CQ's July issue had an article on a horizontal loop.
It was entitled" Remote tuned Loop for HF DX"
The article pulled no punches on the difficulties of matching this
antenna on different bands. The article addressed a "160M square
loop" and had the following table of impedances:
1.8 MHz 75-10j impedance
3.8 189+213j
7.15 331-413j
10.1 2395-330j
14.2 550-696j
21.3 1079-691j
28.5 1163-194j
I would imagine that these impedances would roughly scale for loops
designed at lower primary frequencies.
Most of the article was devoted to the design of the remote tuner
required to match this antenna.
Bottom line: If you intend to use this type of antenna effectively,
you better figure out how to remotely tune it.
73 de Brian/K3KO
Pete Smith wrote:
>
> Hi Tim -- just for fun, I modeled a square full-wave 80m loop at < 1/4 wl
> high -- 15m up at 80m. It's true that the peak radiation from such an
> antenna on its fundamental is straight up, but the radiation at 23 degrees
> elevation, which is a good approximation of the takeoff angle of a high
> dipole or 4-square, is only 8 db down from that straight-up peak.
>
> Even more to the point, the signal is 5 dB better at that angle than a
> somewhat idealized 1/4 wave ground-mounted vertical over real ground. With
> the usual sort of radial system, one might regain 3-4 dB of that, which
> still makes the loop look like a pretty decent performer. This situation
> even pertains at least down to 10m in height.
>
> On the higher bands, the antenna has a fair amount of gain at useful DX
> angles (at least on 20m and above) even at the lower height. The trouble
> is that it also develops some pretty deep nulls. With modeling, you might
> be able to place them usefully just by moving the feedpoint around the loop.
>
> So my conclusion would be that, particularly in a case where you have
> adjoining power lines or some other constraint on a high antenna, the
> horizontal loop has something to recommend it.
>
> There is another interesting variation on the theme, called the N4PC Loop.
> It is 51 feet on a side, fed in phase at opposite corners, and at 50 feet
> height it produces a better pattern by a few DB on 80, and has fewer nulls
> on the high bands as well. The added feed complexity might be worth it.
>
> 73, Pete N4ZR
>
> List Sponsored by AN Wireless: AN Wireless handles Rohn tower systems,
> Trylon Titan towers, coax, hardline and more. Also check out our self
> supporting towers up to 96 feet for under $1500!! http://www.anwireless.com
>
> -----
> FAQ on WWW: http://www.contesting.com/FAQ/towertalk
> Submissions: towertalk@contesting.com
> Administrative requests: towertalk-REQUEST@contesting.com
> Problems: owner-towertalk@contesting.com
List Sponsored by AN Wireless: AN Wireless handles Rohn tower systems,
Trylon Titan towers, coax, hardline and more. Also check out our self
supporting towers up to 96 feet for under $1500!! http://www.anwireless.com
-----
FAQ on WWW: http://www.contesting.com/FAQ/towertalk
Submissions: towertalk@contesting.com
Administrative requests: towertalk-REQUEST@contesting.com
Problems: owner-towertalk@contesting.com
|