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Re: [Discuss-gnuradio] GNU Radio Companion - ALSA

From: Cinaed Simson
Subject: Re: [Discuss-gnuradio] GNU Radio Companion - ALSA
Date: Sat, 18 Feb 2017 17:24:41 -0800
User-agent: Mozilla/5.0 (X11; Linux i686; rv:45.0) Gecko/20100101 Thunderbird/45.7.1

You have a plumbing problem.

On 02/18/2017 08:29 AM, Robin A. Jensen wrote:
> Hello all of you.
> I've just recieved my RTL-SDR dongle and is all new to this sdr-stuff,
> so please bear over with me, if i'm at the wrong place.
> I'm using GNU Radio Companion on a RPi 3 and no mather what i'll do, i
> can't get the sound to work.
> If a'im using rtl_fm and aplay, i'll get sound but it won't set on the
> radiostation. I'll take on that later.
> I've createt a small FM Reciever in GNU Radio companion and everytime
> i'll execute the script i'll get an error:
> RuntimeError.audio.alsa.sink
> I've been all over the internet to find a solution but with no luck.
> So now i'm have a hope that this mailling list can help me?
> My setup is:
> RTL-SDR Source: samplerate:  2M, frequency 96.5 MHz ->
> Rationel Sampler: Interpolation 4, Decimation: 1 ->

At this point, the sampling rate is 8 MHz.

If the interpolation was 1 and decimation 4 then the sampling rate would
be 500 kHz.

> Low Pass Filter: Sample rate: 2M, Cutoff freq: 100K, Transition Width:
> 100k ->

No indication of any decimation in the low pass filter - assuming a
decimation of 1 - or none.

> WBFM Recive: Quadrature: 500K, Audio Decimation: 1 ->
> Rationel Sampler: Interpolation: 500
> Decimation: 48 ->

Assuming a decimation of 1 in your low pass filter, the audio sampling
rate would now be 83 MHz.

Again, you need to reverse things - decimate at 500 kHz and interpolate
at 48 kHz.

I'd recommend deleting the first rational sample and decimating by 4 in
the low pass filter.

In short, interpolation up samples and decimation down samples.

> Audio Sink: Sample Rate: 48 KHz, Device Name: HW:0,0
> I've found that recipie on a Hack5 video and there it's working
> With best regards
> Robin.
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> Discuss-gnuradio mailing list
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