FM Radio USB Dongles?

I’ve seen a lot of these $50 devices lately and I’m wondering if they
would be compatible with GnuRadio…

Anyone ever used one, and/or know how they operate? Hopefully they’re
just a front-end with a ADC that sends I/Q to the CPU for
processing…

Thanks,

Dave

On 11/10/06, Dave hartzell [email protected] wrote:

I’ve seen a lot of these $50 devices lately and I’m wondering if they
would be compatible with GnuRadio…

No support currently. Not likely.

Anyone ever used one, and/or know how they operate? Hopefully they’re
just a front-end with a ADC that sends I/Q to the CPU for
processing…

:slight_smile: 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.

http://www.silabs.com/tgwWebApp/public/web_content/products/Broadcast/Radio_Tuners/en/Si4700-01.htm
http://www.silabs.com/tgwWebApp/public/web_content/products/Microcontrollers/en/USBFMRadio.htm

The Toolkit is available from Mouser for $35 USD.
http://www.mouser.com/3plcart/cart.cfm?sid=63410000&pn=USBFMRADIO-RD

On Fri, 2006-11-10 at 14:19 -0500, michael taylor wrote:

:slight_smile: 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.

http://www.silabs.com/tgwWebApp/public/web_content/products/Broadcast/Radio_Tuners/en/Si4700-01.htm
http://www.silabs.com/tgwWebApp/public/web_content/products/Microcontrollers/en/USBFMRadio.htm

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
channels.)

10-bit audio doesn’t sound fantastic but there is probably room for some
DSP tricks to improve fidelity. They are oversampling by 3 since they
are only starting with 15 KHz audio in the transmitted FM signal.

AN264 refers to a reference design for Windows that implements the “over
the USB” protocol for data and control. It probably wouldn’t be all
that difficult to hack up a GNU Radio driver that did the same, not that
I’m volunteering. And each actual manufacturer may fiddle with the 8051
firmware to suit their tastes, so YMMV. On the other hand, these things
are commodity priced ($30-$50 retail), so I’d bet they are barely
repackaged reference designs with some cosmetic fluff wrapped around it,
and no changes to the firmware.


Johnathan C., AE6HO
Corgan Enterprises LLC
[email protected]

On 11/10/06, Johnathan C. [email protected] wrote:

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
channels.)

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.

On Fri, 2006-11-10 at 18:44 -0500, michael taylor wrote:

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).

Well, it’s been interesting enough for people to be selling $50 FM Radio
dongles by the bucketful :slight_smile:

The 96Ksps over USB is
irrelevant given the “IF” (output from the Si470x) signal is being
(lowpass) filtered at 23 KHz.

But since the original audio was only 15 KHz, you could lowpass filter
at the 96 Ksps rate and then decimate by three, increasing the effective
dynamic range above 10 bits. But see below…

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.

That’s the real limitation, to be sure. In fact, the USB controller
shows up as a Windows sound card, so you could use these with the
existing audio drivers and some fiddling for control. As the original
poster wondered, it would be far more useful to get downconverted I/Q
out of the thing. This would be great, for example, if someone ever
gets around to implementing an IBOC decoder for HD Radio.


Johnathan C., AE6HO
Corgan Enterprises LLC
[email protected]

On 11/10/06, Johnathan C. [email protected] wrote:

As the original
poster wondered, it would be far more useful to get downconverted I/Q
out of the thing. This would be great, for example, if someone ever
gets around to implementing an IBOC decoder for HD Radio.

That was along the lines of my thinking… HD Radio seems to be
getting tracking amount the broadcasters, especially in the SF Bay
Area. Yet the few available commercial receivers linger in the
$200-300 range.

An IBOC decoder, along with a cheap, 70-110 MHz USB receiver would
open doors for GnuRadio. Freely available decoding software might
allow manufacturers to enter the market with lower cost units.

In fact, I think the “market” for Digital Radio Mondiale receivers is
the freely available Dream software! I haven’t seen many
consumer-grade receivers.

Dave

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