[sdiy] FM Transmitter IC

[Tom Corbitt]

In terms of old chips, if you can find some from a decent source you can
always use the venerable BA1404; it was "the" goto pirate radio chip back
in the 90's

Here in the US they were used in the Ramsey FM10 which was the goto
armchair anarchist pirate radio station. They later updated to kits with
digital tuning like the FM-30 which ditched the 1404 for a PLL based
system.

I highly doubt you'll find any modern device that doesn't require an
additional cpu but if you're going to add a digital display and a tuner
button circuit  I feel like adding a simple mega or like cpu would make the
design of that part of the circuit so much much easier (not to mention you
really don't want to roll your own rf modulator anyway)

Si Labs makes some widely supported chips, the Si471X series, which you
could drive with a cheap micro and still have plenty of gpio to mux a 7
segment display and switches.

Better yet, unlike the old chips you also get RDS and a bunch of power info
so you could have your device look at the world and figure out the best
place for it to transmit before it started.(and the Si part also has two
GPIO lines you can use)

Great example design with code here:
https://learn.adafruit.com/adafruit-si4713-fm-radio-transmitter-with-rds-rdbs-support?view=all

I'm a huge fan of simple and reusable and doing things the "old" way (I
built and ran a pirate radio station using the ba1404 while at college in
the early 1990's) but the Tc and part/power variances made for quite a
juggling act. If I'd had access to the Si4713 back then I would have used
it in a heartbeat...

That would have allowed me to just waste all my time on better portable
antenna designs (the other rf black hole of time)

It seems small but even 250uV @ 3 meters was a decent amount of campus
coverage from the right height

Tom C


On Mon, Apr 25, 2016 at 10:18 AM, Neil Johnson <neil.johnson71 at gmail.com>
wrote:

> Apparently leagal as long as the power is very low:
>
> https://en.wikipedia.org/wiki/FM_transmitter_%28personal_device%29
>
> Looks like nanoWatts.  100uV is plenty for local reception -  a
> receiver should be happy with a couple of microVolts.
>
> Neil
> --
> http://www.njohnson.co.uk
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