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
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
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