Ken Bessler wrote:

"Ken Bessler" wrote in message news:...


My current antenna is a modified Van Gordon "All Bander".
For reference, the stock antenna is 134' of 14g stranded
bare copper fed with 100' of 450 ohm ladder line. I cut off
half of the ladder line and replaced it with a 12 turn, 5-1/4"
rg58 coil. 20 feet of rg58 goes from the coil into the shack.
I then trimmed the antenna to 7.175 mhz.

The antenna is a flat dipole up 20'. Seems to work OK but
I've got the itch to improve it. The feed point is 12" above
the peak of my roof. I was thinking about installing a 5' tripod
and 2 ten foot masts to elevate the antenna's feed point and
convert it into an inverted V. There will be no need to add to
the feedline.



snip


Well, it's up guys! The apex is about 40' and the ends are 28'.
Comparing it to my other antennas I'm seeing about a 1-1/2 to
2 S unit improvement on 40m and more on the higher bands.

I did a SWR plot before and after changing it and here's the
sticking point: Before, I had a 2:1 range from 6.900-7.280 and
now I've got 7.000-7.300 but the minimum SWR went from
1.10:1 to 1.55:1. My Elecraft KAT2 autotuner handles that very
easily but I'm wondering what would happen if I added 12 feet
to my 50' of 450 ohm ladder line? Would the minimum SWR
get better or just move? Or both? Does it really matter? (I don't
think it matters based on what I've read here).

Ken

SWR has nothing to do with the length of line [assuming low loss line].
SWR is determined solely by the antenna to transmission line impedance.
[e.g. an antenna input impedance of 70 ohms and a 50 ohm cable has a SWR
of 1.4:1 ALL the time].

SWR changes as a function of antenna height above ground because of
ground effects. Don't worry about it! The ground effect has a mutual
impedance impact on the antenna. Antennas close to ground, 1/4
wavelength, tend to have lower feedpoint impedances. Antennas 1/4
wavelength high will exhibit a higher impedance that will oscillate and
converge on Ro as a function of higher height, ultimately achieving Ro
in free space.

It doesn't matter in the amateur radio world or the engineering world.
Physicists will want to understand all the variables involved in the
interest of science. That's great! But, I'm more into amateur radio and
not physics.