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Re: [Discuss-gnuradio] FM Radio USB Dongles?

From: michael taylor
Subject: Re: [Discuss-gnuradio] FM Radio USB Dongles?
Date: Fri, 10 Nov 2006 18:44:19 -0500

On 11/10/06, Johnathan Corgan <address@hidden> wrote:
On Fri, 2006-11-10 at 14:19 -0500, michael taylor wrote:

> :-) Silicon Labs makes one chipset used in some. It has a 8051
> microcontroller and a FM Tuner chip. I think all those chips output
> Left/Right audio, not I/Q.
According to the reference design (AN264), they are taking the analog
out from the Si4700, putting it through a single pole 23 KHz lowpass
analog filter, then using the 10-bit ADC on the 8051 to go back to
digital.  The samples over the USB are at 96 Ksps, 4 bytes each (two

10-bit audio doesn't sound fantastic but there is probably room for some

The bigger limitation, in terms of flexibility, is "Worldwide FM band
support (76–108 MHz)" from their Features page of the Si470x single
chip FM receiver. I don't see the interest, it is a FM-only receiver
basically with the broadcast band (worldwide). The 96Ksps over USB is
irrelevant given the "IF" (output from the Si470x) signal is being
(lowpass) filtered at 23 KHz. You could add it to gnuradio, but it
would be for novelty's sake only, as you cannot make use of GNU
Radio's DSP features other than just with the audio output. GNU Radio
does not aim to be an audio DSP package, as far I know. There are
version of the chips available to do RDS (Eur) and RBDS (US) decoding
anyhow, so I don't even see any use there even.

That's my thoughts anyway.

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