Setup 3 below was retained (Tx antenna and 120m long beverage feed location are
still 120m apart ) but
the 160m inv L Tx antenna was converted into a quarterwave 80m vertical over
the same radial wire field.
The isolation on 80m measured 44dB. (on a freezing day)
73,
Michel, ON7EH
From: Michel Spelier
Sent: Tuesday, January 27, 2015 10:29 PM
To: topband@contesting.com
Cc: on7eh@skynet.be
Subject: Antenna isolation measurements
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
trasnformer). 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 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 much better Bev grounding than above. (added
2nd grounding bar and longer, more ground radials)
Bev length increased to 120m & inter-ant distance again 120m.
Isolation: 43dB.
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)
We hope these measurements provide sufficient detail to be of help for others.
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 also 50dB)
73,
Michel, ON7EH
_________________
Topband Reflector Archives - http://www.contesting.com/_topband
|