Topband: Low frequency RX antenna

[K9AY]

Date: Fri, 4 Oct 2024 22:09:05 +0000 (UTC)
From: Mark Connelly <markwa1ion at aol.com>
To: "topband at contesting.com" <topband at contesting.com>
Subject: Re: Topband: Low frequency RX antenna
Message-ID: <24396951.595.1728079745347 at mail.yahoo.com>
Content-Type: text/plain; charset=UTF-8

I have a few questions about the VE3DO loop as described at:http://www.k3lr.com/engineering/VE3DO/OptimizedDOLoop.pdf

> Hi Mark ... see comments below:
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With reference to Figure 1, are the 9:1 transformer and termination resistor located close to each other, i.e. pretty much within a foot or two of each other and the center of the antenna, or is there more separation? I was guessing that for a 40 ft. top horizontal length, each of the bottom horizontals would be somewhere between 18 and 20 ft. even though not explicitly stated.
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> The feed and termination are adjacent -- either side of the ground connection, like it's cousin the K9AY Loop.
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Can the ground of the transformer just be tied over to the ground of the termination resistor without any connections to ground rods, mesh, radials etc. and, if so, can the whole assembly be elevated to at least 8 ft. base height in situations where people, animals, vehicles, yard/farm maintenance machines etc. may need to pass under? I know that Flag antennas can be deployed this way without the ground connection but could the VE3DO be also?
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> The ground connection is part of the antenna. This is what allows connection and direction reversal at the center. You can elevate the loop, but it's important to keep the ground wire vertical. 
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Has anyone looked into Vactrol remote adjustment of termination?
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> Vactrols will work, but they are temperature sensitive (including heating from operating current). They drift and require constant readjustment.
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Another scheme would be 4:1 transformers at both sides, two 100 ohm balanced lines (twisted pairs) to the operating position, a 4 pole 2 throw switch to send one side to a 2:1 balun to receiver/amp coax. for the forward side and the other side to a 0-250 ohm pot for in-shack termination control (would be transformed to 0 to 1K at the antenna). That set-up would provide pattern reversal via the switch.
The above set-up has been successfully done with Flags of reasonable size with short (under 200 ft.) feedline distances.
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> No experience with the in-shack adjustment you propose, but N4GG and others have used the 2-XFMR connection for simultaneous 2-direction RX (diversity). This requires extra care to maintain the termination impedance through the system: XFMRs, feedline, and RX imput. 
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73, Gary
K9AY


And while I'm at it....

> Tim,
> Why is this preferred over a K9AY?
> Wes? N7WS

Wes -- "Better" is what achieves your own performance goals. -- Both the VE3DO and K9AY configurations have a single, very deep rearward null. The "low/wide" shape of the VE3DO puts the null at a low takeoff angle. This should be better for DX signals. I chose the original "delta" shape for ease of installation rather than pattern, but over the years have found that its higher angle null is very good at reducing domestic (one-hop) QRM. I've gotten similar feedback from European users. - K9AY



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