Topband: Inverted L SWR Jumps ???

[Tim Duffy K3LR]

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 at contesting.com] On Behalf Of Ashton
Lee
Sent: Tuesday, November 27, 2012 11:49 PM
To: topband at 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
_______________________________________________
Topband reflector - topband at contesting.com