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Nikos Balkanas nikos.balkanas at eyeonix.comOn Fri, Jan 31, 2014 at 12:47 PM, Ralph A. Schmid, dk5ras <ralph at schmid.xxx>wrote: > GSM does not hop around inside its channel, this is wrong, the frequency > is +- some Hz accurate, at least in normal western European commercial GSM > networks. > > > Are you sure about that? Check it out: https://svn.berlin.ccc.de/projects/airprobe/wiki/A Legend of first picture. If still in doubt that *most" GSM carriers are hoppers, use rtl_power to scan your region ;-) Nikos > Ralph. > > > > *From:* osmocom-sdr-bounces at lists.osmocom.org [mailto: > osmocom-sdr-bounces at lists.osmocom.org] *On Behalf Of *Nikos Balkanas > *Sen**t:* Thursday, January 30, 2014 7:35 PM > *To:* Richard Koch > *Cc:* osmocom-sdr at lists.osmocom.org > *Subject:* Re: kalibrate-rtl results... > > > > > > > > On Thu, Jan 30, 2014 at 8:21 PM, Richard Koch <n1gp at hotmail.com> wrote: > > 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? > > > > Results seem OK. Do not forget that most BSTs hop around in their allotted > 20 Khz channel. > > So a result of +/- 20 Khz shouldn't surprise you. Best calibrate against > "anchor" BSTs that are steady. > > And yes, recommendation is to calibrate against 3 BSTs and correct for the > average or stddev if you wish... > > Nikos > > > > -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 > > > -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.osmocom.org/pipermail/osmocom-sdr/attachments/20140131/541216da/attachment.htm>