RTL offset with kalibrate-rtl

Nuno Gonçalves nunojpg at gmail.com
Mon Apr 15 09:48:36 UTC 2013


I have a stick with the R820T Tunner.

Using SDR# and SDR-Radio V2, and tunning to FRS and Airband
transmitters I determined that my offset is consistent to 54-63 PPM.

On the other hand kalibrate-rtl reports my offset to be about -30PPM,
also consistently accross several tests.

Is there possibly any difference from 100 (Airband), 400 (FRS) and
900ish (GSM) Mhz?

I am at Portugal, so the network is probably a GSM900 and also I don't
get something as NOAA narrow channels to figure this out.

GSM-900:
chan: 10 (937.0MHz + 27.986kHz) power: 29372.03
chan: 30 (941.0MHz + 26.850kHz) power: 197782.82
chan: 50 (945.0MHz + 26.645kHz) power: 86521.18
chan: 62 (947.4MHz + 27.109kHz) power: 29501.15
chan: 74 (949.8MHz + 26.605kHz) power: 56078.03
chan: 107 (956.4MHz + 26.442kHz) power: 57536.25
chan: 112 (957.4MHz + 25.319kHz) power: 31011.95
chan: 121 (959.2MHz + 25.145kHz) power: 87002.34

E-GSM-900:
chan: 10 (937.0MHz + 27.514kHz) power: 27631.40
chan: 30 (941.0MHz + 26.395kHz) power: 211497.68
chan: 50 (945.0MHz + 26.209kHz) power: 88871.46
chan: 62 (947.4MHz + 26.629kHz) power: 27770.99
chan: 74 (949.8MHz + 26.181kHz) power: 56274.60
chan: 107 (956.4MHz + 25.984kHz) power: 47437.43
chan: 112 (957.4MHz + 24.878kHz) power: 25791.29
chan: 121 (959.2MHz + 24.765kHz) power: 98473.19

What can be going on here?

Also, what is the reason for the dropped samples when sampling over
2.8MS/s? Is it a RTL2832 issue or something related to the USB driver?

Regards,
Nuno




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