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G7CKF
Fri 10th Jul 2015, 09:35
I've been doing a lot of work recently with the Raspberry Pi as an RF source to improve Pi 2 support for a board I'm producing. Yesterday I completed a bit of proof-of-concept code that turns your Pi into a standalone QRP SSTV transmitter.

It takes the form of two pieces of software, a Python script that converts a JPEG into tone:duration pairs, and a piece of C that turns those pairs into RF. It's not necessarily the best code ever, but it shows what is possible.

Get it here: https://github.com/JennyList/LanguageSpy/tree/master/RaspberryPi/rf/sstv

Out of the box it's configured for the Pi 2, for a Pi 1 you'll have to uncomment the relevant line of code. There is a nasty timing correction constant you may need to adjust slightly too.

In action: https://www.youtube.com/watch?v=n3U1x13E_xU
The Pi RF output is taken to a 50ohm load and the HF receiver is loosely coupled with a bit of insulated wire wrapped round the load. For a real-world transmitter a low-pass filter is imperative. I am guessing 10mW should be enough to drive a simple linear amplifier circuit.

I challenge someone to have an SSTV QSO with 10mW! :) It should work up to 2m, but I've not yet tested that.