Doppler Correction

Posts: 9
Joined: Tue Jan 18, 2022 10:36 pm

Re: Doppler Correction


Unread post by radiohead »

I'm not familiar with uploading screenshots , but I'll give it a try.
RH2 shows VZLUSAT-1 about to pass my location in New Zealand.
LH2 shows the beacon being received, coming in from the right.
It is audible as it passes through the center frequency, then fades as it moves to the left.
If I want to stay on it, I have to use the mouse or direction keys.

Posts: 652
Joined: Thu Aug 13, 2020 9:47 am

Re: Doppler Correction


Unread post by Max »

So just to be clear, Simon has made it so that when doppler correction is active (which it seems to be from your screenshots) the sat signal should be fixed in the waterfall at the advertised frequency, namely in this case 437.240. That does not seem to be the case here. The received signal is somewhere around 437.242. That's odd because it's neither one thing nor the other. Doppler is shown as nearly 7 kHz (on the waterfall screenshot) so if doppler shift were not being applied at all, then the sat signal would be about 7 kHz off and drifting in (sorry brain won't work out which way or the other!) but anyway, not 2 kHz off as shown.

Imagine if at the same time as viewing the sat signal, there was another terrestrial signal somewhere nearby in the waterfall. With the doppler correction active, that signal would be drifting across the waterfall while the sat signal stayed static at 437.240. Hope not a stupid question, but are you 100% sure that the signal you heard drifting through is definitely identified as the sat signal and not some spurious ground based signal? That would then behave exactly as you have described. If doppler was not being applied then the sat signal would be drifting through as you have described, but the display clearly shows it's enabled so you need to test if it is or is not actually active

So as a "quick and dirty" test to check doppler shift is working, wait for any sat pass and doppler has become active (any passing sat will do, the sat it does not have to be audible), then tune to a known terrestrial signal, say a 70cms local repeater, zoom in as far as possible to still see the signal (exaggerates the "slant") and you should see (and hear) that signal drifting through it's frequency as the doppler is applied.


Posts: 9
Joined: Tue Jan 18, 2022 10:36 pm

Re: Doppler Correction


Unread post by radiohead »

Thanks for your time Max.
No, I can't be sure the signal I was hearing was from the satellite passing. But was near the same frequency & at the same time.
There are certainly a lot of them up there.
Being a newbie at this I have been compiling a list of active satellites with transponders.

Got around 70 entered into SDR Console.
So I am going by the frequencies from those sites.
I noticed after I had entered my list, a few of them showed with frequencies & modes.
For the majority, I had to enter them manually.

Regarding the simple test:
Still trying to focus my brain on that
I have certainly seen a slant on a signal in the waterfall.

I like the software, it's just getting to now how to best use it.

Posts: 1
Joined: Wed Apr 26, 2023 8:45 pm

Re: Doppler Correction


Unread post by ik6blo »

kudos to Simon Brown for his wonderful console sdr software .
I'm using sdrconsole with its satellite tracking to pilot Adalm Pluto both in reception and transmission.
I noticed that Doppler compensation only works in receive, not in transmit.
I think it would be useful to activate this function also in transmission.
73 de IK6BLO Roberto

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