I have a GnuRadio C++ program that decodes and records a SmartNet Trunked radio
system. It is running great under GnuRadio 3.6.5.1, but it doesn’t seem to be
working under 3.7.6.
3.6 is installed in /usr/local and 3.7.6 was installed in my home directory
using PyBombs. My updated program compiles against 3.7 with no problem and
runs. It will pick up a few of the trunking commands, so it is working, but the
ratios is about 1 to 100 compared to 3.6. I also tried running it in a Ubuntu
VM with 3.7 installed at /usr/local and had the same results.
I corrected for the change with XlatingFirFilter in 3.7, so it is the opposite
offset of 3.6. It looks like it could be a tuning error though, the flow graph
seems to be failing mostly at the CRC check. Did anything else change with
Blocks in 3.7? I looked at gr-osmosdr but I didn’t notice huge discrepancies
between the 3.6 and 3.7 branches.
Are there some obvious things I could be missing? I feel like this is something
small and stupid that I missing.
The diff between the two versions is here, smartness.cc is the main file that
decodes the control channel. As you can see, there is not that much different:
https://github.com/robotastic/smartnet-recorder/compare/master...3.7-Update#diff-73510702485a7dd2f7000285cbd5e557R40
<https://github.com/robotastic/smartnet-recorder/compare/master...3.7-Update#diff-73510702485a7dd2f7000285cbd5e557R40>
Here is the central code block that does it. Anything obviously dumb here?
float samples_per_second = samp_rate;
float syms_per_sec = 3600;
float gain_mu = 0.01;
float mu=0.5;
float omega_relative_limit = 0.3;
float offset = chan_freq - center_freq; // have to reverse it for 3.7
because it swapped in the switch.
float clockrec_oversample = 3;
int decim = int(samples_per_second / (syms_per_sec *
clockrec_oversample));
float sps = samples_per_second/decim/syms_per_sec;
const double pi = boost::math::constants::pi<double>();
cout << "Control channel offset: " << offset << endl;
cout << "Decim: " << decim << endl;
cout << "Samples per symbol: " << sps << endl;
std::vector<float> lpf_taps;
init_loggers(max_loggers, center_freq, samp_rate);
gr::msg_queue::sptr queue = gr::msg_queue::make();
lpf_taps = gr::filter::firdes::low_pass(1, samp_rate, 10000, 12000);
gr::filter::freq_xlating_fir_filter_ccf::sptr prefilter =
gr::filter::freq_xlating_fir_filter_ccf::make(decim,
lpf_taps,
offset,
samp_rate);
gr::digital::fll_band_edge_cc::sptr carriertrack =
gr::digital::fll_band_edge_cc::make(sps, 0.6, 64, 0.35);
gr::analog::pll_freqdet_cf::sptr pll_demod =
gr::analog::pll_freqdet_cf::make(2.0 / clockrec_oversample,
2*pi/clockrec_oversample, -2*pi/clockrec_oversample);
gr::digital::clock_recovery_mm_ff::sptr softbits =
gr::digital::clock_recovery_mm_ff::make(sps, 0.25 * gain_mu * gain_mu, mu,
gain_mu, omega_relative_limit);
gr::digital::binary_slicer_fb::sptr slicer =
gr::digital::binary_slicer_fb::make();
gr::digital::correlate_access_code_tag_bb::sptr start_correlator =
gr::digital::correlate_access_code_tag_bb::make("10101100",0,"smartnet_preamble");
smartnet_deinterleave_sptr deinterleave = smartnet_make_deinterleave();
smartnet_crc_sptr crc = smartnet_make_crc(queue);
tb->connect(src,0,prefilter,0);
tb->connect(prefilter,0,carriertrack,0);
tb->connect(carriertrack, 0, pll_demod, 0);
tb->connect(pll_demod, 0, softbits, 0);
tb->connect(softbits, 0, slicer, 0);
tb->connect(slicer, 0, start_correlator, 0);
tb->connect(start_correlator, 0, deinterleave, 0);
tb->connect(deinterleave, 0, crc, 0);
tb->start();_______________________________________________
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