> Under-performing stations aren't the stations on small lots. They
> are the stations who try to stick too many antennas in a small
> area, or that rely on magic like asymmetrical feeds and "lossless
> loading" schemes and think that three or four radials .05wl above
> ground or less somehow does the trick.
> 73, Tom W8JI
> W8JI@contesting.com
Knowing that a small environment doesn't lead to anything magic, a clean
idea that minimizes interactions between a forest of different radiators for
lower bands is absolutely the most correct approach in my opinion.
This is what I did with an almost square space of 45x45 ft. on a flat
concrete rooftop, at 60 ft from ground (the shack located 3 ft below roof)
to have a single structure and 5 (6) bands.
A decided for installing a guyed (nylon) 30 ft high tower in the middle of
the square space, with a 20/15/10 m multiband yagi and a rotator on the top.
Before of installing I grounded all the yagi elements to it's boom in order
to avoid arcings and maximize loading when useing as a top hat on 40 and 80.
To be sucessful in matching with a simple gamma (the capacitors at base
inside a single fiberglass box where shunt wires come in) two shunt feeds
and separate lines for 80 and 40m were added. Finally the 80m tap went
close to the top of the tower and that for 40m about 20 ft. high from base.
The available roof had been *covered* by 36 radials, as much as I decided to
go over the number 16 what could have been enough since less than 1/4 wl
long on 40 and less than 1/8 Wl on 80.
Later I also discovered that simply omega matching the 80m gamma with anoter
vacuum cap. (abt. 430 pF) the 80m structure was matched and tuned 1.830,
although the 2:1 BW was quite narrow, less than 20 KHz.
Unless with a yagi on 40 if one has rotator and tower strong enough, and the
room for the antenna and mainly his roof is at least > 1/8 Wl high from
actual ground, I don't think any other compact antenna of that height could
have been a much better compromise for an high and low bands setup in a
square of only 45x45 ft.
73,
Mauri I4JMY
PS:
To enhance reception, a tunable (7-1.8 Mhz) and rotable loop made with 2"
aluminium tubing and 7 ft diameter was placed on a roof corner. When
resonated, the loop was so coupled to the vertical structure (expecially on
80 and 160) that the only practical good heading was that to set the loop
notch (quite narrow) exactly toward the vertical structure.
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