Go4lo Audible SWR and Power meter Building and Accessibility Review
By Kelvin Marsh M0AID and Neil Robertson G0ORG
IT is a fairly good bet that a radio amateur will, at some stage, want to know if their
antenna is a good match for a given frequency. You could just rely on the internal ATU to make sure the radio sees a 50 ohm match, but the time will come when this is not enough. Therefore, an SWR meter will become an essential item to have in the amateur’s toolbox .
The finished boxed unit with foam packing added to keep the battery from moving
A sighted amateur may have several SWR meters, either inserted into the feedline to the antenna, or built into the radio itself. Whilst some modern radios will verbally announce the SWR reading to a blind operator, many will not, and so an external meter giving audio feedback is needed.
There have been some reasonably priced ‘accessible’ meters produced over the years, (See the evaluation of the LDG TW-1 Talking SWR/Power meter), but these have been discontinued. There are also units such as the Power Master 2 from Array Solutions that will read SWR and power when combined with a HamPod, (See the Power Master 2 review), and whilst a terrific solution, it is an expensive option and will set you back the equivalent price of a small amateur transceiver.
My interest was therefore peaked by the Go4lo SWR/power meter from SOTABEAMS. The Go4lo is supplied as a kit and plays audio tones to indicate SWR. LEDs also show power ranges below 5 watts, 5 to 25 watts and from 25 to 100 watts.
SOTABEAMS offer the name of an amateur willing to assemble and calibrate the meter, for anyone unable to do it themselves or find a friend with the necessary skills.
Neil G0ORG offered to assemble and calibrate a Go4lo for evaluation by Active Elements, and describes his experiences building the kit, below.
The many components
The kit arrived in a Jiffy bag and was well packed. The version of the kit PCB was 2.0 and marked May16. No instructions were supplied with the kit, however a full printable guide was available from the SotaBeam website. The optional hardware pack was well protected and well thought out. A small packet of sweets were included from SotaBeams proprietor Richard Newstead G3CWI, which was a nice touch.
The kit parts and the enclosure
The size of the finished meter is 110mm wide x 80wide x 40mm deep. It weighs approximately 190 grams when fitted with a 9 volt battery. The box is black and has a transparent lid, the PCB mounted LEDs are viewable through it, the only protrusions are the two BNC sockets and one momentary push switch. The transparent lid is etched with the labelling of the LEDs, the sockets, switch and other details.
Building and testing
The kit was relatively easy to construct and alignment was simple, just requiring an accurate volt meter and a good quality 50 ohm dummy load with a 5 watt transmitter. A small potentiometer is adjusted for correct voltage at two test points, the accuracy of this set up determines the overall later performance. The volt meter needs to have good resolution as the tolerance when aligning is plus or minus 0.05 of a volt. All components are conventional with no surface mount. The Microprocessor is a pre-programmed Pic device.
Photo showing the fully assembled PCB
The PCB is unusually thin, approximately 1 mm, but is of good layout and well annotated. Some of the ¼ watt resistors where a little tight to fit as the resistor component hole spacing is minimal. I had to be careful not to stress them when fitting them. From a previous career spent in the Electronics industry I have experience of fractures that can be caused to components if leads are bent to close to the component body, to make sure I did not do this I formed the leads using needle nose pliers to allow a slight return on the leads.
The fiddly bits are the Toroid transformers and the sampling coax assemblies that pass through them. These form the basis of the SWR Bridge, one for forward and one for reflected power sampling. Each toroid has a specified number of turns and the coaxial cable has to be carefully prepared as per the drawings. Once assembled I opted to hold each of the transformers in place with a blob of hot melt glue. One component to be careful with when soldering is a voltage converter marked as U1. The legs of this device are very close together and the solder pads are very, very close together.
The LEDs lit during Testing
The PCB mounts on the lid and the PP3 battery is inside the unit, it has a typical battery snap connector lead which is directly soldered into the PCB. Careful removal of the battery when changing it is needed otherwise over time the soldered wires may break at the solder joint.
It may have been better for SotaBeams to have supplied a Molex type two pin connector and header to help with durability here when changing the battery. Care is needed to do so and is quite fiddly.
The battery is located between the PCB and the end of the enclosure to this end the battery has space to rattle around (and jiggle the connector wires). As the device is also intended to be used portable I think a small piece of foam between the top panel and the battery side is a worthwhile addition.
Observations and further ideas
For those with sight difficulties the recommendation would be to get help changing the battery although for permanent use I don’t see why a 9v regulated mains adaptor cannot be used. There is enough space to add a power connector to the enclosure if required.
If the PCB were added to a different hardware box then coaxial leads could be used to connect to SO239 connectors, if required.
There is scope to add a further sound modification if required in place of the 3 power LEDs for the sight impaired, this could be a further tone to indicate some approximation of power level however the levels would remain an approximation as the power resolution between each LED is quite large.
For those who want to measure power exceeding the 110w level (400w for example) there is scope to make a new SWR sampling head and modify to the PCB. The only restriction is that careful modification will need to be made to handle the plus or minus voltage within the maximum voltage tolerances required to create the comparison error measurement. As it is a microprocessor circuit then it would probably be prudent to shield the PCB from the SWR sampling head and use feedthroughs for the voltage measurement connections at these power levels.
Conclusions regarding building and testing the kit
The kit does require a level of skill to construct, especially the transformers and sampling coaxial cable. Some solder joints are close together so good soldering techniques are required. If in doubt I recommend the use of a test meter to check for any solder bridging.
You can hear an audio demonstration of the Go4lo in action here.
Click here for Go4lo MP3 audio demonstration
I think Richard Newstead from SotaBeams has provided a great little item here that has visual impaired accessibility built in, possibly without realising it.
Although aimed at the portable market for SOTA it is ideal for visually impaired Amateurs as the sound is the most important element in this instance. The kit is priced correctly and has been well thought out. All items are of good quality and it was a pleasure to construct. As the clever bit is the Microprocessor there is scope to modify it if needed for further ease of use by visually impaired Amateurs.
The device is useful to any Radio Amateur, during testing I appreciated how quick it was to find a drop in SWR when using an antenna tuner. The unit is very accurate and overall a pleasure to use.
Further notes on usage
Holding the oblong box with the BNCs at the top, the left one is Transmitter and the right is the Antenna. Just below the two BNC in the middle of the box is a power switch, the unit powers on with a dit dah and powers off automatically with a dah dit a few seconds after no use or if it has not seen any RF.
The power up time can be short if the transmitter is not activated but if it goes off a simple button press puts it back on again. On power up the red SWR LED blinks then goes off, nothing else is displayed. When power is applied the appropriate power LED, green for 0.25 to 5 watts, orange for 5 to 25 watts or red for 25 to 110 watts light. The red SWR LED flashes in line with the beeps of the measured SWR. Sotabeams claim that the pp3 9v battery will last over a year as in standby it only draws a few micro amperes.
From Sotabeams product information:
Our latest product is something that I have wanted to develop for a long time: it’s an audible SWR-Power Meter. Unlike conventional SWR meters, the Go4Lo indicates SWR by sound. Basically the worse the SWR, the faster it bleeps.
This type of user-feedback makes it much easier to adjust antennas than using conventional SWR meters. If you want to know actual SWR, it is just half the number of bleeps per second (e.g. six bleeps per second = an SWR of 6/2=3:1). To make tuning even easier, the tone of the bleeps reduces below an SWR of 2:1 too giving additional feedback: this SWR meter really lives up to its “Go4Lo” name.
In addition to the audible feedback, we built in two types of visual feedback. Firstly the SWR is indicated by a flashing LED which flashes at the same interval as the SWR bleeps. But that’s not all as we incorporated a three-stage power meter showing 0.25-5 Watts, 5-25 Watts and 25-100 Watts. The transition at 5 Watts is especially useful for QRP operators as it makes setting your power level accurately to 5 Watts, simple.