Topband: Inverted-L

[George (K8GG) & Marijke Guerin]

Topbanders,

Here is my two cents worth:

>
>> W8JI wrote:
>> > I'd never make the L 3/8th wave.
>>
>> > I'd make the inverted L a 1/4 wl.

If one uses a 1/4 wl inverted-L, then it can be easly matched by an UnUn. 
Examples can be found at:
http://www.amidoncorp.com/aai_cost_ununs.htm
The UnUn labeled:
W2FMI-1.78:1-HMMU50 (multi-match UNUN)
has lots of input and output taps and can match impedances from 3.13 up to 
37 ohms.
Keeping the 160 meter inverted-L connected to ground through the windings 
prevents it from being a resonant half wave floating wire on 80 when using 
the 80 meter vertical nearby.

Tom G3OLB wrote:

> The advantage with making it a little longer than 1/4 wl is that it tunes
> with a simple series C. What's your recommended way of matching a true 1/4
> wl to 50 ohm coax?
>
The problem here is that to get to about 50 ohms (tuning out the inductive 
reactance with a vacuum capacitor of 400 - 450 pfd), one needs a 5/16 wl 
inverted-L (160 ft length) 80+ feet up and 80- feet out over 3000+ feet of 
radials to get a good ground.  It works great if you have the space, time 
and energy to do it right.  Going to a lower 3/8 wl configuration makes for 
lots of horizontally polarized radiation from the about 1/4 wl horizontal 
part of the wire and over 1/2 the energy goes nearly straight up... not good 
in my opinion.

GL  73        George    K8GG
...snip...