[Discuss-gnuradio] GR-Inspector Issues

[Shalom Dubinsky]

Hello,

My name is Shalom Dubinsky, and I'm having some trouble with the gr-inspector module.  I'm trying to use it to detect signals in the 2.4ghz range, and I can't get reliable responses from it.  Information on it seems scarce, so I'm asking here.

First, I tried playing with the default example of 3 cosine waves all summed with a noise source and run through the Signal Detector block.  This works as expected - both the GUI Inspector sink and the message debug output match. However, if I increase the sample rate too much it loses any accuracy it had.  Specifically, a sample rate of 4M only picks up two signals, and a sample rate of 40M only picks up one signal. The error is much higher in both of them, up to several hundred hz.  Decreasing it to 20k gives me two reasonably accurate signals and one garbage signal.

I also tried building my own graph.  I ran a single cosine wave broadcasting at 200M through a noise generator, the signal detector block, and the GUI Inspector block.  The sample rate was consistent throughout the graph, and the FFT length was set to 4096 across the board. The center frequency of the inspector sink was set at 200M.  The messages reported the signal to be at 8000000, while the graph displayed it as 208Mhz. Dropping the cosine frequency to 800k allowed the signal detector to work more or less correctly, but I had to change the center frequency of the inspector sink to 0 for it to display the signal correctly.  The problem at 800k was that the messages would alternate between ~800000 and ~-10183594. This isn't the only time I saw negative frequencies, either.

I next tried attaching it to a real radio.  When I broadcast a signal(from a different radio) at 2.425ghz, it detected that a signal was being broadcast, meaning it only reported something when I broadcast a signal,  but did not accurately detect the signal frequency. Instead, it would bounce around detecting different frequencies.

Questions:

* What is the relationship between sampling rate and signal detection accuracy?

* What is the relationship between fft length and sampling rate?  Is it related to signal detection accuracy?

* Why does it sometimes report signals with negative frequencies?

* Why does it sometimes seem to report a frequency delta?

* Is there anything else I'm missing about this module?

I've attached the gr-inspector example signal-detection .grc as well as the modified .grcs mentioned earlier.

Thank you,

Shalom Dubinsky

signal_detection_ghz.grc
Description: application/gnuradio-grc

signal_detection.grc
Description: application/gnuradio-grc

live_signal_detection.grc
Description: application/gnuradio-grc

signal_detection_usrp.grc
Description: application/gnuradio-grc