On 07/16/2017 08:38 PM, Sean Horton wrote:
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
Sample rates must be a proper integer fraction of the master clock rate,
which on the N210 is 100MHz.
The divisor (decimation ratio) should preferably be a multiple of 2, and
ideally, of 4.
Try at different frequencies. Try a very simple loopback
flow-graph--make sure you're using plenty of attenuation in the
loop-back cabling, or you'll
(A) risk receiver damage (B) get distorted samples.
On Fri, Jul 14, 2017 at 1:52 PM, Marcus D. Leech <[email protected]
<mailto:[email protected]>> 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
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