Andiroo wrote in news:1189004672.355388.8520
@k79g2000hse.googlegroups.com:

....
All

More on the nature of the problem. I have basically fitted a 1/2 size
G5RV. Its fitted at 30 ft high between a pole at the end of the yard
and the chimney at approx 30 ft high. The ladder line falls pretty
much vertically except for the very end where i have had to divert it
away from a steel cast iron style balcony which surrounds a roof
terrace on the first floor. I figured it would not be good to brush
alongside the balcony as its metal.

Anyway, i am getting some very weird SWR readings even when i am using
my automatic ATU (LDG Z-100. These range from close to 1.1:1 on
40metres all the way up to 3.1: 1 in the middle of the 20 metre band.
I am trying to work out where the problem may lie. So far i have come
up wiith:
....

You might find my article on optimising the G5RV of interest. You will
need to scale for a half size G5RV, so scale the frequency axis of the
graph times two, and when it tells you to check for an electrical half
wave of open wire line at 14Mhz, you need to do it at 28Mhz etc. The
article is at http://www.vk1od.net/G5RV/optimising.htm .

After some basic DC tests for proper and reliable connection, no short
circuits etc, next is some more serious RF evaluation of the antenna
system.

The commonest reason for a G5RV to perform worse than expected is that
the open wire line is an incorrect length, usually due to not properly
considering its velocity factor. (If you purchased a kit, as so many
people seem to do nowadays, you would hope that the supplier got this
correct... but?) Next is the length of the dipole which is often
regarded as not affected by its environment. (This applies to a
commercial kit as well as a DIY G5RV.) A tape measure is the start of
setting up a G5RV, not the end.

Owen