Wessex millimetric stations G8ACE G8BKE and G3PYB find a new path through the Southern Hills and make a UK record for 76Ghz.

 

1st day of September, stable high pressure and the much sought after Low humidity provided the key conditions for three stations close to the south coast of England to attempt to break the UK distance record on 76Ghz.

 

For most of the summer we have seen high humidity in the south of  England, this coupled with high temperatures ensured the moisture content in the air would attenuate the high frequency signals at 76Ghz.

 

G8ACE and G8BKE have kept a watchful eye for just the right conditions, Friday the 29th looked a good prospect, Saturday 30th even better and the weatherman said it would last.  In England!!!

The group had re-run an earlier record at 52km to prove the equipment, and we found a gap in the modest hills of Hampshire which gave a fringing path from the old WW radar site at Ventor on the Isle of Wight to a hither-to unused site near Highclere Castle near the A34.  G3PYB being of old Northern Viking stock (weekend visitor from northern Germany) volunteered to sail with the tourists across the Solent, G8ACE and G8BKE being good land fearing Hampshire sorts took to the trees near Highclere. 

 

 

The path plot looked reasonable and the distance 79km, the centre of the path near Bullington Cross had some high ground  but on K=1 we should clear the top with the very narrow beam on 76Ghz.

 

 

 

 

The dishes had narrow 3db points about 1deg or less pointing was a problem.  However we used 47ghz to set the path, signals were good but not massive, and we could comfortably used FM in 25khz bandwidth.

We had enough equipment to keep 47Ghz  running and at times 47Ghz was used for talback.                                                                         

 

 

G3PYB pictured here operating the 47GHz equipment

 

Changing to 76Ghz and correcting for small dish beam deviations produced a reasonable CW signal from G3PYBs estimated 8 to 10 mW FM Tx.   Separate TX and Rx were in use and Johns G8ACE FM Tx (3db higher output ) was found with ease and almost fully quieting.   20db at IF could be added and still have noisy but copy able FM.    G8BKE was copying signals at the same time and the contact sequence was completed with a CW exchange with G3PYB on the IOW.   Chris G8BKE was using a single HP signal diode as a multiplier from a 38Ghz TX source.    All stations used oven stabilised oscillators  on both TX and Rx. Receiver mixers were similar to the DB6NT double HP diode design (Ref .1) but with separate 38GHz multipliers from 12Ghz local oscillator chains.

 

Frequency stability was excellent which is a tribute the hard work by G8ACE with his oven-stabilised oscillators. The receiver unit were in fact transceivers, an attempt to use the unit on CW or SSB proved too much for the 79km path. Signals could be detected by placing the SSB directly on the higher power channels but signals were only just detectable in 3Khz bandwidth.   Clearly we were past the limit of a transceiver-to-transceiver capability with our equipment.

 

A key element in the success of the 79Km contact was the ability to generate the 10+mW of RF this is many db higher than the 80 micro Watts we get from the DB6NT mixers. The Russian diodes used by G3PYB and G8ACE are from the Impatt or Barratt multi junction family (we believe), and are pumped at 7.5Ghz by a few hundred mW of crystal controlled FM modulated sources.

 

Thanks must go to all stations for time and effort to build and align to equipment with only basic test equipment, and the willingness to go out on the hilltops to prove it works.

 

The contact was made at 13:15 PM local time on 1st of September over 79Km between G3PYB on the Isle of Wight and jointly with G8ACE and G8BKE  at  Sidown Hill  Highclere  Hampshire on  75976.25Mhz.

Temperature on IOW was 22deg C., RH 39%, pressure 1019mB.   Visibility approximately 25to 30km.