Nexmon SDR: Using the WiFi Chip on a Raspberry Pi 3B+ as a TX Capable SDR

Back in March of this year we posted about Nexmon SDR which is code that you can use to turn a Broadcom BCM4339 802.11ac WiFi chip into a TX capable SDR that is capable of transmitting any arbitrary signal from IQ data within the 2.4 GHz and 5 GHz WiFi bands. In commercial devices the BCM4339 was most commonly found in the Nexus 5 smartphone.

Recently Nexmon have tweeted that their code now supports the BCM43455c0 which is the WiFi chip used in the recently released Raspberry Pi 3B+. They write that the previous Raspberry Pi 3B (non-plus) cannot be used with Nexmon as it only has 802.11n, but since the 3B+ has 802.11ac Nexmon is compatible. 

Combined with RPiTX which is a Raspberry Pi tool for transmitting arbitrary RF signals using a GPIO pin between 5 kHz to 1500 MHz, the Raspberry Pi 3B+ may end up becoming a versatile low cost TX SDR just on it's own.

15 comments

  1. AD5NL

    I did a bit more poking around on Google and I see that the Raspberry Pi 3b+ does not have the pads for a u.fl connector.

    However it does use a Proant PCB resonant cavity antenna similar to the RPi Zero Wireless. And there have been folks who have attached coax or antenna connectors to that model. (Looking at photos there are some differences but it looks like there is basically a trace that would be RF hot).I think it should be possible to cut the trace to the PCB antenna and attach coax there. Which can then be filtered, amplified and otherwise mucked about with RF components.

    Of course this would violate the warranty and the Raspberry Pi Foundation would disavow all knowledge (cue Mission:Impossible theme).

      • Peter

        i did some measurements and the pad is disconnected, yet there is a small space on the “lead” to the antenna which is unprotected, now the question is does it need a resistor or capacitor or can it be connected dierectly to the pad. They do use the pad for testing so it must get connected by the testing apparatus. Maybe if people demand pads for ufl the pi 4 will get it, if people dont demand then they wont do it.

        • Freedom Bastard

          the resister near the gap can be heated and slid from one path to the hidden antenna pad for a antenna jack. It is an actual pad for an antenna jack just lightly painted over. these are present on the pi zeo W and pi3b 3b+ 3A+ 4b. quite a few ppl have added the jack. its not FCC compliant to do this and thus some legality issues may arrise to selling a board after adding that port. I would recommend using a soldering micro tipped hot air gun as a regular solder iron may just suck up that tiny resistor. Graphite is a great tool for working with certian hot mediums, so a well sharpened pencil may suffice as the tool to push/slide the onboard resister by the gap in the path of the onboard into its new position. I would apply flux and tiny solder smiggin on the new receiving end first. You may want to add the jack before sliding the resister.
          studying the board it should be apparent where the painted over pads for the jack is as it is standard type seen on all PCBs.
          I will say there is also a jerry rigged method as well, if you have 1mm coax antenna at your disposal. many of the cheap andriod TV boxes do this. they simply strip the outer down a mm or 2mm and solder that direct to one of the ground pads, then the center line to the hot out end of that resistor (or if you slid the resistor to the pad for the + of the pack) it won’t be as good but these do work. I have a pile of s812 amlogic cpu’d SBCs from Gbox 2 TV boxes. all of them are cheaply done like this with just an antenna and no jack. The reception distance on these devices works well for wifi in a home, I am sure a more appropriate method would be better though.

    • Peter

      has someone tried putting an ufl conenctor on the 3b+? I do not want to break mine yet i want to connect a better antenna for wifi.

  2. Languagemaniac_

    I always wanted a raspberry pi but I never bought one but now I’m more into the sdr world and I wanted it more and more and I just read this and I thought “why not?”, I just bought it c’: It’s going to be fun ! I always thought some kind of wifi adapter would be “hacked” to make it an sdr in 2.4ghz band so I’m a little bit excited about this and what it could become. Plus I can use it for other rtl-sdr related stuff and I’m sure it’s a great buy. Thanks for posting this!

  3. AD5NL

    May need external filtering of transmitting outside the ISM bands … Also, does the 3B+ have pads for a u.fl connector? I thought I read those were being removed? Seems kinda pointless without a good antenna connection… Well except for maybe “across-the-lab dx.”

    On the other hand, what chipset does the Orange Pi H3 use? If OPi supported this… And keeps shipping with an antenna jack… It would be super awesome.

    • AD5NL

      Although I suppose one could mount the pi board at the focus of a parabolic dish… Though that seems a tad daft.

    • Freedom Bastard

      I really liked my Orange Pi Plus 2E, it is a 32bit, but much better then the raspberry pi 2 I felt because of the 2gb ram and onboard emmc and ext antenna. Now the Ras Pi4b is out with 2,4 & 8gb I would go that route, But if you can get a opi Plus2e under $40 then it would be worth it if you don’t mind the 32bit H3 environment.

Post a comment

You may use the following HTML:
<a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <s> <strike> <strong>

This site uses Akismet to reduce spam. Learn how your comment data is processed.