Calibration / PPM

John john at tonebridge.com
Fri Aug 30 15:04:15 UTC 2013


I am trying to get my head around calibration of my RTL dongle.  I used 
gqrx with a known frequency (467.6375Mhz).  Based on this, the dongle 
needs offset of -16Khz.  In gqrx, this offset can be entered directly in 
the user interface.

With rtl_test -p, the PPM number varies.   I have gotten positive and 
negative numbers.

When using the RTL block in gnuradio companion, I need to enter PPM.  I 
have seen various formulas to calculate PPM from frequencies but for me 
they do not yield sane results.   I could be just misusing these formulas.

Any assistance would be appreciated.

Thanks,

John




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