An Expansion Board with SMA Output for the Raspberry Pi and RPiTX

Thank you to Ihar Yatsevich for writing in and sharing his open source project called "rpitx-coax-pcb" which is an expansion board for the Raspberry Pi that converts the GPIO pin used by RPiTX into a coaxial SMA connector for easily connecting the output to an antenna. He notes that there are two revisions. One includes a filter in the in the GP1212 / GP731 case and the other does not. Filters in this type of enclosure can be found from Minicircuits. Finally he notes that he has not yet fully tested the design, but believes that there will be no problems.

The GitHub contains the EasyEDA design files, schematics and gerbers which you can use to print and build the PCB yourself.

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 wire connected to a GPIO pin. However, it is highly recommended that appropriate filtering be used if you are transmitting with an amplifier or longer range antenna as the RPiTX contains harmonics that can cause interference with other devices.

RPiTX Coaxial PCB Expansion Board for the Raspberry Pi
Subscribe
Notify of
guest

13 Comments
Inline Feedbacks
View all comments
Jerry Schull

Anybody done a 3D printed case compatible with this board?

N2

Jack, at the end of the day the “Operator” of said equipment is responsible for their actions.

Ihar Yatsevich

In the future, I may make a similar device (there are some problems with this at the moment, I recommend using a separate amplifier with good shielding for now), if there are any updates in the project, you will see them on the repository page.

N2

Would it be too much to ask for a Transmit/receive change over relay, and some 2.5mm/3.5mm jacks for a speaker mic?

Ihar Yatsevich

I did not plan to do this functionality. However, maybe in the future I will consider doing something similar, however with the additional use of GnuRadio and an additional SDR as a receiver.

Jack

Great…more INTENTIONAL, ILLEGAL radiators “because it’s fun and EASY to do!” Be sure to make it chic!

Syed

RpiTx is software designed for amateur radio operators and this is hardware designed to support RPiTx. If this hardware is used by a ham operating in ham bands, it’s not illegal. And if it’s used on a bench as test equipment, similar to a PlutoSDR or HackRF, it’s also not illegal.

Jack

“And if it’s used on a bench as test equipment, similar to a PlutoSDR or HackRF, it’s also not illegal.” Dood, polish your boot before you insert it into your wrecktum. #1 it “transmits” (horrible spurious trash) from 5khz to 1.5ghz ….that’s *NOT* an amateur radio device, if it was it would be locked to the amateur radio bands. #2 just because a “device” is being used on a “bench” does not make it a legal RF radiator….would be a great defense though for charging up a 10Kw amp and then saying…I was testing..it was on my bench…but..your honor….LOL

Billy
Bertie

And also read “FCC 15.103” section “(c)”, most SDR hardware are technically being sold as Test equipment, with a maximum output power of about 10 dBm (10mW or 0.71V across 50 ohms). If you deliberately wire that up to a 10kW amplifier, YOU are breaking the law, not the equipment manufacturer.

The RPi hardware on the other hand, a GPIO pin is current limited to a maximum of 16mA* so the maximum unamplified output power is theoretically on paper ~13mW (11 dBm, or 0.8V across 50 ohms), which is close enough to laboratory test equipment signal levels, if you hook it up to an antenna without filtering you are an idiot. If YOU deliberately wire it up to a 10kW amplifier, YOU are breaking the law.

*
The default for all GPIO pins is 2mA, which would be about
https://www.raspberrypi.org/documentation/hardware/raspberrypi/gpio/gpio_pads_control.md
https://github.com/F5OEO/librpitx/blob/master/src/gpio.cpp#L127

Billy

That armour case it nice, where the heatsink is the case or the case is the heatsink (search for “Raspberry pi Armor Case B” for the RPi4B in your search engine of choice).

N2

Very Neat! now can we have one with a Mini Circuits MMIC pill amp chip on it?

Ihar Yatsevich

In the future, I may make a similar device (there are some problems with this at the moment, I recommend using a separate amplifier with good shielding for now), if there are any updates in the project, you will see them on the repository page.