Topband: Need advice on vertical

[Jim, KJ0M]

You wrote:

> Topbanders,
> while i successfully shunt-fed the tower at our local clubstation,
> i completely failed to do so with my own tower at home.
> It is a crank-up tower with tilt-base, maybe the sections have no good
> contact, i don't know. Plus i now replaced the Titanex Log-periodic  
> with
> a SteppIR and i don't know what the RF will do to the electronics. I
> would like to try a different approach now.
>
> The tower is abt. 18m when fully cranked up, this is close to a 1/4  
> wave
> for 80m. I am thinking of building 1 or 2 inv L's for 80m and/or  
> 160m. 3
> different ideas come to (my) mind:
>
> 1. A single wire for both bands, parallel to the tower , maybe 5/8 for
> 80m , ~ 3/8 for 160m, with a matching network at the base.
> Feels complicated, right? And i am not sure about the radiation  
> angles.
>
> 2. 2 wires , each a 1/4 wave, one  left , the other one right to the
> tower , with the horizontal sections going in opposite directions.
>
> 3. One half of a trap-dipole for 160/80, converted to the L. The trap
> can handle quite some power, too old for ebay, too young for the  
> trash can.
>
> Radials.
>
> What is the easiest way out of these ?
> Or am i wrong? Should i try none of them?
> Any advice?
>
> Martin

Hi, Martin.

I have the same sort of setup, similar to #3. I have an inverted L  
with a trap so it's good on 80 and 160 meters.

I have a 4' wooden standoff attached to the top of the tower with a  
small mountaineering pulley hanging off the end of the standoff.  
Through this, I run the end of the inverted L to be tied off at some  
point distant from the tower. The base end is attached to a mounting  
point about 30 feet from the base of the tower. After trimming the two  
sections of the inverted L for resonance ( the 80 meter portion is  
about 65 feet long and the portion above the trap is about 45 feet  
long ) I ran the tower all the way up and secured the free end of the  
L so that the antenna was pulled away from the tower at an angle. Now,  
when I run the tower all the way up, the L just feeds through the  
pulley and is fully extended at about 30 degrees. If I lower, the  
tower, the L just goes slack through the pulley and lays at the base  
of the tower. I generally leave my tower down and raise it when  
conditions are good and there is no wind, etc. With the pulley,  
everything just lays slack on the ground when not in use. I use  
copper, insulated wire rope for the inverted L. It's very flexible and  
soft and never kinks.

I have 40 radials buried around the base of the L and this was a must  
for good performance, I think. I generally can work anything I can  
hear on 80 or 160 meters. It has worked very well for me, was easy to  
construct, very inexpensive, etc and I have worked 135 countries on  
160 meters from southeastern SD. The only problem is it's not the best  
receiving antenna since it's vertical, but I live in a fairly quiet  
rural location, so it works OK for Rx, not the best, but OK.

Hope this helps, Martin.  YMMV.


73,

Jim
KJØM
.-.-.