kalibrate-rtl results...

Richard Koch n1gp at hotmail.com
Thu Jan 30 18:21:43 UTC 2014


I'm attempting to calibrate my RTL dongles. I notice they are
all about 2-4khz off if I compare against a known broadcast
station's frequency.

I am trying out kalibrate-rtl and am getting varied results.
I am in the US, so I did a 'kal -s EGSM  -g 20' and got the following:

        chan: 991 (928.4MHz + 26.986kHz)        power: 448020.99
        chan: 1002 (930.6MHz - 5.631kHz)        power: 320357.07
        chan: 1003 (930.8MHz + 16.192kHz)       power: 109489.92

Then 'kal -c CHANNELNUM -g 20'  for each channel number.

I then get the results below which the average frequency error looks
different for each channel. It is consistent though if I run them multiple times.

I would have expected less frequency error since I know that it is really only
about 4Khz off. Or am I not reading the results correctly?

-Rick

Using device 0: Generic RTL2832U OEM
Found Fitipower FC0013 tuner
Exact sample rate is: 270833.002142 Hz
Setting gain: 100.0 dB
kal: Calculating clock frequency offset.
Using E-GSM-900 channel 991 (928.4MHz)
average         [min, max]      (range, stddev)
+ 21.342kHz             [17837, 27433]  (9596, 3402.206299)
overruns: 0
not found: 199
average absolute error: -22.988 ppm

Using device 0: Generic RTL2832U OEM
Found Fitipower FC0013 tuner
Exact sample rate is: 270833.002142 Hz
Setting gain: 100.0 dB
kal: Calculating clock frequency offset.
Using E-GSM-900 channel 1002 (930.6MHz)
average         [min, max]      (range, stddev)
- 11.529kHz             [-15293, -5679] (9614, 3640.780273)
overruns: 0
not found: 194
average absolute error: 12.389 ppm

Using device 0: Generic RTL2832U OEM
Found Fitipower FC0013 tuner
Exact sample rate is: 270833.002142 Hz
Setting gain: 100.0 dB
kal: Calculating clock frequency offset.
Using E-GSM-900 channel 1003 (930.8MHz)
average         [min, max]      (range, stddev)
+ 14.283kHz             [9462, 19098]   (9636, 4777.044922)
overruns: 0
not found: 126
average absolute error: -15.345 ppm
 		 	   		  
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