Fm Radio in Pothos for windows

[Marcel van Langen]

Hello

I'm trying to make a fm radio in ptohos for windows but i cant find the wband fm receiver.
I try to make it with a guadrature demodulator but so far no succes.
My source is a dsr stick this is working and i can tune to a station on the fm band.
Now i want te demodulate the signal and get it on the speaker.
cane someone post here a sample how to this.

Greating Marcel

[Josh Blum]

Sorry about the lack of tutorials so far. But I think this would be a
very nice first tutorial for the SDR use case.

A very simple fm demodulator could be based off of this app for the
various parameters:
http://gnuradio.org/redmine/projects/gnuradio/repository/entry/gr-analog/python/analog/fm_demod.py

So I would use the sdr source, quad demod, FIR filter, and audio sink.
And give the FIR designer block similar filter parameters. I cant right
now, but I can give this a shot tomorrow and share the design.

-josh

[Marcel van Langen]

Thanks for the fast answer.

I have tryed what you told but i cant get it working.
I have some sound and i van here some music but that's it.
I wait for the design and then a give it a try again.

[Josh Blum]

Give this a shot. Its a save Pothos GUI design, just tested it on
windows and linux. Screenshots are on the wiki page:

https://github.com/pothosware/pothos-demos/wiki/Simple-FM-Demod

-josh

[Marcel van Langen]

Thanks, it is working great, now i have something to work further with.
I have already changed it to work with narrow fm.

Marcel

[Marcel van Langen]

Hello Josh,

I have tried to change the wide band receiver to a smalband one.
I thought it was working, but it is not very wel.
I wanted to receive with a band wide of 12,5khz.
So i think i need a Frequency Xlating FIR Filter.
But i cant get it to work.
Is it possible when yoy have more time that you can make a demo of a working smalband receiver.

Marcel

[Josh Blum]

On 05/26/2015 10:47 AM, Marcel van Langen wrote:
> Hello Josh,
>
> I have tried to change the wide band receiver to a smalband one.
> I thought it was working, but it is not very wel.
> I wanted to receive with a band wide of 12,5khz.
> So i think i need a Frequency Xlating FIR Filter.
> But i cant get it to work.

What specifically is the problem? You got to let me know if something
might be broken. There will be bugs, so I need to know to fix them :-)

Anyway, I did take a closer look at the translating filter, and it seems
to be working correctly. Since I put in the work to test it, I just took
a little extra effort to upload it to the demos page:

https://github.com/pothosware/pothos-demos/wiki/Filter-Design

> Is it possible when yoy have more time that you can make a demo of a
> working smalband receiver.
>

I have a lot of demos in mind, but I keep pretty busy :-)
If you happen to get something to work, don't hesitate to share it

thanks,
-josh

[Marcel van Langen]

Hello Josh,

It is not working by me, the remote environment crashed.
I have make a screen shot so you can see the problem.
I had the same problem by me when i tried to use the filter
but i thought i did something wrong.
I run Pothos on a windows 8 computer.
If you need more info i wil give you that.

Marcel

[Josh Blum]

Hey Marcel,

I didn't realize that some of the filter blocks were causing a crash for
you. Unfortunately, I'm not seeing it, but I may have an idea. So the
block labeled simply "FIR Filter" is behaving correctly for you in the
FM demodulation demo.

But the other filter blocks are from GNU Radio and use volk for SIMD
acceleration. It might be the case that something in volk, for detecting
SIMD architecture or loading the processing kenel crashes for your CPU
and not mine. Its just a guess, but it might explain why certain blocks
are causing a crash for your setup.

I'm curious: If you instantiate (lets say xlating fir filter) in a empty
topology, do you see the crash immediately? Also, if you run
volk_profile.exe (from the command line) does it complete successfully?

I will try to test this or more machines like windows 8, and CPUs with
AVX support to try and replicate the problem. In the meantime, you can
probably work around this by shifting the baseband samples with a
complex multiply with CW tone, and using the safe "FIR Filter" block
used in the FM demo.

I know things are buggy right now and I appreciate the feedback and
testing. -josh

[Josh Blum]

Hey all,

Just to give a quick update on this issue. It turns out that the
GNURadio FIR filter code had some bad pointer math in it. I will be
uploading new installers with the fix, look for the announcement soon.

This is the fix, more details in the commit:
https://github.com/pothosware/gnuradio/commit/20d9cbd9b27332ac39482152c4ba87834653ad20

Basically the pointer math was truncating the upper 32 bits. I suppose
that on my windows 7 testing, the virtual addressing always fit into 32
bits. But on windows 8, it seems that the addresses were consistently in
to the 64-bit range -- hence the crashing.

Thanks,
-josh