ARLA/CLUSTER: Batido recorde de distancia em 76 GHz no Reino Unido

[João Costa > CT1FBF]

 New UK 76GHz distance record

A new distance record of 102km was achieved on 76GHz Saturday 14th
September 2013, a contact between Batcombe Hill, Dorset (IO80RT59) and
Eglwysilan Mountain, Gwent (IO81IO36). This is also believed to be the
first 76GHz contact between Wales and England.

Operating on three mm-bands, 24, 47 and 76GHz, were *Chris Towns G8BKE* and
*John Hazell G8ACE* at Batcombe Hill and also on the three bands at
Eglwysilan was *Ian Lamb GW8KQW*, and with the valuable assistance from *Keith
Winnard GW3TKH* who was also operational on 24GHz.

All three bands were worked using NBFM with full duplex operation on 76GHz
between GW8KQW and G8ACE with one way FM between G8BKE and G8KQW. Signals
on 76GHz were exchanged for over two hours with a very gradual increase in
average signal strength after some QSB initially.

Both Tx and Rx were locked using RDDS PLLs at G8ACE and the GW8KQW Tx RDDS1
locked. This was the first time RDDS locking was used at both ends and
meant the 76GHz signal was acquired within seconds due to the highly
accurate frequency control therefore no tuning required. References used
for the PLLs were 10MHz double oven OCXOs which are readily available on
ebay.

It has been very difficult to improve on the previous record distances
primarily due to the earth being curved. So far if the path is not optical
then it doesn't work, none of this K=1.33 stuff on 76GHz with the
relatively low power levels used.

This tremendous success is a result of continual innovation and systematic
improvements and testing of the equipment built and used by the Wessex
microwave enthusiasts with support from other microwave radio enthusiasts
in UK and Germany.

By calculating the link budget and path loss of this path it was possible
to predict what environmental conditions would potentially give sufficient
margin for success. The 7 day weather forecasts (specifically the dew-point
temperature) have been analyzed for several weeks whilst waiting for the
optimum conditions to materialise.

We are indebted to Keith GW3TKH for the suggestion of this path which is
LOS and for his assistance in guiding Ian G8KQW up the Welsh mountain,
without Keith’s suggestion and support this would not have been possible.
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