|Subject:||Topband: Bi-directional Beverage for DXpedition|
|From:||Ron Feutz <firstname.lastname@example.org>|
|Date:||Wed, 13 Oct 2004 11:38:12 -0500|
I need the advice of experienced Beverage builders regarding construction of a bi-directional Beverage system for our upcoming CQWW CW trip to J7 Dominica.
The antenna will be made of 300 ohm ladder line from Wireman and the transformer/termination are the K1FZ boxes.
On previous trips, a single wire Beverage was installed using an ICE Beverage transformer and termination resistor. The antenna was ~600' and pointed right at EU (broadside to US). The antenna was useful but apparently did not have the expected directivity, as it performed about as well for US contacts on 80 and 160 as did the corresponding transmit antennas.
The RG58 feed line, about 100' long, ran right to the shack with no grounding (other than the feed point and termination ground rods), or common mode suppression. The antenna had single re-bar ground rods, pounded into the rocky soil about 3' , at both ends. I suspect the ground is extremely poor, as the QTH is high on a cliff of volcanic rock. I suspect that a main cause of lack of directivity is feed line pick-up/common mode currents on the feed line.
My intention was to construct the feed lines per ON4UN's specs (pg 7-19 of his latest book). I was foiled by the inability to make the Wireman beads I bought fit on the coax (tried 2 types of coax - Wireman house brand and Belden). I had to get that stuff shipped ahead, so I just put the connectors on the lines and packed them up.
I have provided 4' copper plated ground rods, and intend to use one (or two) at the feed point, one twenty or so feet down the line, and another at the shack entrance, per ON4UN. Since the lines will not have beads, my alternative is to provide some other type of choke. ON4UN says mini coax wound on a stack of cores, but doesn't specify a manufacturer or model #. Being under time pressure, I would appreciate a recommendation on this to save me doing more homework - I have plenty more to do already.
Here are my questions:
What will give me the greatest bang for the buck (effort) in improving the antenna's directivity?
Improved grounding at the feed point? I can put out 2 or maybe 3 - 4' ground rods. Would some short radials help?
Is there any advantage to using improved grounding at the far end?
Common mode suppression on the feed lines. I intend to put a ground rod 20' from the feed point and another at the shack entrance.
Will this be effective with out some sort of choke?
What core(s) should I get to make a choke of mini-coax?
Is it practical to simply wind a choke out of RG58? If so, what are the specs.
The K1FZ system uses separate feed lines for the two directions. Do I create any problems by grounding both shields to the same ground rod(s).
Thanks in advance for the help and advice.
Ron - WA9IRV
PS Please, I know most if not all of this info is available in various archives and references. I am merely asking the opinions of experienced Beverage builders as to what will work best in this situation
Ron Feutz, WA9IRV
Air Communications of Central Wisconsin, Inc.
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