The GM8FFX 10GHz Beacon.

Brian Flynn  GM8BJF

Background

I met Graham Knight GM8FFX at a local rally last summer. He told me he was back on 2m and had been working Chris Tran GM3WOJ. He mentioned that Chris had told him about the 10 GHz beacon I had built to put on at his QTH near Tain and in passing Graham reminded me that there was a proposal back in the mid/late 1970s to put a 10GHz beacon on from his house south of Aberdeen. This never came to fruition for reasons that are now lost in the mists of time and he asked if I had thought of putting it at his QTH. I said that I was willing to put together another personal beacon for his place. Graham has an outstanding VHF/Microwave QTH with a clear view over the North Sea and consequently a sea path to PA0 and East Anglia. In November 2014 I visited Graham and the subject arose again and I agreed to go ahead building the hardware. We also decided that a suitable spot to mount it was on a pole supporting his HF antennas. Over Christmas and New Year I built up the hardware and tested it.

Hardware

The transmitter uses a TI LMX2541 FracN synthesiser chip programmed by a PIC to generate a signal on 3456 MHz. The frequency of this is multiplied by three to give an output on 10368.450 MHz. The output of the multiplier is filtered and amplified in the Tx side of an Eyal Gal up/down converter unit which gives about 1.5 Watts at the horn antenna. The modulation is FSK and JT4G and it sends its callsign and QRA.

Figure 1: Beacon block diagram.

The vital statistics of the beacon are:

Callsign                 GM8FFX

Location               IO87WB

Mode(s)               JT4G + FSK

Frequency            10368.450 MHz

Reference             DOCXO (Usually within 100Hz of nominal carrier frequency)

Power                  1.5 W

Antenna               Sectorial Horn

Beamwidth           ~45  degrees

Beam heading       ~165 degrees

JT4G timing           GPS

Reception Reports

To date the best DX spot is from G4KUX in Co Durham at 271km, but with a tropo lift I would expect that it may get further. All reports of reception will be welcome. It can be heard in Edinburgh on high spots which are clear towards Aberdeen.

Figure 2: Close-up of the White box, the horn and the GPS antenna.

Figure 3: The beacon installed at Graham’s QTH.

Figure 4: Another view of the installation.

Figure 5: The take-off to the south.

Acknowledgements:

Mark Hughes GM4ISM – donation of Alcatel White box case

Graham Knight GM8FFX – the location.

Andy Talbot G4JNT - for doing the hard work sorting out the JT4G coding.