At the meeting of the Lothians Radio Society on 24th February 2016 Brian Flynn GM8BJF talked on "3cm Personal Beacons" He wrote: "This talk looked the construction, installation and operation of the 3cm personal beacons at the QTHs of Chris Tran GM3WOJ near Tain and Graham Knight GM8FFX near Aberdeen. Both stations are quite famously well-sited and the beacons have been received at distances in excess of 500 km". He described the recent rebuild of the GM3WOJ beacon and the installation of the new GM8FFX beacon

Mostly Brian's slides (tnx)  speak for themselves, but a few notes have been added where appropriate.

 

 

 To  a microwave person the 23cm beacon (GB3EDN at Edinburgh University, King's Buildings), is "Long Wave"!

 

 

 

 

 

 

 

The path between GM3WOJ/B and GM8BJF in Edinburgh passes right over the top of Cairn Toul in the Cairngorm mountains, allowing diffraction (scatter) propagation.

 

 Amazing, isn't it!

 

 Brian's local colleague Briain GM8PKL in Edinburgh also has an excellent path to Cairn Toul.

This proved very useful later when BJF's dish was destroyed in a gale (see later)! 

 

 The beacon transmitter has a power output of ~0.5W on 10368.400MHz. The phase-locked frequency generator is on 3456.133MHz which is tripled to provide the required output frequency.

 

 

 

 View of the GM3WOJ tower after erection.

 

 Complete receive station at QTH of Brian GM8BJF in south Edinburgh.

 

Brian's QTH on the side of the Braid Hills is very exposed, and sadly the dish was blown away and destroyed in a gale during the winter of 2014/15.

 

 Briain GM8PKL to the rescue!

He agreed to host the receive station at his QTH a short distance from that of Brian GM8BJF.

The dish is solidly mounted and line-of-sight to the Grampian Mountains.

 

 

Briain's receiver is based on a modified sat TV LNB (low noise box). The local oscillator (LO) is generated externally to the LNB and fed to it via coax. The receiver has to be very stable in frequency and the LO is phase-locked to a high-quality 10MHz double-ovened reference oscillator which was manufactured in Russia by Morion.

 

 

 

Click  HERE to listen to live audio of GM3WOJ/B as received at GM8PKL in Edinburgh.

 

Click on the "M3U" button to start a download of the streaming audio. You need the Windows Media Player or some such set up to receive the audio. The audio from Media Player can be fed directly to spectran in a PC by means of a "virtual cable program" such as "V-B cable" (freely downloadable) to view it as a waterfall display. 

 

Screen dumps of the JT4 decoding program in Edinburgh.

  

 Spots of GM3WOJ/B have been reported from well-down into England.

 

 Unfortunately tree growth started attenuating the transmitted signal from the dish on the 30ft tower at GM3WOJ.

 

 

 The new beacon transmitter is housed in a light-weight ABS plastic box.

 

 

This is beacon host Chris Tran GM3WOJ himself.

 

The new installation is on a higher tower (45ft), clearing the offending (attenuating!) trees.

 

 

 

 The Doppler artefact (diagonal traces) is due to a reflection from a passing aircraft.

The beacon system is acting as a bi-static radar.

 

 

 

 

 

The GM8FFX/B hardware (also built by Brian GM8BJF) has a power output of ~1.5W on 10368.450MHz.

The antenna is a sectorial horn, giving a broad coverage of the North Sea.

 

 

 

 

Spots of GM8FFX/B have included two in Denmark.

 

 These decodes at G4CBW in Stoke-on-Trent were via rain-scatter.

 

 

For even more information, click for Brian's website: