Topband: matching an inverted-L

Wes Attaway (N5WA)
Tue, 03 Dec 2002 06:09:50 -0500

>From your earlier e-mail I am not clear as to the total length of
your Inverted-L.  You said 70' ..... is this total length
(vertical + horizontal), or just the vertical portion?  If the
total length is 70' then you will indeed need some additional
matching somewhere in the system if your TX tuner won't handle
the problem.

On the other hand, a full size L (135' or so total length) should
not need any tuner for a reasonable match to 50-ohms.  The
easiest way to tune one is to just vary the horizontal length a
bit to get the lowest SWR at the point you want it.  Unless
something is very wrong, or you want extreme bandwidth, you
should be able to stay within reasonable limits of SWR without
any additional matching components.  By reasonable limits, I mean
something that can be easily handled by your transmitter's output
matching circuit.

As long as your transmitter can "match" the load you will not
gain anything by adding stuff out at the antenna just to present
a nice impedance to the output side of the transmitter's matching
circuit.  In his book "Reflections", Maxwell fully explained why
it really makes no difference where the "matching" takes place.
It can be anywhere along the line, or even at several places
along the line.  Having a perfect match out at the antenna does
more to make hams feel good than anything else.