BOXA-SWR High Performance VSWR Bridge

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High Performance VSWR Bridge

The BOXA-SWR is a high performance VSWR bridge. It has been designed for the sort of user that wants to develop their own remote display using Microchip PIC, Raspberry Pi, Arduino or just a standard meter! The BOXA-SWR uses a dual sampling system for good HF performance and easy adjustment.

The RF side is fitted with BNC sockets. The output is via a USB-B socket [photographs show protoype with D socket]. Outputs are analogue DC voltage and are fully adjustable to suit your meter or analogue-to-digital converter.

Downloadable assembly instructions


Board size 80 x 55mm (four mounting holes pre-drilled)

Enclosure size 65W x 86D x 30H

Weight (in enclosure) 150 grams

Power 2 - 100 Watts (VSWR accuracy reduced below 5 Watts)

Frequency range 1 - 50 MHz

Through loss < 0.1 dB @ 30 MHz

Return loss > 28dB @ 30 MHz  (>24 dB @ 50 MHz)

Directivity > 25dB (1 - 30 MHz)

[all measurements on pre-production unit using calibrated network analyser]

A Note on SWR Bridges

In developing the BOXA-SWR I had to research a number of bridge circuits. I built and tested a few too. My conclusion was that the only one that produced sufficiently reliable and reproducible results was the Tandem Match. That's why I use it for the BOX-SWR. One of the nice things about it is that it requires no setting up to achieve good directivity. It also seems to produce better readings at high VSWRs than other bridge circuits.

BOXA Products

All BOXA products are available in three configurations:

1. Board kit: a high quality PCB with all components. Board has mounting holes for you to install it in your own enclosure.

2. Board kit plus enclosure: adds a high quality rugged aluminium enclosure complete with laser-cut front and back panel.

3. Fully built and tested: the complete product with enclosure, built and tested at our factory. Ready to use.


6 Reviews Hide Reviews Show Reviews

  • 3
    could use better documentation

    Posted by Jurgen ON5MF on 28th Sep 2016

    The quality of the kit is very good but the documentation does not show the pinout of the new USB connector.

    The output voltage is not linear to the tx power so you have to calibrate your measurement before you can calculate the SWR.

    These are some of the values for my kit:
    100W is 4,20V
    75W is 3,06V
    50W is 2,20V
    10W is 0,94V

  • 5
    Lovely Kit

    Posted by Andre ZL2ATL on 15th Aug 2015

    It arrived very quickly and was well-packed. The quality is good and was a good choice for my plan to design a digital display to add to it.

  • 4
    BOXA-SWR SWR bridge (Kit)

    Posted by G4FAT on 30th Jul 2015

    Generally excellent quality and works fine. The circuit details need updating to reflect the change to a USB-B socket. (Plugs aren't easy to get hold of, either).

  • 5
    It is for checks less than 1w.

    Posted by Yoshio JH1DIS on 8th Apr 2015

    I purchased pre-assembled and kit. 
    Kit for my low cost SDR (AE9RB Peaberry SDR 2).
    I add Arduino FWD shield and LCD shield .
    It became able to measure RF power less than 1W. 
    FWD Shield is using LMC6032IN op amp .(lot of sample in the internet)
    The measurement maximum of FWD: 10W.
    Finally this kit is great.

    Arduino Software is the voltage measurement software. There is a lot sample in the Internet.
    pre-assembled one for outdoor use with FT-817.

  • 4
    REmote Head for FOxDelta SWR3

    Posted by G3UFO on 25th Feb 2015

    I wanted a dual feed remote head for my FoxDelta SWR3 meter.
    The SOATABEAMS unit fitted the bill exactly. And was very easily interfaced.

  • 5
    VSWR Bridge - Pleasure to build

    Posted by Martin Waller - G0PJO on 28th Dec 2014

    I was lucky enough to receive a SOTABEAMS HF VSWR Bridge kit for Christmas. Christmas being Christmas my soldering skills were not up to the job on Christmas Day or Boxing Day so the build was delayed for a couple of days. Before building the kit I printed off and read the instructions, it all seemed to be very straight forward and I foresaw no problems. Opening the kit revealed that all parts were easily identifiable and complete. I followed the instructions to the letter and took photographs at every stage. As you would imagine the most intricate part of the build was winding the coils and cutting the small length of coaxial cable as required. The build took around one and a half hours which included time to make copious cups of tea! I calibrated the bridge using my FT-817ND connected via the bridge into a dummy load. At 5 watts I got a reading of 0.645 volts each way which I’m happy with as I plan to interface the board to an Arduino ADC pin which has a maximum input voltage of 1.1 volts.. On the whole I’m very pleased with the device. My only comment would be about the use of a 9 PIN connector. I feel that a simple 3.5mm stereo socket would have been easier as most people have such plugs to hand or possibly just a 3 pin header connection. So, I'm off to do some programming now to see if I can turn the kit into a simple digital VSWR meter.

    [Thank you for your review Martin. The new version of the kit uses a USB connector rather than a 9 pin socket.]