Re: Inverted-L (was OT: Vertical antenna)

Posted by Edward R Cole on Dec 21, 2010; 7:06pm
URL: http://elecraft.85.s1.nabble.com/Inverted-L-was-OT-Vertical-antenna-tp5852957p5857590.html

Observational note on radials on the ground.  My 43x130 foot
inverted-L requires more inductance in the summer for resonance.  I
see the change about a month after ground freeze-up (but that may
vary with moisture content of the ground).  Fall usually exhibits
saturated ground due to the rainy season, whereas spring is typically
dry after the thaw (May is our sunniest month).

My 50-70 foot chicken wire radials are short for 500-KHz but do have
a higher velocity factor (not measured).  I do not have property for
930-foot radials!  More metal under the inverted-L would be better
but this is my practical limit.  I have not spent much time looking
at 160m and 80m tuning of the antenna, but will, eventually.  The
original design was for a 80m half-square but comparison with the
inverted-L does not make it desirable enough for the complication in
design.  The antenna hears well (Buffalo, NY on 511-KHz from
Alaska).  I will begin my winter beacon transmissions later this week
(WSPR on 501-KHz, 4.15w ERP).

The use of a 120-foot radial (shield of my VHF Heliax cable) makes
the inverted-L near to a tuned counterpoise on 80m with the elevated
130-foot top wire of the inverted-L (in fact the top is too long when
you add the 43-foot vertical wire).  I'm sure there will be some
interesting impedances with this antenna as frequency is
moved.  Fortunately, the base coil can be adjusted using taps to find
resonance.  Impedance match is a separate issue.

Before adding a base coil I could load the inverted-L on 80m using an
antenna tuner at the radio.  But this would have high SWR on the coax
with additional loss.  On 500-KHz I have Z = 53 +j0 on the coax by
tapping above the grounded end of the base coil.


73, Ed - KL7UW, WD2XSH/45
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