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Thomas Tsou ttsou at vt.eduOn Sat, Dec 31, 2011 at 5:16 PM, Avner Ezra <avner.ezra at yahoo.com> wrote: > 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? No, it most cases it means a weak signal. Kalibrate performs per-channel energy detection prior to offset calculation against the FCCH, which is always active. The variance is probably just noise. > 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). To capture 50MHz you need to 8-bit samples to avoid saturating the Ethernet bus. So yes it's possible, though I'm not sure about the current state of device or API support for the feature. > How can I wideband capture 125 ARFCNs? I tried to do it using: > ./uhd_rx_cfile.py -f `arfcncalc -a 512 -b 1800 -d` --samp-rate=25000000 -N > 200000000 -g 70 b1.cfile > > What I understood and decided to write such command above: > > B-1) arfcncalc calculates frequency of first GSM1800 channel (512 ARFCN) > which is start point (in above command) > 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 > B-3) 200M samples will be received (-N parameter) > B-4) Gain value is 70, means it will boost antennas to maximum power to > receive signals, I think USRPN210 max. gain is 80 > 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. You want the centre frequency of the spectrum you want to capture - not the start point. Also, the maximum gain value will also vary depending on the daughterboard. Otherwise, you are correct. > C) How can I seperate and process 200khz by 200khz channels in wideband > captured file? The brute force approach is to individually frequency translate each channel down to baseband, low-pass filter, and perform sample rate conversion. The more efficient method it to construct a multirate channelizer. GNU Radio has blocks for either approach, though construction may not be straightforward. Thomas