Topband: Bidirectional vs 2 simple Beverage antennas LONG
k7tjr at pacifier.com
Sat Mar 11 13:58:59 EST 2006
Arunas and Others, This season I used several 2 wire and single wire Beverages. All of these antennas were at least 1000 ft. long. I was a little disappointed with the results but I still worked 70 new countries this year all on 160. I feel it is easier to put up a single wire Beverage and make it work with great F/B ratio and RDB factor. I tried various wire spacings for different parallel Z and found that with wide spacing like 12 inches it was very difficult to maintain a decent match for both fwd and rev directions. As most signals arrive at different angles it was very difficult to say for sure that the two wire antennas were working properly but it was my instinct that they did not measure up to a single wire but worked OK. I converted my single wire E/W Beverage to a 2 wire mid season and again I thought it no longer worked as well as it had as a single. I found that you could NOT just calculate the impedances carefully and string the wires up and have it work. It was much easier to match both directions when the parallel spacing was reduced to about 3.5 inches with a resulting Z of about 425 ohms . All tests were with the wires at 10 feet height. I used two feedlines with the unused line terminated at the switching console in the shack. I noticed a little stray pickup and mismatch due to the unused direction signals flowing into the common gnd at the switch panel and would likely terminate the unused direction with a relay right at the antenna in the future.
The bottom line to all my thoughts is that yes theory says they will work the same but. After lying on the ground sweeping the lines and changing transformer ratios, ground pegs, and etc for several days then nightime tests I feel that the 2 wire is much more influenced by imperfect grounds and terminations. Unlike the single wire it must be matched much more carefully to perform. Yes they work pretty good but be prepared to spend some time matching both directions. Contrary to other published things about 2 wire Beverages I found that it was most important to have them matched between 160 meters and 75 meters and not broadband. Most likely because they were relatively long antennas in terms of wavelength. 73es Lee K7TJR Oregon
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