You raise some good points for large station design Tom,
but the original topic was filling in the NULLS for a SINGLE
(moderately) high antenna, presumably a tribander.
I'm merely suggesting that for tower heights of 60 ft or more,
that adding a lower antenna 20 to 30 ft below, will improve
coverage of the intermediate waveangles by filling in the NULLS
without "cluttering" the tower.
Your point about trying to avoid shooting through other
antennas (or ANY metalic objects / conductors) is valid
One of my 5L10's was fixed on Europe at 40 ft pointing
over my house. It was my WORST antenna to EU on 10M,
UNTIL I moved it to another tower that had a clear shot
where it became my BEST 10M antenna to EU.
The path from the original site was aimed directly at
an 18 ft long piece of flashing at 18 ft on the house,
about 80? ft from the tower. I assume that piece of
metal was acting as a 10M reflector, directly in the
path of the ground reflection, costing me the 6 dB
ground reflection gain.
Returning to the original topic:
There seems to be a STRONG reluctance among users
of BIG and HIGH antennas to ever believe that a (smaller)
and especially a LOWER antenna will ever be stronger
when working DX. All I can say is if you have never seen
it (i.e. you don't have a low antenna for comparison), you
tend not to believe it.
I received two testimonials from people with 180 and 200 ft
high switchable stacks who BOTH reported they switched to a
single LOW antenna (35 and 45 ft) during parts of the day because
that was the BEST antenna at the time for EUROPE and AFRICA,
especially on 10 and 15M.
I have asked each to copy their notes to TowerTalk.
One of them only had antennas above 100 ft until he
noticed he was struggling to EU and AF during the day.
When he discovered a single C3 at 30 ft was stomping
his BIG HIGH antennas, he added some more antennas
to his stack at 35 and 70 ft.
My friends who have installed LOW antennas ALL
report there are times that they are indeed better
than their higher antennas to EU and AF
and even to JA during high sunspot levels.
My TH7 at 40 ft is a GIANT KILLER to Africa on 20 and 15M.
I never have to turn the 20 and 15M monobanders to bust the
HUGE afternoon pileups on African DX. I confess my 5L10
is significantly better than the TH7 on 10M but I suspect that
may be a tuning problem since the TH7 was designed to cover
all the way to 29.7 MHz.
One other point about high antennas. At 110 to 120 ft, there
is a significant (but more narrow) second lobe that falls in the
center of the high angle range of a 40 ft high antenna on
ALL of the high bands (from 10M through 20M) so
many of the high antenna proponents may actually be
using a high angle path without realizing it. Again, a lower
antenna is still needed to fill in the intermediate NULLS.
For the remaining skeptics,
I suggest you TRY IT for yourself
and let us know what *you* observe.
On Fri, 11 Jan 2002 "Tom Rauch" <email@example.com> writes:
> > > Very often, the real point behind such kind of questions is
> > > *where do I place the only antenna I can have, to get
> > > the best results in this conditions ?*.
> > >
> > SNIP
> > > 73,
> > > Mauri I4JMY
> > >
> > For a tower of 60 ft or more, it is trivial to add
> > a trap dipole or small (2L) tribander at 30 to 40 ft
> > to fill in the unavoidable 10 to 50 dB NULLS
> > in the vertical plane pattern of a higher Yagi.
> While it is nice to have an antenna that compliments the nulls of
> another antenna with a nice lobe, there are other worries.
> All my life I have used high yagi's, and never have noticed a
> problem. While I might not be slamming an S meter at 500 miles,
> I'm still almost always first or second through and often beat
> stacks of yagis with my single antennas. I've really never heard
> anything that I can't work quickly, unless they just aren't working
> anyone around my general area of the USA.
> I tend to use heights like Pete suggested, up around 100 feet.
> My six meter antenna is a pair of 5 element yagis stacked 20 feet
> or so apart with a mean height of 140 or 150 feet.
> I've found it is much more important NOT to clutter up the tower
> with 10 or 20 antennas, or have 3 or 4 towers within 300 feet of
> each other where the higher frequency antennas aim through the
> lower frequency antennas, than it is to pick a sweet height.
> The worse performing stations I recall are those with too many
> antenna jammed in a small area.
> In hundreds of AB tests on 160 meters, I've found even on 160 a
> high wave angle is useless for anything over a few hundred miles.
> They only time high angle antennas work at all is when the signals
> are so strong no one needs to worry about signal level.
> I think it is valid to worry a bit about filling in low angle nulls,
> but I'd be far more concerned with too much junk around the
> antenna or in front of the antenna.
> 73, Tom W8JI
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