A Simple VHF Beacon

Completely inspired by an article by Steve Macdonald (G4AQB) in Practical Wireless (Feb 2026), one of our Club members decided to build the simple VHF beacon. It takes the minimum of components to create but there's still quite a lot to get it right.

Fortunately, at least for our intrepid builder, he already had all the individual parts needed - basically an Arduino Nano and an accompanying Si5351. The code for the Arduino is downloaded from github and uploaded - note that you will need to amend the code to suit your setup.

Code Amendments

First off, the message and frequency output need to be set. This seems easy enough, but please do not just accept that whatever frequency you set, is the frequency that will be transmitted on! This is because your Si5351 module will need to have its calibration factor set. You can download the calibration code from github here, and ideally you'll need a frequency counter to do this.

Finding the appropriate calibration factor for your Si5351

Once you have your calibration factor, you can enter this into the beacon code. You should also carefully choose your frequency... the Si5351 will operate up to 160MHz, so easily covers the 2m band - but you could also try out 70MHz or 50MHz (but will need to amend the LPF to suit).

In the 2m band plan, there is a frequency allocation for personal beacons; this runs from 144.491 to 144.493MHz. You will not need to apply for a NoV to run this beacon and as it is (well) under 5W, it can be left on all the time - but please do not be tempted to use it without an LPF!

Low Pass Filter

The 2m LPF was built on to a 25mm square piece of double-sided PCB. This had a central track cut into it, so that SMA connectors could be soldered on at either side. The middle of that central track is cut out and the inductor soldered across it, with a 22pF capacitor at either side.

In the article, three turns of 28swg were used, wound around a 7mm drill bit. However, a 7mm drill wasn't available (but a 6.5mm drill bit was) and the wire used was of an unknown gauge but presumed to be about 28swg!

Adjusting the 2m LPF using a NanoVNA

With a NanoVNA calibrated for 120 - 450MHz, the S21 port is used to measure the logmag and SWR. This allows us to find the insertion loss and to see how much the 3rd harmonic is reduced by. These figures can be tweaked by pushing and pulling the turns of the inductor. The image above shows a 0.2dB insertion loss and the 3rd harmonic is down by -32dB.

In Use

Once the parts were assembled, and soldered on to a 1/2 size breadboard, the unit could be powered via the USB connector, or via a 9v PP3 battery (connected to the Vin pin on the Nano). This will allow the beacon to be taken out and used /p, trying it out from different locations.

So, how did it fair? With barely 10mW into a colinear aerial, it was heard over an obstructed path a little over 5km away. It was still a strong signal from over 3km away... but the best yet was hearing it on the Wessex websdr (transmit frequency: 144,491.500kHz) which is 24km away!