SOTAbeams Go4Lo SWR-Power Indicator kit

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The SOTAbeams Go4Lo in action.

Adrian PA0RDA heard about the SOTAbeams Go4Lo SWR-Power Indicator. Since it has an audible SWR indicator, it sounded interesting for blind operators. So he ordered a kit and asked me to build it. This article discusses my findings regarding this kit.

The first received kit was an old version and had some issues/missing parts, so SOTAbeams sent new parts, making it the Go4Lo II. This device is designed for portable usage, e.g. for the Summits-On-The-Air program where radio amateurs climb hills/mountains and make radio contacts from those summits. The power indicator tells you weather you’re transmitting QRP (below 5 watts). The SWR meter produces beeps, less beeps per second means lower SWR.

Kit contents

The kit consists of a plastic case, a rather thin PCB and all required components. The PCB seems to bend a bit. The pads for the resistors are rather close, so you can’t use a bend tool. Besides that, the PCB is professionally made, including coating, silk screen and through-hole pads. The case consists of a black box and a transparent cover. No drilling or labelling is needed, since all required holes and text is already done using a laser cutter, resulting in a professional looking front.

The building instructions are not included, but can be downloaded from the website, which means you’re always using the latest available version. The document suggests it’s not ready yet, since it starts with a “SECOND DRAFT ONLY” heading. The document includes an image of the PCB which shows you where to place which component, although the resolution is rather low, which makes some references hard to distinguish.

The circuit is rather easy: a 3.3V voltage regulator circuit, a push button, some LED’s, a coil based bridge and a PIC-processor which brings all these things together. All the smart stuff is in the software, which seems to be proprietary (I couldn’t find any source code). There is no documentation on how the circuit actually works, which is a pity for beginners; they should learn how to read a circuit. The circuit is not included in the building instructions, but can be downloaded separately from their website.

Building

The building instructions start with building the bridge, especially the coils you have to wind yourself, and two small pieces of PTFE coax that run them. The pictures display the correct placement and give you a clue about the construction. However, the documentation on how to wind the coils is lacking details: it doesn’ t tell you in which direction the secondary part has to be wound (which is not critical b.t.w.) and people might not know what “23 windings” means. If you don’t know either… it’s the number of times the wire goes through the hole of the coil. It’s always important to give good instructions on winding coils, otherwise beginners will end up with questions or cancel their project.

Apart from the coils, the remainder part of this kit is rather easy to build. The order in which you place and solder the components is rather straightforward, although I would suggest not to start with the coils. Most resistors have 5 coloured rings, so be sure to use an ohm meter to verify the resistor values. Also use a small soldering tip, the pads are a bit small, and the pads for the voltage regulator are very close together.

When all components are placed and you’re quite sure there’re no short circuit, it’s time for the smoke test. I also verified the output voltage on the regulator, which was exactly 3.30 Volts.

The documentation gives a clear procedure on how to set the two variable resistors. However, for a correct calibration you need a transmitter that produces exactly 5 watts. Most transmitters do have a very inaccurate output power, regardless of the setting. So if you have a power meter, simply use this to set your TX to 5 watts precisely.

I tested the transmission loss with my MiniVNA, within the supported frequency range (2-50 MHz) the loss was less than 0.15 dB.

Usage

The usage is very simple. Just connect your TRX and antenna to the box, apply power, press the button and check the readings. The audible SWR meter works very nicely, which was the actual reason for building this kit.

The device has BNC connectors. Most shortwave radios use PL connectors. The reason for choosing BNC is because the producer focuses on QRP and portable usage, for which BNC is more common.

Conclusion

Although it is not a very difficult kit to build, I can’t tag this kit suitable for beginners, merely due to some missing details in the documentation which are essential for those people. Apart from that, SOTAbeams has done a very nice job by bringing out this kit. The device itself is light and easy to operate, and suitable for QRP and portable operations to check if your antenna is OK and your transmitter actually produces output.

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The SOTAbeams Go4Lo in action.

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