Re: [Discuss-gnuradio] Spurious Spikes in RX Data

[Sean Horton]

Hi Marcus,

I'm not getting overruns, and the signal source was the N210 (I was doing a loopback test). I switched to a hardware radio to transmit data, and the spikes went away. Is that what you'd expect? The spikes were 2000-3000 samples apart. If you don't think I should see those spikes even when the SDR is receiving from itself, I can investigate trying different frequency settings.

What equation can be used to calculate supported sample rates? Is it just clock (default 50 MHz, but I think it can be set to other values) divided by any integer value, only even integers, etc...? I just used the sample rate someone had chosen before I inherited the code, and it didn't generate any warnings about not being a value supported by the hardware (which is what I saw when switching the frequency to other values).

Thanks,

Sean

On Fri, Jul 14, 2017 at 1:52 PM, Marcus D. Leech <address@hidden> wrote:

On 07/06/2017 12:46 PM, Sean Horton wrote:

Hi,

I've recently gotten someone with Matlab to help me look at what's going on in my receiver. The image was created with matlab from data from a file sink connected directly to a usrp source. I am seeing spurious spikes when plotting I or Q, and I'm not sure where they could be coming from, or how to get rid of them. I know what I think I'm about to transmit doesn't have those spikes.

Some info that might be helpful:
Using a N210 with a UBX connected directly to my desktop.
I have tried a few sample rates (96000, 201613).
I am currently doing a loopback test, though working on getting the sdr to listen to a signal generated by another piece of equipment.
This doesn't stop me from being able to decode what is transmitted, but since my issue is I can't decode messages with as low of an SNR as I expect, I'm trying to examine everything as closely as possible. I'm off by 20-30 dB.
The entire path to get to matlab is: usrp_source -> file_sink -> Python's scipy in order to read in the raw data and store it in a .mat.

Also, if any responder would be kind enough to also point out how I properly respond, that'd be great. I know I can't just hit reply to the digest, and I also can't change the subject line when I hit reply in the digest, so I'm sort of stumped. I have had digest mode on, so I'll turn that off for now.

Thanks,
Sean

--
Sean Horton

Sean:

So, I'll note that for an N210, neither of those sample rates are supported precisely by the hardware.

Are you getting overruns when recording the data?

What is the source of the signal?

What frequency, and do the spikes come/go with frequency setting?





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Sean Horton