[PVRCNC] 4 el 160M quad at I5JVA

Sun, 6 Oct 2002 14:03:56 -0400

Interestingly, or not, there are difficulties with delta loop arrays
that manifest themselves in "yagi" configurations. What they are
showing at that url is not a quad.

A two element delta array works decently because the closeness of the
reflector causes more current to be induced in the upper than the
lower, mimicking the current in the DE.

But it is increasingly difficult to get the far elements in a larger
delta loop array to work right because of the need to get more extreme
current phase angle shifts in an element as it gets farther away from
the DE.

Also the shape of the element causes a region of opposite current at
the lower end of the vertical sides. This causes the element to have a
lower acceptance of induced energy from the DE.

The quad does not suffer this fate because a quad element has equal,
mirroring, current in the upper and lower portion of the loop,
regardless of whether it is diamond or square configuration. The
current in the top half produces in phase excitation to the bottom
half, which adds to, rather than opposes the induced current in the
bottom half.

There is probably not that much difference between the two directions
in the illustrated delta array if the forward elements are parasitic.
The way to make a 4 element delta loop work is to feed, balance and
phase the forward elements.

The difference between optimal two and four element parasitic quads is
quite noticeable.

Just cause something is a lot of wire, doesn't mean it will work.
Actually, on the whole, wire parasitic arrays are a lot harder to do
than traditional aluminum tubing yagis.

Design aggravations include end effect of insulators and fastening
loops at wire ends, antennas closer to ground relative to wavelength
making design specific to height, getting spacing and orientation
correct, hyperbolic distortions of the "ideal" element shape caused by
gravity.

We investigated the delta loop very early on for use in the wire
monster and had to let it go for cause.

Guy.

----- Original Message -----
From: "alsopb" <[email protected]>
To: "PVRCNC" <[email protected]>
Sent: Sunday, October 06, 2002 9:24 AM
Subject: [PVRCNC] 4 el 160M quad at I5JVA

> Try this link.
>
> N4AF is this your next project?
>
>
http://www.contesting.com/data/spotlight/images/b2605ce1c1d4d276470f2c
3490d12d38.jpg?contestingsid=8e361c73500c6c49c03c1362a7186a87
>
> Interesting that no real pictures are provided.  As K2AV pointed
out:
> "How does one photograph invisible wires?"
>
> 73 de Brian/K3KO
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