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 <[email protected]> > 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 > Kennesaw, GA 30144 > 1590 N. Roberts Rd., Ste 102 > Kennesaw, GA 30144 > Direct: 470-481-4054 > Fax: 678-594-5228 > > PROPRIETARY AND CONFIDENTIAL: This message, including any attachment, > is confidential information of Area-I, Inc. This message may contain > information that is privileged and exempt from disclosure under > applicable law and is intended only for the individual or entity to > which it is addressed. If the reader of this message is not the > intended recipient, or the employee or agent responsible for > delivering the message to the intended recipient, you are notified > that any use, dissemination, distribution or copying of this > communication is strictly prohibited. If you have received this > communication in error, please contact the sender immediately by e- > mail and destroy all copies of the original message and any > attachment. > INTERNATIONAL TRAFFIC IN ARMS REGULATIONS (ITAR) NOTICE: Any > drawings, specifications, or other proprietary data contained within, > or associated with this correspondence, or any subsequent > correspondence including, but not limited to U.S. Post, faxes, etc., > are considered controlled data. 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