Beacon Composition
The beacon consists mainly of six modules:
- Micro controller (Chinese STC8G1K08A, a cheap Intel8051 clone)
- SI5351 frequency generator
- Driver amplifier board
- Power amplifier board and low pass filter
- Regulated power supply
- GPS antenna
Description and function of each specific module
1. The micro controller controls and drives the si5351 generator board which produces the desired frequencies and functions. (Arty’s territory)
2: The si5351 is a very versatile chip and is used in many projects where signal generation is required. The commonly used and readily-available breakout boards with the si5351, can be obtained very cheaply through various sellers on the internet. The si5351 can generate signals from about 10Khz to over 160Mhz.
In this design the si5351 generator provides a low-level RF signal followed by a simple 50Mhz LC bandpass filter, which is then amplified by the driver amplifier board.
3: The driver amplifier board is a very popular WSPR RF amplifier among QRP enthusiasts. It consists of two transistors in cascade as shown in the attached schematic. It produces about 200mW of RF output power which is enough to receive worldwide WSPR decodes on the HF bands.
4: The power amplifier is driven by the driver amp and amplifies the signal to about 5 watts PEP. The power amplifier uses a single power transistor (BLU99) which was designed by Philips as a UHF FM amplifier for commercial use. In this case, the transistor has been biased to class AB to achieve good linearity and it’s performance at 50Mhz has been satisfactory, a much lower frequency for which it was designed. The power amplifier is then followed by a 7-element low pass filter to filter out any harmonics.
5: The power supply is a conventional setup using a mains transformer, full wave diode rectifier and a 4700uF smoothing capacitor followed by a 12 volts single unit regulator. A second 5 volts regulator is also included to provide power to the microprocessor and the GPS Unit. The power supply is protected by two fuses; a 350ma on the mains supply and a 2amp fuse on the 12v supply rail. The total current consumption of the beacon is around one amp.
6: The GPS unit provides control for the WSPR timing, where precise timing is of utmost importance. The GPS unit is an external sealed unit and is remotely connected by a series of cables to the main beacon unit. It has been installed on the roof of the Club’s Shack for the reception of GPS orbiting satellites. A red led on the beacon front panel indicates the GPS lock and the blue LED indicates the time synchronization of the GPS. The white LED works by taking a sample of the RF being radiated and therefore indicates the RF output power.
Building the Beacon
The beacon project started as an experiment by Arty SWL, where he demonstrated how the microcontroller and the si5351 can be used as a beacon for CW and WSPR simultaneously. The si5351 output was enough to receive the signal on the Club’s radio.
Having personally built the previous 6m CW beacon back in 2012, I thought it was time to upgrade the system to the digital era while still use it as an analogue CW beacon. With Arty’s software programming expertise it was now possible to build such a device.
The beacon started being built in late January 2026, by initially building the driver amplifier board. It worked well when driven by the si5351.
Later, Domenic (9H1M) donated a couple of transistors towards the project, including the Philips BLU99 power transistor, following which, work with the power amplifier proceeded.
The power amplifier used was a design by DK7ZB which he used in his 6 to 10m transverter project. I used only the PA part of his project and substituted the transistor by the BLU99. The design worked perfectly and was producing a good output.
When tested at the Club with the test equipment provided by Stephane 9H2WB and Domenic 9H1M, the beacon proved to be working superbly with very low spurious or harmonic content (picture included).
The Antenna
The antenna chosen was a Squalo, mainly a square loop designed by PA3EGH.
It is designed for horizontal omnidirectional radiation and is basically a square folded dipole. It is made from 12mm copper pipe with 8 elbows. A very detailed description of how to build it can be found on You-Tube by searching 6m Squalo.
The antenna was also a group project: Albert 9H5AP provided the materials, Ezechiel 9H2EZ welded all the elbows, Manuel 9H1GW worked the insulator on a lathe and I was responsible for the necessary assembling and tuning. The Squalo tuned very well without much hassle with near perfect SWR on the required frequencies.
Parts and donations
Thanks to the generosity of the Club Members, much of the parts were donated by MARL members. A big thank you goes to Edgar 9H5OO for donating such an awesome enclosure, Domenic 9H1M for cables and an endless list of parts, Stephane 9H2WB for cable and other parts, including the provision of tools and equipment.
Manuel 9H1GW for the insulator and Arty SWL for providing much expertise.
Last but not least, my trusty and generous junk-box for providing most of the other required parts.
Stephen Vella
9H1SV