[Lowfer] Antenna questions

Sat, 14 Dec 2002 09:09:01 -0600

Lyle,
Your computer graphics are not there of your old "MIN" vertical.

Mike>WE0H
http://www.we0h.us/lf.html
185.3026kc QRSS-30 & CW@15wpm
ID is "WE"

-----Original Message-----
From: [email protected]
[mailto:[email protected]]On Behalf Of Lyle Koehler
Sent: Saturday, December 14, 2002 8:52 PM
To: [email protected]
Subject: Re: [Lowfer] Antenna questions

Photographs of the OK and TEXAS antennas are included in my (now rather
outdated) article on "Listening for LowFERs - Part 2" at
http://www.computerpro.com/~lyle/listen2/listn2.htm The picture of the OK
antenna also shows the gin pole arrangement that was used to raise the whole
assembly. This antenna had a top hat made of copper pipe and copper screen,
along with additional wires. What it lacked in survivability, it more than
made up for in elegance!

TEXAS had a rugged, climbable tower, but used a very lightweight top hat
structure consisting of radials made from CB whips with a skirt wire joining
the ends of the radials. Unfortunately the compressed photo on my web page
does a very poor job of showing the top hat details.

I dug through my archives and put together an article on "Lightweight
Verticals" at http://www.qsl.net/k0lr/LTWT-verticals/VERTS.HTM showing two
designs that were at least modestly successful, and which employ very
lightweight construction. The techniques used in these antennas could be
extended to top hat diameters of perhaps 20 feet. Beyond that size, I think
it would be difficult to resolve the weight and survivability issues.

If most of the antenna's capacitance is in the top hat, it theoretically
makes little difference whether the loading coil is at the top, base or
middle. But as Stewart points out, the models don't take into account the
effect of lossy objects near the antenna. To my knowledge, few LowFERs have
actually placed the primary loading coil at the top. Bill Bowers had a 1 mH
coil at the top of his original OK beacon antenna with a larger coil at the
base. BK has (I should say had, because the coil got fried by lightning last
summer) the primary loading coil at the top of a free-standing, grounded
aluminum tower. My MedFER antenna also had the entire loading inductance
just below the top hat. I personally feel that top loading would improve the
efficiency of most LowFER verticals, despite the increased coil losses
because of the larger inductance required. But I haven't solved the
practical problems of holding the coil up there.