Prior to the CQWW160, we did some (topband) antenna isolation measurements between: -a quarterwave inv L (top at 15m down to 11m) and -a new unterminated beverage (0.8m high) of different lengths (via a 9:1 transformer) and 2 different locations. The Bev used PVC-covered 0.6mm thick twisted pair telephone cable.
The power source consisted of the K3 (with its integrated wattmeter) feeding the inv L tru a remote-fed CG 3000 ATU. The rx was a spectrum analyser connected to the Bev. The very broad "main lobe" of the inv L was pointing to the Bev in all setups. Setup1: Bev length=120m & inter-ant distance=35m (distance between inv L feed and Bev transformer) Isolation: 33dB. Conclusion after A/B-switching on the K3 Rx: no improved Rx noticeable (high noise) and ext Rx input at risk. (too high input level) Setup2: New location Bev length=75m & inter-ant distance= 120m Isolation: 50dB. Conclusion after A/B-switching on the K3 Rx: still no improved Rx noticeable but low enough input level not to use a frontend saver. Setup3: Same location as above but with improved Bev grounding compared to Setup2. (added 2nd grounding bar and longer, more ground radials over the four 5m ones) Bev length increased to 144m & inter-ant distance again 120m. Isolation: 43dB. Conclusion: the S/N of the Bev is much better than the Tx/Rx inv L for the expected heading, even signals out of the general bearing have better S/N, others are not audible or much weaker. (expected behaviour from its radiation pattern) Setup3 was successfully used last weekend during the CQWW160CW. It was the first time, a dedicated Rx antenna was put to use. The isolation measurement on Setup3 was done 2 days after the contest without apparent impact to the K3 ext Rx. (we expected <=50dB and not 7dB less) We hope these measurements provide sufficient detail to be of interest for others. 73, Michel, ON7EH _________________ Topband Reflector Archives - http://www.contesting.com/_topband
