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<DIV style="FONT-SIZE: 11pt; FONT-FAMILY: Calibri,sans-serif">Though GSM spec has frequency hopping option, it can be switched on or off by operator. Yes, most operator switch it on.<BR><BR>I think You too are talking different thing. GSM doesn't hops inside each 200khz channel. It hops among multiple 200khz channel.<BR><BR>There is an exception: The downlink broadcasting carrier which carries FCCH SCH BCCH etc doesn't hop, and accordingly uplink RACH carrier doesn't hop either. These two uplink and downlink carrier frequency have a fixed 45MHz spacing if I recall correctly.<BR><BR>I think most of calibration programs use downlink broadcasting carrier to calibrate the dongle, because it doesn't hop and is easy to be captured.<BR><BR>You may also try my matlab calibration tool:<BR><BR>https://github.com/JiaoXianjun/multi-rtl-sdr-calibration<BR><BR><BR></DIV></DIV>
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<SPAN style="FONT-SIZE: 11pt; FONT-FAMILY: Calibri,sans-serif; FONT-WEIGHT: bold">From: </SPAN><SPAN style="FONT-SIZE: 11pt; FONT-FAMILY: Calibri,sans-serif"><A href="mailto:nikos.balkanas@eyeonix.com">Nikos Balkanas</A></SPAN><BR><SPAN style="FONT-SIZE: 11pt; FONT-FAMILY: Calibri,sans-serif; FONT-WEIGHT: bold">Sent: </SPAN><SPAN style="FONT-SIZE: 11pt; FONT-FAMILY: Calibri,sans-serif">2014/1/31 19:13</SPAN><BR><SPAN style="FONT-SIZE: 11pt; FONT-FAMILY: Calibri,sans-serif; FONT-WEIGHT: bold">To: </SPAN><SPAN style="FONT-SIZE: 11pt; FONT-FAMILY: Calibri,sans-serif"><A href="mailto:ralph@schmid.xxx">Ralph A. Schmid, dk5ras</A></SPAN><BR><SPAN style="FONT-SIZE: 11pt; FONT-FAMILY: Calibri,sans-serif; FONT-WEIGHT: bold">Cc: </SPAN><SPAN style="FONT-SIZE: 11pt; FONT-FAMILY: Calibri,sans-serif"><A href="mailto:osmocom-sdr@lists.osmocom.org">osmocom-sdr@lists.osmocom.org</A>; <A href="mailto:n1gp@hotmail.com">Richard Koch</A></SPAN><BR><SPAN style="FONT-SIZE: 11pt; FONT-FAMILY: Calibri,sans-serif; FONT-WEIGHT: bold">Subject: </SPAN><SPAN style="FONT-SIZE: 11pt; FONT-FAMILY: Calibri,sans-serif">Re: kalibrate-rtl results...</SPAN><BR><BR></DIV>
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<DIV class=gmail_quote>On Fri, Jan 31, 2014 at 12:47 PM, Ralph A. Schmid, dk5ras <SPAN dir=ltr><<A href="mailto:ralph@schmid.xxx" target=_blank>ralph@schmid.xxx</A>></SPAN> wrote:<BR>
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<P class=MsoNormal><SPAN lang=EN-US style="FONT-SIZE: 11pt; FONT-FAMILY: 'Calibri','sans-serif'; COLOR: rgb(31,73,125)">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.<U></U><U></U></SPAN></P>
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<DIV>Are you sure about that? Check it out:<BR><BR><A href="https://svn.berlin.ccc.de/projects/airprobe/wiki/A">https://svn.berlin.ccc.de/projects/airprobe/wiki/A</A><BR><BR></DIV>
<DIV>Legend of first picture. If still in doubt that *most" GSM carriers are hoppers, use rtl_power to scan your region ;-)<BR><BR></DIV>
<DIV>Nikos<BR></DIV>
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<P class=MsoNormal><SPAN lang=EN-US style="FONT-SIZE: 11pt; FONT-FAMILY: 'Calibri','sans-serif'; COLOR: rgb(31,73,125)">Ralph. <U></U><U></U></SPAN></P>
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<P class=MsoNormal><B><SPAN lang=EN-US style="FONT-SIZE: 10pt; FONT-FAMILY: 'Tahoma','sans-serif'">From:</SPAN></B><SPAN lang=EN-US style="FONT-SIZE: 10pt; FONT-FAMILY: 'Tahoma','sans-serif'"> <A href="mailto:osmocom-sdr-bounces@lists.osmocom.org" target=_blank>osmocom-sdr-bounces@lists.osmocom.org</A> [mailto:<A href="mailto:osmocom-sdr-bounces@lists.osmocom.org" target=_blank>osmocom-sdr-bounces@lists.osmocom.org</A>] <B>On Behalf Of </B>Nikos Balkanas<BR><B>Sen</B></SPAN><B><SPAN style="FONT-SIZE: 10pt; FONT-FAMILY: 'Tahoma','sans-serif'">t:</SPAN></B><SPAN style="FONT-SIZE: 10pt; FONT-FAMILY: 'Tahoma','sans-serif'"> Thursday, January 30, 2014 7:35 PM<BR><B>To:</B> Richard Koch<BR><B>Cc:</B> <A href="mailto:osmocom-sdr@lists.osmocom.org" target=_blank>osmocom-sdr@lists.osmocom.org</A><BR><B>Subject:</B> Re: kalibrate-rtl results...<U></U><U></U></SPAN></P></DIV></DIV>
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<P class=MsoNormal>On Thu, Jan 30, 2014 at 8:21 PM, Richard Koch <<A href="mailto:n1gp@hotmail.com" target=_blank>n1gp@hotmail.com</A>> wrote:<U></U><U></U></P>
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<P class=MsoNormal style="MARGIN-BOTTOM: 12pt">I'm attempting to calibrate my RTL dongles. I notice they are<BR>all about 2-4khz off if I compare against a known broadcast<BR>station's frequency.<BR><BR>I am trying out kalibrate-rtl and am getting varied results.<BR>I am in the US, so I did a 'kal -s EGSM -g 20' and got the following:<BR><BR> chan: 991 (928.4MHz + 26.986kHz) power: 448020.99<BR> chan: 1002 (930.6MHz - 5.631kHz) power: 320357.07<BR> chan: 1003 (930.8MHz + 16.192kHz) power: 109489.92<BR><BR>Then 'kal -c CHANNELNUM -g 20' for each channel number.<BR><BR>I then get the results below which the average frequency error looks<BR>different for each channel. It is consistent though if I run them multiple times.<BR><BR>I would have expected less frequency error since I know that it is really only<BR>about 4Khz off. Or am I not reading the results correctly?<U></U><U></U></P></DIV></DIV>
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<P class=MsoNormal>Results seem OK. Do not forget that most BSTs hop around in their allotted 20 Khz channel.<U></U><U></U></P></DIV>
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<P class=MsoNormal>So a result of +/- 20 Khz shouldn't surprise you. Best calibrate against "anchor" BSTs that are steady.<U></U><U></U></P></DIV>
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<P class=MsoNormal style="MARGIN-BOTTOM: 12pt">And yes, recommendation is to calibrate against 3 BSTs and correct for the average or stddev if you wish...<U></U><U></U></P></DIV>
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<P class=MsoNormal>Nikos<U></U><U></U></P></DIV>
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<P class=MsoNormal>-Rick<BR><BR>Using device 0: Generic RTL2832U OEM<BR>Found Fitipower FC0013 tuner<BR>Exact sample rate is: 270833.002142 Hz<BR>Setting gain: 100.0 dB<BR>kal: Calculating clock frequency offset.<BR>Using E-GSM-900 channel 991 (928.4MHz)<BR>average [min, max] (range, stddev)<BR>+ 21.342kHz [17837, 27433] (9596, 3402.206299)<BR>overruns: 0<BR>not found: 199<BR>average absolute error: -22.988 ppm<BR><BR>Using device 0: Generic RTL2832U OEM<BR>Found Fitipower FC0013 tuner<BR>Exact sample rate is: 270833.002142 Hz<BR>Setting gain: 100.0 dB<BR>kal: Calculating clock frequency offset.<BR>Using E-GSM-900 channel 1002 (930.6MHz)<BR>average [min, max] (range, stddev)<BR>- 11.529kHz [-15293, -5679] (9614, 3640.780273)<BR>overruns: 0<BR>not found: 194<BR>average absolute error: 12.389 ppm<BR><BR>Using device 0: Generic RTL2832U OEM<BR>Found Fitipower FC0013 tuner<BR>Exact sample rate is: 270833.002142 Hz<BR>Setting gain: 100.0 dB<BR>kal: Calculating clock frequency offset.<BR>Using E-GSM-900 channel 1003 (930.8MHz)<BR>average [min, max] (range, stddev)<BR>+ 14.283kHz [9462, 19098] (9636, 4777.044922)<BR>overruns: 0<BR>not found: 126<BR>average absolute error: -15.345 ppm<U></U><U></U></P></DIV></DIV></BLOCKQUOTE></DIV>
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