Topband: Inverted L question

[Guy Olinger K2AV]

On Wed, Dec 26, 2012 at 3:08 PM, Tom W8JI <w8ji at w8ji.com> wrote:

>
> At any distance less than 1/4 wave or so, which is around 130 feet, the
> inverted L is coupled very tightly to the tower. At wider spacings, like
> 50-100 feet, the tower and things on the tower **sometimes** won't have
> much interaction. Of course if you are unlucky, interaction can be severe
> even at a hundred feet spacing or more.
> [Several more paragraphs of good stuff.]


Completely agree with Tom.

Tom didn't elaborate on just how BAD that loss can be.  Think of your L and
your tower as being two windings on the same transformer.  If the base of
your tower is just in the ground, and directly tower connected steel guys
go to steel anchors in the ground, that basically is a close-coupled
transformer winding connected to a big resistor.

Some have moved the feed, supporting the far end of the L horizontal with
the tower, and using a tree to support the bend in the L.

If your tower is the only possible support and you can't relocate the L,
 you will have to prep the tower just the same as if you were going to feed
it with a gamma match.  Among all the other stuff, the L feed and the tower
base must share the radial field.  If you have to do all the work to prep
the tower, maybe forget the L and just load the tower.  Lot of loud
stations out there loading  up their tower over a quality radial system.

Even if you keep the feed at the tower, don't skimp on the radials.  Do
them right.  Take the time.  The radials/counterpoise is always the most
important performance detail.  Nothing in second place.

73, Guy