Please do a packet capture of both problematic transponders separately. You should have the rtl-sdr command line tools installed. Run this:
rtl_sdr -f 5000000 -s 2500000 -g 20 -n 12500000 capture_rc4.iq
It captures 5 seconds worth of (12.5 million) samples around 5 MHz at 2.5 MSPS. You'll end up with a 25 MB file, compress it and send me for further analysis to
[email protected]; Please send the output of "openstint_rtlsdr" as well (from start to the first status message).
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I'm wondering what the problems can be...
While ghost detections are possible, they are extremely unlikely. There has to be a bit error which passes error-checking, and the same erroneous message has to appear twice to get reported as a passing. Possible, but unlikely. I think the decoder misinterprets a status message as a normal message somehow.
Transponder not detected at all: huhh... I've seen similar phenomena twice so far.
Firstly, too much gain overdrives the frontend, and symbols interleave with each other. In such conditions, preamble detection is not possible. The solution is easy (decrease the gain). There is a
tutorial on finding a proper gain with SdrAngel.
Secondly, it is possible that the transponder's clock is off by a good amount. The clock source on MyLaps transponders is extremely inaccurate, and they typically drift downwards in frequency as they age. If the frequency is off by ~19 kHz, detection is not possible (you'll see the exact phenomena as you describe).
There is
this line; try recompile with different values (ie. 5MHz-10kHz = 4990000), maybe it helps. @Oldfan suggested this fix long time ago anyway
