I'm developing (see http://destevez.net/2017/10/wsjt-x-and-linear-satellites-part-ii/)

After Doppler correction, I'm left with a linear frequency drift both in my downlink signal and in the satellite CW beacon. However, the drift rate of my signal and the beacon are different. Specifically, my signal drifts 1.26 times faster than the beacon. I suspect that this drift is due to one of the local oscillators in FO-29.

To understand this better, I need to look at a block diagram of the FO-29 linear transponder. The best I've found is this:

http://www.jarl.org/English/5_Fuji/systeme.gif

However, I need something similar to this:

https://funcubetest2.files.wordpress.com/2010/11/funcube_ rf_board_block_diagramv2-1_pa3weg_open-1.pdf

Since I need to see the frequencies of all the local oscillators involved in the transponder and CW beacon.

Is there a more detailed block diagram for FO-29 or does anyone know something about this information?

73,

Dani EA4GPZ. _______________________________________________ Sent via [email protected]. 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