Re: Topband: Inverted L SWR Jumps ???

["ZR" <zr@jeremy.mv.com>]

Ive often wondered about actual coupling Tim as compared to modeling.
For decades Ive had an inverted vee midway between a pair of full size 
sloping verticals all on the same tower. The vee feedpoint is about 20' from 
the tops of the verticals which show excellent directivity and performance. 
The vee also has its own independent response and shows no VSWR changes when 
switching directions with the verticals.
Im just assuming (which usually gets me into trouble) that the low angle 
vertically polarized RF from the 10' above ground feed of the verticals and 
the high angle horizontal radiation of the vee are pretty well isolated. 
There has never been any arcing back at the house using a simple B&W switch 
which is just a ceramic wafer with unused positions floating.
Carl
KM1H



> Hello Ashton,
>
> I am curious what "pretty well separated" is at your QTH? Two 160 meter
> antennas separated by 240 feet is the same as having two 2 meter antennas 
> 38
> inches apart.
>
> There is significant coupling between 160 meter antennas that are 
> separated
> by as much as 500 feet and this coupling could be problem for your set up.
>
> 73,
> Tim K3LR
>
> -----Original Message-----
> From: Topband [mailto:topband-bounces@contesting.com] On Behalf Of Ashton
> Lee
> Sent: Tuesday, November 27, 2012 11:49 PM
> To: topband@contesting.com
> Subject: Topband: Inverted L SWR Jumps ???
>
> So I am trying to get set up better on 160 meters. I now have two antennas
> up (pretty well separated). One is an Alpha Delta DX A sloper hung in a 
> tree
> with a grounding wire led to a ground rod and small radial field. The 
> other
> is an inverted L on a good radial system of about 2000 feet in various
> lengths of about 50 feet each as fit the yard. Both are resonant at about
> 1.830 .
>
> The sloper loads fine all the way up to 1500 watts. The inverted L loads
> just fine to about 700 watts and then causes the Alpha amp to fault out. I
> think I am getting a sudden change in antenna impedance. The antenna is 
> fed
> through a 5 KW rated choke balun. The feed line exits the base between
> radials. I've tried various feed line lengths, I've replaced every 
> component
> in the system except for the antenna wire. The antenna does climb along 
> the
> branches of a tall pine before L-ing outward at about 55 feet. I think the
> problem is worse at night time when things are cold (and perhaps more
> humid).
>
> What I see on the amp is output power suddenly seem to surge to 2500 
> watts,
> and reflected power jump from a few watts to over what the amp can read.
> then in a flash the amp faults out. This all happens with only about 20
> watts of drive, so the amp can't actually be putting out 2500 watts unless
> something very strange has happened. As I noted, using the other antenna 
> all
> is good.
>
> I need to get the inverted L working since it seems to have substantial
> receive gain vs the sloper, so I assume it will be equally better on
> transmit.
>
> All advice is welcome. Am I likely to be "arc-ing" to the tree branches?
> Could the wire be the problem? Do inverted L's have trouble with full 
> power?
> The same wire worked fine for the last few years, but fed against a much
> lesser radial field and run through a less dense, lower tree.
>
> I'll be trying everything I can think of tomorrow afternoon, starting by
> trying to minimize contact with the tree branches. All suggestions 
> welcome.
> 73
> KQ0C
> Ash
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