TopBand: Inverted-L question

[dj8wl@uugate.wa7slg.ampr.org]

Hello Dave, hello Kevin, hello all,

I have been using inverted L's here for many years. They are good performers
as far as dx and "local" communication is concerned. The longer you make
the horizontal section the more horizontal polarisation you will get. When
that horizontal section is close to ground (within 1/8 wavelength) consider
the earth acting like a reflector in your hf-beam antenna meaning most of
the radiated power is going straight up! Make the vertical section as long
as possible and use the horizontal section to resonate around 1700 kHz.
Then you need a capacitor at the feedpoint (typically 200...500 pf) to
cancel the (inductive) reactance. You will end up with a feedpoint im-
pedance between 35...50 ohms. All you need is a good ground system to
keep losses down. Stew/W1BB also was recommending inverted-L's with
about 3/8 wavelength (total length) which radiate equally well at low
and high angles. The current in the antenna is responsible for the
field. Keep the maximum current somewhere between vertical and horizon-
tal sections (I mean the maximum of the antenna current). In my inverted
L the maximum is just in the corner where horizontal and vertical sections
are connected. 30...50 radials is a must to keep losses down. You don't
have to bury them, however. On-the-ground radials also work fine.
I have used phased inverted L's in the past also. Minimum height should
be not below 50...60 ft. Otherwise low angle radiation will suffer.

Regards,

Peter, DJ8WL  <dj8wl @ uugate.wa7slg.ampr.org>
(255 countries conf'd, using inverted L's !)

--
FAQ on WWW:               http://www.contesting.com/topband.html
Submissions:              topband@contesting.com
Administrative requests:  topband-REQUEST@contesting.com
Sponsored by Akorn Access, Inc & KM9P