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Re: [TowerTalk] 160-m. Inverted L Question

Subject: Re: [TowerTalk] 160-m. Inverted L Question
From: Terry Conboy <>
Date: Thu, 13 Dec 2007 10:56:30 -0800
List-post: <>
At 04:18 PM 2007-12-12, Dick-K9OM wrote:
>I've been doing research on 160-meter Inverted L's and would appreciate  your
>thoughts on the following:
>1) Some people report that the 160-m. Inverted L can be fed directly with  50
>ohm coax with good results.  Is that true?
>2) Some people feed their Inverted L's with fixed 500 or 1,000 pF
>capacitors.  What advantages does this offer, such as: lower SWR 
>at  resonance, and/or
>increased bandwidth?  (again these are "fixed" capacitors  not variable)
>3) Can you offer a good resource for the 500 or 1,000pF  capacitors that will
>handle a Kw?
>I realize a variable capacitor is best as you can move around the band
>better... but for this temporary 160-m. Inverted L... I'd prefer 
>Options 1 or 2

Another approach, that gives a 50 ohm match without capacitors or 
transformers, is to use an inverted-L that is about 3.5 feet shorter 
than resonance and place a shunt coil (about 4.7 uH) across the 
feedpoint.  This forms a virtual L-network to step up the naturally 
low impedance of an inverted-L.  I use this approach with a four-leg 
inverted-L with a very short vertical section.  The loss in the 
matching coil is well under 0.1 dB.

Using the shunt coil match (also known as beta or hairpin match) 
actually gives a very slightly wider SWR bandwidth than the 
series-cap matching approach.  In addition, the shorter horizontal 
wire of the shunt-matched inverted-L decreases the high angle 
radiation.  Of course, if you're mostly interested in short-haul 
contacts, the longer wire needed with the series-C match would be an advantage.

The gain at low angles is very similar regardless of the matching 
approach used.  The ground losses are indeed lower with the series-C 
approach, due to the higher feed Z, but all of the extra signal takes 
off at high angles.  I'll forward to Dick another message containing 
patterns and SWR numbers comparing series matched, resonant, and 
shunt matched inverted-L's that I ran recently.

73, Terry N6RY


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