W8JI added:
> > Excellent points, gentlemen. Even with a current
>balun/choke at the
> > feedpoint, the coax feedline can easily couple to the
>antenna & radials and
> > skew the pattern.
>
>It doesn't just skew the pattern, it brings RF into the
>shack and also reduces system efficiency by making lossy
>earth part of the antenna system.
>
>Small radial systems require careful installation as well as
>careful feedline decoupling.
I can confirm that.
For the first time ever, I have an elevated HF2 some distance
away from the shack (as in not within three meters of operating
position - more like a quarter-wave at 80m [palacial for VR2]).
I still see patterns in the computer monitor when I transmit
(400 watts) on 80m.
There is not enough spare coax after going all the way out there
in order to coil some up to choke the feeder.
And even if I did have enough, the routing of the feeder is
certain to problematic. At a previous QTH with proximity &
proper decoupling, there was less of a problem than now.
When I have a tribander with a smaller wing span, the HF2 goes
back on the roof - maybe if I were so lucky to live in the middle of
nowhere then ground mounting may be okay - but even in rural HK,
ground clutter is certain to muck up any GP that isn't elevated at
least 10m).
73, VR2BrettGraham
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|