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List:       usrp-users
Subject:    Re: [USRP-users] USRP E313 | WBFM Issues
From:       Marcus_Müller_via_USRP-users <usrp-users () lists ! ettus ! com>
Date:       2018-09-24 18:10:41
Message-ID: 2591a47520d3dac2aa4b70ddfa587b2c469384e6.camel () ettus ! com
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Hi Ryan,

hm, there's honestly quite a few things that can simply go wrong on a
demodulation/DSP/signal side of things without nothing misbehaving or
you doing any mistakes. Your single-tone test hence was very clever to
do!

So, my recommendation is this:
First of all, verify that the reception strength / SNR is actually
reasonably good. You said you saw the signal in a frequency plot – so
how many dB were between signal and noise floor? If it's worse than
let's say 20 dB, you might need more RX gain or a better antenna (FM in
cities typically is pretty strong).

If that is fine, *make a raw recording* (using either GNU Radio with a
file sink directly attached through a head block to the USRP source, or
with the rx_samples_to_file tool) of a few seconds worth of samples,
and try to demodulate them on your PC – if that doesn't work, we know
there's something else to fix.

Best regards,
Marcus
  
On Fri, 2018-09-21 at 15:28 -0400, Ryan Campiz via USRP-users wrote:
> 
> Ryan Campiz <rcampiz@areai.aero> 
> Thu, Sep 20, 5:21 PM (21 hours ago)
> 
> to support 
> Greetings,
> 
> I'm having trouble with a basic Wide-Band FM (WBFM) demodulation
> tutorial. I am using the Ettus USRP E313. The Ettus USRP E313 is
> basically an enclosure with an Ettus E310 and Power/Ethernet PCB with
> the RF, DC Power, Ethernet, and USB ports.
> 
> FM DEMODULATION TUTORIAL
> In my application, as the host machine, I am using a Virtual Machine
> with Ubuntu 16.04 (64-bit). I downloaded all of the software as
> instructed in the AN-445 Ettus Application Note.
> 
> In my application, the tutorial that I am following is from the AN-
> 335 Application Note from Ettus. The tutorial is not complicated. I
> downloaded the Flowgraph files that the tutorial comes with. When I
> generate both python files and run them respectively on the E310 and
> the Host Machine, all I hear is static. I can see evidence of a
> received signal on the Frequency Spectrum graph, but I only hear
> static. What's more, as I vary the radio frequency, I do see the
> Frequency Spectrum graph change, but I see no evidence of any FM
> Radio Stations.
> 
> DETOUR: DEMONSTRATING I COULD AT LEAST HEAR A 1KHZ TONE FROM THE E310
> Just to make sure that it was possible to hear anything from the
> E310, I created a simple flowgraph for the E310. All it did was
> generate a Signal Source: a tone of 1kHz. On the other end, with the
> VM, I had an Audio Sink and a Time Graph and Waterfall Diagram. I was
> able to hear the tune. But it was choppy. And there was latency with
> the controls. A system block diagram of this set-up can be seen
> below. 
> 
> 
> LAST EFFORTS AND SPECULATION
> After demonstrating that I could hear at least a tone, I moved back
> to the FM Demodulation Tutorial. I tried for a day to get it to run.
> After no success, I used other resources to try to find where the
> process could be going wrong. Once such resource is the YouTube video
> "How To Build an FM Receiver with the USRP in Less Than 10 Minutes".
> That YouTube video is made by Ettus Research.  It was well-produced
> and easy to follow. However, even after watching it several times I
> could not locate what could be going wrong in the RF Demodulation
> flowgraph.
> 
> I am so uncertain at this point that I am starting to wonder if
> either:
> 
> A.      the RF Front End is not working, or
> B.      the OS image on the Ettus E310 is very slightly corrupted, or
> C.      the FPGA is not programmed (built?) correctly.
> 
> What could be going wrong?
> 
> 
> 
> 
> 
> Ryan Campiz
> Electrical/RF Engineer
> AREA-I
> where ideas take flight
> 
> 1590 N. Roberts Rd., Ste 102
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