http://www.rtl-sdr.com/transmitting-fm-am-ssb-sstv-and-fsq-with-just-a-raspberry-pi/
Transmitting FM, AM, SSB, SSTV and FSQ with just a Raspberry Pi
Previously we posted about the Raspberry Pi’s ability to modulate one of its pins to produce FM transmissions with PiFM. A developer (F5OEO) has recently expanded on this idea, and now the Raspberry Pi is capable of modulating and transmitting FM, AM, SSB, SSTV and FSQ signals anywhere between 130 kHz to 750 MHz.
To transmit with the Raspberry Pi all you need to do is plug in a wire antenna to Pin 12 (GPIO 18) on the GPIO port and run the PiTx software by piping in an audio file or image for SSTV.
Important Disclaimer: While the output power is very small, you should still take great care as the carrier is a square wave, and there is no filtering on the antenna output. So any transmissions will cause harmonics all across the spectrum – possibly interfering with life critical devices. A filter *must* be used if you actually plan on transmitting with any sort of range further than your room. The predecessor PiFM has been reported to have a range of 10cm without an antenna, so it may be best to not connect an antenna to the pin if just testing. With a simple wire antenna the range is increased to 100m which could affect your neighbours. There are also strict laws and licences governing transmitting in most countries so make sure you follow them carefully. In short, get your ham licence and understand what you are doing before transmitting with any sort of amplification/range.
The code for PiTX can be downloaded at https://github.com/F5OEO/rpitx. Also see the authors (@F5OEOEvariste) Twitter account at https://twitter.com/F5OEOEvariste for some more info about PiTX.
Over on YouTube the author of PiTx has also uploaded a video showing a wireless doorbell being replayed with PiTx. On the video description he writes:
PiTx is a software which permit to transmit HF directly through a pin of Raspberry Pi GPIO. Unlike PiFM which transmit only in FM, PiTx is able to perform multi modulation (FM,AM,SSB,SSTV,FSQ) : it has an I/Q input to be agnostic.
The demonstration here is done in several steps :
- Record an I/Q file from a doorbell transmitter on 434MHZ (first part)
- Playing it with the Raspberry Pi using Pitx on HF on same frequency
- Listen to the doorbell receiver which recognize the signalConclusion : Pitx is now a real TRANSMIT SDR at very low cost. Be aware that it generate lot of harmonics and never compete with USRP or HackRF.
Goal is to popularize the transmission as rtlsdr popularize the reception.
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