<html><body><div style="color:#000; background-color:#fff; font-family:times new roman, new york, times, serif;font-size:12pt"><div>Hi<br><br>I'm newbie in DSP and SDR, but I'm really interested in this matter and I want to learn. I have bunch of questions which has short answers, if you can please answer them in easy terms and words, so I can understand them well. I hope this thread will help a lot of other newbies to understand DSP stuff better.<br><br>I have a Linux with every needed tools like osmocomm, gnuradio, openbts, kalibrate, uhd drivers, ... and USRP N210 hardware ready. Everything works normal and well. <br><br>A) Sometimes when I scan a network bandwidth like GSM1800 using kalibrate, I see some channels like 820, 538, etc. When I re-scan, I cannot find them. Does this mean that kalibrate finds a channel when a mobile handset has a live conversation or sms send or receive in progress? or what?<br><br>B) I want to wideband capture for example
125 ARFCN. It needs 25MHz bandwidth which USRP N210 can handle and stream it easily. Even AFAIK I can double this number and capture 250 ARFCN using single N210 (50MHz, in USRPN210 data sheet it says it's capable of streaming 50MHz wide signals). <br><br>How can I wideband capture 125 ARFCNs? I tried to do it using:<br>./uhd_rx_cfile.py -f `arfcncalc -a 512 -b 1800 -d` --samp-rate=25000000 -N 200000000 -g 70 b1.cfile<br><br>What I understood and decided to write such command above:<br><br>B-1) arfcncalc calculates frequency of first GSM1800 channel (512 ARFCN) which is start point (in above command)<br>B-2) Sampling Rate is the bandwidth I want to capture, in our case it's 25MHz means 125 ARFCN which each ARFCN has 200kHz bandwidth<br>B-3) 200M samples will be received (-N parameter)<br>B-4) Gain value is 70, means it will boost antennas to maximum power to receive signals, I think USRPN210 max. gain is 80<br>B-5) My decimation rate here using 25M
sampling rate and USRP N210 which has 100MHz ADC, will be 4. So if I decided to read cfile I have to use 4 as decimation rate.<br><br>Please explain and tell me if I'm correct or wrong about above statements.<br><br>Does this will work and I'll have a 125 ARFCN from 512 to 637 ARFCNs captures into b1.cfile?<br>If so why in http://gnuradio.org/doc/doxygen-3.4/classusrp__source__base.html#adf8529d74696b7476e78bb0ef7b630af documentation, it says set_rx_freq should set center of frequency, so for example if you want to capture from 512 to 637, you should set frequency to frequency of ARFCN 574?<br><br><br>C) How can I seperate and process 200khz by 200khz channels in wideband captured file?<br><br><br>Thank you so much for your time<br>Your help and answers will solve problem of a lot of newbies like me.<br>Best Wishes</div></div></body></html>