Pi as HF ham band transmitter and FM repeater

Question

If the pi is able to transmit fm signals from 1 to 250mhz wiht pifm and it has been used as an HF qrp transmitter why hasnt it been further developed as an HF transmitter with a small cheap amplifier? Also if it does transmit in the 2meter ham band why hasnt anyone built an FM repeater? Can the pi receive in the same frequencies it transmits?

Answer 1

As far as I know R_PI can only generate FM, by varying the frequency of an oscillator/timer.

This is no good for HF which uses much narrower bandwidths. You need to generate SSB which requires a lot of maths. Look up Software Defined Radios.

You could get software to generate what are called In-phase and Quadrature audio signals on the R_PI, several SDR programs do this. But you will then need some hardware to mix the IQ signal up to the HF frequency you want. Several HW designs are about on the wen for this.

A friend of mine has run Quisk SDR program on the R_PI as a receiver using a simple SDR from github.com/M6KWH.

Answer 2

If you properly filter the Pi's output before amplification and the antenna, and use a cheap RTL-SDR USB dongle for reception, you can use a Pi as a transceiver. See: http://www.rtl-sdr.com/building-a-ham-tranceiver-with-an-rtl-sdr-raspberry-pi-and-rpitx/ for one example project.