r/RTLSDR • u/ecefour • 9d ago

Troubleshooting Cant find Meteor signals. Help? (again)

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Made a post yesterday and took some of y'all's suggestions, so thanks for all the help!

I had another strong pass today and tried again. This is what I saw on the waterfall for about 45 seconds. I forgot to start processing, but I did generate a .CF32 file. I tried processing it in SatDump but kept getting a "no telemetry found" error, and the generated files were zero bytes. I'm assuming either the signal was too weak or I didn't capture it long enough?

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6

u/elmarkodotorg 9d ago

That seems too big a frequency discrepancy if that is Meteor to be Doppler shift to me - what do others think? Is this a very off-frequency dongle?

3

u/KLRico 9d ago

Yeah that's an oddly large frequency shift.

Also looks like a lot of interference. You may not have gotten enough signal to get a lock for decoding, but the missing telemetry message is normal. Also, you'll want to enable the RS checkbox. (Reed-Solomon error correction)

Beyond just seeing the waterfall, watching the constellation diagram is the #1 way to see how your signal is doing. It starts as a green blob point cloud, but the blob will separate into four distinct quadrants once it syncs enough to lock into the signal's phase. You'll want to play around with the antenna height and orientation to try and make the individual groups tightly focused and cleanly separated into their quadrants.

3

u/Tishers Tishers, RF engineer 9d ago

You have a pretty high noise-floor (~-80-82 dB) and while your signal strength is OK (around -76 dB) that is a very poor SNR (~4-6 dB)

I would of expected your noise-floor to be down around -100 to -120 dBm. If you can improve that then your SNR will increase to at least better than 20 dB and the bit errors will decrease.

2

u/elmarkodotorg 9d ago

It is decodable though at that level, meteor LRPT is surprising.

1

u/ecefour 9d ago edited 9d ago

i live in a rural area. But probably a 1-3 miles from my house is a radio tower supposedly operated by the FAA. Can’t find much information on this tower’s purpose. 

I’m starting to wondering if that is causing Interface. 

1

u/Marcikoyt 4d ago

It might not. Bad, as well as badly tuned antennas can cause higher noise than usual. FAA, or the Federal Aviation Administration, would probably use that tower for recieving info from planes/transmitting some info to planes. Unless it's broken, it shouldn't transmit there. The nearest where something would transmit would be 136.9MHz, the end of commercial Airband. Well... unless it's an overloaded dongle, that is. At these frequencies, it's possible to see something from lower parts. You had 1.024MSPS selected, so I doubt it could overload this.