G3PHO/P on 47GHz

In 2004, I was fortunate enough to purchase the 47GHz portable system belonging to David, G0IVA, who had decided to give up the millimetre bands after a change of location from IO83 square to IO84!

This equipment had already achieved a great deal for David, culminating in a UK 47GHz DX record back in 2001. So now I had the honour of taking over this gear, with every intention of extending that record even further one day! David,as GW0IVA/p, is shown here right, on the 1085m asl summit of Snowdon in North Wales(IO73XB18) when he made the UK record with GM0HNW/P and GM7MRF/P located on Cambret Hill in South West Scotland (IO74UV34).

David had wisely built the 47GHz gear to be as lightweight and as transportable as possible since he had to carry the whole station,plus 144MHz talkback, in a rucksack (see photo above) to mountain tops. I had different ideas and so set about modifying his system a little, particularly in the field of interconnecting cables and tripods. Whereas David had to use very thin, individual wires for interlinking the modules and battery, I was able to make these a little "beefier" and included "bomb proof" connectors because I intended operating from by the side of a vehicle. Backpacking might come later!

Apart from the transmit oscillator source, the whole RF system was well built by G0IVA from DB6NT kits and designs. The specially milled feedhorns shown in the photo below are of particular note.

The photos above and right show what I did to strengthen the 47GHz system. First of all, I mounted the whole thing on a wooden platform and a strong National tripod(from my old 10GHz portable setup!) and changed the individual flimsy DC wires to thick multiway cables with XLR or coaxial connectors at each end. This enables a very quick assembly on arrival at the portable location. The photos also show the orignal large diecast aluminium box that houses the crystal controlled ovened transmitter oscillator. I added the DC connectors and sprayed the box with silver Hammerite paint.The box houses a DF9LN OCXO which is quite stable and "clean" by the time it's multiplied to 47GHz from around the 100MHz starting frequency! The box outputs at just below 12GHz and this is then multiplied by a DB6NT multiplier/doubler (the module underneath the aluminium plate on the dish feed arm)to just over 23GHz and is then doubled in the final multiplier to produce 22 milliwatts of 47GHz at the TX feedhorn.
On the left is another view of the modules. The receiver consists of a DB6NT 12GHz local oscillator driving a doubler to 23.5GHz and then into a separate DB6NT sub harmonic mixer. The 12GHz oscillator module can be seen in the photo above, held to the mounting plate with two aluminium straps while the 23GHz doubler and subharmonic mixer modules form the topmost units in the photo to the left. In this photo, the right hand feedhorn is for receiver while the left hand one is for transmit. TX/RX change over involves pivotting the required feedhorn around a wing-nutted screw that holds the whole TX/RX assemble to the dish feed arm or boom... no fancy (and lossy) relays at 47GHz!

With this equipment I have been able to get out on a number of portable contests over the past two years and managed to win the UK Microwave Group 47GHz Cumulatives in both 2004 and 2005.My best DX so far, at just over 100km, cannot compare with David's UK record but I'm working in it! I have made many contacts at distance between 90 and 100km. FSK CW seems to get through best but NB FM is used when the signals are strong.

The photo on the right shows me as GW3PHO/P on the Blorenge in SE Wales during the September 2004 24 & 47GHz Cumulative Contest. The larger tripod and dish are for 24GHz.

Thanks, David, for letting me have your 47GHz gear! I hope I can put it to good use and fly the 47GHz flag up here in the North of England for some years to come!