<div dir="ltr"><br><div class="gmail_extra"><br><br><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>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div link="blue" vlink="purple" lang="DE"><div><p class="MsoNormal"><span style="font-size:11pt;font-family:"Calibri","sans-serif";color:rgb(31,73,125)" lang="EN-US">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>
<p class="MsoNormal"><span style="font-size:11pt;font-family:"Calibri","sans-serif";color:rgb(31,73,125)" lang="EN-US"><u></u> </span></p></div></div></blockquote><div><br></div><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><div> <br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div link="blue" vlink="purple" lang="DE"><div><p class="MsoNormal">
<span style="font-size:11pt;font-family:"Calibri","sans-serif";color:rgb(31,73,125)" lang="EN-US"><u></u></span></p><p class="MsoNormal"><span style="font-size:11pt;font-family:"Calibri","sans-serif";color:rgb(31,73,125)" lang="EN-US">Ralph. <u></u><u></u></span></p>
<p class="MsoNormal"><span style="font-size:11pt;font-family:"Calibri","sans-serif";color:rgb(31,73,125)" lang="EN-US"><u></u> <u></u></span></p><div style="border-width:medium medium medium 1.5pt;border-style:none none none solid;border-color:-moz-use-text-color -moz-use-text-color -moz-use-text-color blue;padding:0cm 0cm 0cm 4pt">
<div><div style="border-width:1pt medium medium;border-style:solid none none;border-color:rgb(181,196,223) -moz-use-text-color -moz-use-text-color;padding:3pt 0cm 0cm"><p class="MsoNormal"><b><span style="font-size:10pt;font-family:"Tahoma","sans-serif"" lang="EN-US">From:</span></b><span style="font-size:10pt;font-family:"Tahoma","sans-serif"" lang="EN-US"> <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><div>
<div class="h5"><p class="MsoNormal"><u></u> <u></u></p><div><p class="MsoNormal"><u></u> <u></u></p><div><p class="MsoNormal" style="margin-bottom:12pt"><u></u> <u></u></p><div><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>
<div><div><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><div><p class="MsoNormal"><u></u> <u></u></p></div>
<div><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><div><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><div><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><div><p class="MsoNormal">Nikos<u></u><u></u></p>
</div><div><p class="MsoNormal"><u></u> <u></u></p></div><blockquote style="border-width:medium medium medium 1pt;border-style:none none none solid;border-color:-moz-use-text-color -moz-use-text-color -moz-use-text-color rgb(204,204,204);padding:0cm 0cm 0cm 6pt;margin-left:4.8pt;margin-right:0cm">
<div><div><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><p class="MsoNormal"><u></u> <u></u></p></div>
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