RPiTX Beta for Raspberry Pi 4 Released

Evariste (F5OEO) has just announced the release of an update to RPiTX which allows it to now be used on a Raspberry Pi 4. If you are unfamiliar with it, RPiTX is a program for Raspberry Pi single board computers that allows you to transmit almost any type of signal on frequencies between 5 KHz up to 1500 MHz with nothing more than a piece of wire connected to a GPIO pin. Evariste also notes that the new version is compatible with the beta 64-bit version of Raspbian.

Some examples of signals you can transmit with RPiTX include a simple carrier, chirp, a spectrum waterfall image, broadcast FM with RDS, SSB, SSTV, Pocsag, Freedv and Opera. You can also use an RTL-SDR to record a signal, and replay the IQ file with RPiTX. However, please remember that transmitting with RPiTX you must ensure that your transmission is legal, and appropriately filtered.

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  1. Lee A Carraher

    What’s the power output? My guess is that unless you have substantial amplification, you’d be weeky below anything that would violate fcc regulations.

      • Bertie

        I do not know, I would call 10mW (10dBm) being very optimistic.

        The GPIO pins on a RPi are 3.3v and into a 50 ohm load (impedance or antenna) that would in theory be a current of 66mA which would be a power of 217.8 mW ~23.4dBm.

        But all the GPIO pins on the RPi are limited to a maximum current draw of 16mA which means 52.8 mW ~17.23 dBm adding a filter to not vomit on the RF spectrum will reduce that by at least 3dB. But that would be a theoretical maximum, in reality that will reduced because there are impedance’s everywhere.

        So lets be very optimistic can call it 14 dBm output power. You might get that at the fundamental frequency of the square wave.
        But you are utilising the harmonics of a square wave, so the higher the harmonic frequency you use the lower the power. Most of the power would be in the fundamental harmonic frequency, then 1/3 the voltage at the 3rd harmonic (1/9 the power ; 9.54dB lower, so closer to 4dBm output power), 1/5 the voltage at the 5th harmonic (1/25 the power ; 13.98 dB lower, so closer to 0dBm output power), 1/7 the voltage at the 7th harmonic (1/49 the power; 16.90 dB lower, so closer to -3dBm output power), 1/9 the voltage at the 9th harmonic (1/81 the power; -19.08 dB lower, so closer to -5dBm output power), ….

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