Re: Topband: Antenna isolation measurements (3)
To complete this winters' measurement session, Elecraft's Gary Surrency quoted +33dBm (=2Watt) to be the max input power the K3 handles, prior to a (T)RX-failure. (TR-switch PIN diodes and/or post mixer IF AMP) A LCD warning is also issued: HI RFI for "too high RF input". I.e. our 100W will deliver on 80m, +6dBm (=50-44) at the ext Rx input. A safe enough value on both 80m and topband, leaving some margin for further setup optimisation if there is an answer to the following question: Is there a minimum target Tx/ext RX-isolation value (in dB) guaranteeing minimal noise coupling from the Tx-antenna to the Beverage? Why? By bringing the Beverage feed somewhat closer to the (fixed) Tx antenna, the (unterminated) Beverage length could easily be extended, improving its directivity. This isolation is an easily manageable quantity here allowing for better Beverage position trade-offs on the farmers'field. Tnx es 73, Michel, ON7EH -Original Message- From: on7eh Sent: Wednesday, February 04, 2015 10:37 PM To: topband@contesting.com Cc: on...@skynet.be Subject: Re: Topband: Antenna isolation measurements 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: on...@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 _ Topband Reflector Archives - http://www.contesting.com/_topband
Re: Topband: Antenna isolation measurements
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: on...@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
Topband: 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 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
