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Re: [Discuss-gnuradio] Works with GR 3.6, breaks with 3.7

From: Dan CaJacob
Subject: Re: [Discuss-gnuradio] Works with GR 3.6, breaks with 3.7
Date: Fri, 17 Oct 2014 05:08:23 -0400


I use the BE FLL for auto-doppler correction in the rare case where I am not actively correcting for doppler.  But, the correction is *really* slow.  I'm probably not using it correctly, but it works OK in that rare case when it's all I've got.

Very Respectfully,

Dan CaJacob

On Fri, Oct 17, 2014 at 2:28 AM, John Malsbury <address@hidden> wrote:

I researched this for a bit  (OK, maybe it was more like staring blankly)... unfortunately on a windows machine w/out git.  Nothing stands out at the momentt.  I'll give it another try tomorrow! =)

Also, I've never used the PLL blocks for freq demod before. Can you set something up with a graphical sink and send some snapshots showing what the output of that looks like? 

Also also, is the Band-Edge FLL ideal for GMSK?  My possibly, incorrect understanding of that block is that it was more ideal for PAM with common RRC.


On Thu, Oct 16, 2014 at 7:19 AM, Luke Berndt <address@hidden> wrote:
I just tried doing a complete PyBombs reinstall and that didn't seem the help. I checked and simple GRC files run fine. I can also see the signal where I expect it to be in GQRX, so I think my tuning parameters are correct. 

Are there some other things I should try? 

Sent from my iPhone

On Oct 13, 2014, at 1:38 PM, Luke Berndt <address@hidden> wrote:

I have a GnuRadio C++ program that decodes and records a SmartNet Trunked radio system. It is running great under GnuRadio, 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:

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,

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(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);


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