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Turning the Raspberry Pi Into an FM Transmitter

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bmarkus:
It works fine with piCore:

http://www.icrobotics.co.uk/wiki/index.php/Turning_the_Raspberry_Pi_Into_an_FM_Transmitter

Rich:
Hi bmarkus
That's pretty slick. But I imagine you'll also be transmitting on the odd harmonics of the carrier with that setup.

bmarkus:
Yes, for sure. If you really want it for real use (don't think so) you can add a simple filer or even better a power amplifier. What is erally great is the C source code which helps a lot to learn Pi hardware.

Anyhow, it's a great fun :)

Paulo:
Hi bmarkus

That is a nice trick using the IO pins to generate a carrier and some modulation.
Not having a Raspberry Pi, I'm wondering what the maximum "carrier" frequency would be?
There are of course other possible applications like a CW transmitter for the HF bands
or even a OOK data transmitter for the lower bands and even up to 400MHZ or so using an external upconverter
but this would involve extra hardware.

bmarkus:
According to upstream docs it works between 1-250MHz. As in Hungary we got the 70MHz HAM radio band in December 2012 I tried it in the 4m band. Origially it is generating Wide Band FM so I changed it to get NBFM 2-3 kHz deviation. A fellow HAM, HA5PT is located in next street in 500m dstance so my first QSO in the 4m band was made using this setup for transmit with pre-recoded voice messages. For reception I used an old portable broadcast receiver; we had so called OIRT band in the past in 64-73 MHz. It was working :)

He also confirmed, that unmodulated carrier is clean enough to use for CW mode, so it will be the next project. I'm planning a Python module to support CW operation. Also you can use it for HELLSCREIBER transmission as it is simple OOK, and another HAM friend, HA5FLT already developed a HELLSCREIBER TX/RX written in Python and Qt.

It is a fun.

You can listen how music is received in 500m distance using narrow band fm, sent on 70MHz, recorded by HA5PT:

http://www.xham.org/files/HA5DI_HA5PT_4m_S9plusz20dB.mp3

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