Changing the length of the feedline will affect the behavior of the 
tuner with any antenna.

This is because by changing the length of the feedline, you are also 
moving the voltage peaks that occur along it to different locations 
along the coax. Thus, the tuner is fooled into thinking it has less of 
a mismatch to handle.

The original mismatch, of course, is still there, but the transmitter 
is happy because it is looking at the low swr on the radio side of the 
tuner.

If you have some shorter lengths of coax, try them in place of the 75 
feet. You may find that even 5 or 6 feet will be enough to accomplish 
the change. The shorter length will also reduce the loss caused by the 
high SWR between the radio and the ballun.



----- Original Message ----- 
From: "Tom Behler" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Saturday, March 16, 2013 11:14 PM
Subject: Cobra Antenna Now Up


Hi, all.

Well, I didn't get to do the 40-meter round table today, because a 
couple of
hams and I were out in our 32-degree, but at least sunny weather 
putting my
Cobra Ultralite Senior antenna up this afternoon and evening.

The antenna is about 25 feet off the ground, and is pretty much a flat 
top.

Had about 30 extra feet of ladder line, which we have coiled and 
secured off
the ground near the corner of the house.  The antenna is connected to 
the
Balun Designs balun, which sits right outside my shack window.


The antenna does seem to get out, at least on 80 meters, which is 
where I
really needed an antenna.  I made a number of contacts in the North 
American
Sprint contest on 80 meters, and those contacts ranged from Minesota 
to
North Carolina, Pennsylvania, Connecticut, and South Dakota.

But, I do have a question:

At first, the antenna did not tune on the lower part of 80 and 40 
meters,
using the auto tuner in my TS590.

However, I used an old trick that I learned from the G5RV installation 
in my
RV, and a trick that, I think Lou from the list used. .. I added about 
75
feet of coax at the transmitter end of the antenna, and then it tuned 
just
fine.

Do you think this is normal for this type of antenna?

Is there something else I should try to deal with the SWR issue on the
bottom of 40 and 80?

I don't know how much more time I'll have this week-end to work with 
the
antenna, but at least it's up in the air, and can be tweaked from 
here.

Tom Behler: KB8TYJ, Big Rapids, MI