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How to Build a Raspberry Pi Radio Transmitter

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Re: How to Build a Raspberry Pi Radio Transmitter

#11

Post by unoti »

I'm a Ham radio operator, and interested in building my own real 2m/70cm transceiver that I can put in my car, complete with a little display to impress my friends and such. So these Pi articles interest me, but I'm more interested in interfacing a microcontroller to a real quality transmitter that can operate at, say, 25+ watts.

Ideally I'd like for this project to run Android, and drive my car stereo too, and do a bunch of other crazy things like GPS.

There's surprisingly little information out there on how to approach such a project. I've looked for components I could use on Sparkfun, and there's not really anything that jumps out at me, for either building 2m/70cm transceivers, or even for doing the stereo amplifier part.

I did find this fascinating article, though: http://hackaday.com/2013/02/28/hacking-a-ham-radio/

Re: How to Build a Raspberry Pi Radio Transmitter

#12

Post by synx508 »

startrak wrote: post #9

Anybody have information regarding the strength of the output signal? I know the FCC here in the US very touchy about radio broadcast strength...

It's definitely above the part 15 limits of 150 μV/m at 3m

I don't know the current drive capabilities of the Broadcom SoC, but let's assume it can perfectly drive a dipole antenna presenting around 72 ohms. The supply is 3.3V, I think. 3.3^2/72 = 0.15125W. In reality I doubt it's anywhere close to that, let's assume 50mW instead (it could be lower, I just don't know). According to a legit-looking field strength calculator I found online this works out to just over 0.5V/m at 3m! That sounds a bit high. Various factors would conspire to making even this much field strength unlikely, but it'd still exceed the FCC limits easily.

The Pi's output is also a reasonably decent square wave, as pointed out elsewhere. So there are some harmonics that are, themselves, above the part 15 limits.

In other words, don't do this, unless you have a spectrum analyzer, attenuator (don't forget to block DC). Actually, someone needs to do this with the right equipment just to find out how well it really performs.

Re: How to Build a Raspberry Pi Radio Transmitter

#15

Post by th0ma5 »

unoti wrote: post #11

I'm a Ham radio operator, and interested in building my own real 2m/70cm transceiver that I can put in my car, complete with a little display to impress my friends and such. So these Pi articles interest me, but I'm more interested in interfacing a microcontroller to a real quality transmitter that can operate at, say, 25+ watts. Ideally I'd like for this project to run Android, and drive my car stereo too, and do a…

Yeah I've been interested in the links out there around modifying the Baofeng radios and replacing the CPU in them with an Arduino or an generic computer interface.

Re: How to Build a Raspberry Pi Radio Transmitter

#17

Post by esbonsa »

cskau wrote: post #10

Does anybody happen to know if it's just as easy to read the pins at 91.25, 94.75, and 95.75 MHz? Lately I've been trying to find a way to do exactly that - initially using audio in - but so far without any luck.

it appears that you can use any frequency (if you use a proper antenna for the chosen freq., you will get better transmitting range)

Re: How to Build a Raspberry Pi Radio Transmitter

#18

Post by esbonsa »

edent wrote: post #2

This page basically says "Install this file, magic!" If you want the technical details behind it, a good starting place is http://www.icrobotics.co.uk/wiki/index.php/Turning_the_Raspb... Or the blog of the creator at http://www.omattos.com/node/19

I missed the icrobotics link that was submitted to HN 508 days ago unfortunately... but at least the link that I posted shows that you don't need any additional hardware to transmit on FM frequencies.
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