A new distance record of 102km was achieved on 76 GHz Saturday 14th September 2013, a contact between Batcombe Hill, Dorset (IO80RT59) and Eglwysilan Mountain, Gwent (IO81IO36). This is also believed to be the first 76 GHz contact between Wales and England.
Operating on three mm-bands, 24, 47 and 76 GHz, 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.