[TowerTalk] Re: [TowerTalk] Can take-off angle be too low? Comme
nt de KØFF
K0FF
K0FF@ARRL.NET
Mon, 11 Dec 2000 07:30:49 -0600
Sorry I haven't had time to follow this thread very closely, but would like
to
add that 10M as well as 6M enjoys Es skip seasonally as well as F skip,
and the arrival angles are very different. On 6M especially it is evident in
the
summer when Es signals, even from EU are better on lower ( or "tuned
against ground")
antennas, VS just brute height. My experiments have shown reliable results
tracking
F VS Es and it is quite pronounced. On 10M, the situation is similar, but of
course
there is a great deal more F2 to enjoy.
One thing for sure is that there is no one antenna perfect for every type of
propagation
situation. However very good compromise heights have been worked out, and of
course the
best answer is to have either separate towers, or at least stacked antennas
at different
heights to take advantage of different skip conditions.
Other modes are available on 6M as well, including tropo, Meteor Scatter and
Aurora, and each
of these adds to the complexity of choosing but a single antenna.
Suffice to say, that in terms of wavelength, higher is not always better.
For my 6M experiments, I use an 11 el at 105', a 7 el on a 60- ft motorized
tower,
and 4 x 6 el on a 72' motorized tower, also with full elevation.
For a real kick try even a short 10M beam on an elevation
mount....surprising
to see from what part of the sky the signal is really coming from.
Depending upon the exact band conditions, each of these antennas is far
superior
than the others. This same effect is very evident on 20M due to the arrival
angles during the
daytime being higher than at night ( over the pole long haul). An antenna
setup designed
to be most effective from the US Midwest to VU for example
( say stacked monobanders at 1 and 2 WL) may very well be trounced into the
Caribbean by a
tribander at 50 feet, on occasion. Come the long haul though, the tribander
is deaf.
If a single antenna is all that can be accomplished, on 6M the best
compromise height works
out to be just short of 3 wavelengths (abt 55 feet.). This height gives
good lobes at the low angles required for F, and also another major lobe at
12+ degrees required for Es. Scaled up for 10 meters(10.5 meters actually =
28.5 MHz), that would be around 100 feet.
I'm afraid that many on-air comparisons may be skewed by interactions with
other
antennas on the same tower, or on other towers spaced too closely. My towers
are
space out 250 feet apart for this reason.
Nothing here contradicts data supplied by others. The datum are correct,
it's just that the scenario changes so drastically on theses higher bands.
Happy Building, Geo>KØFF
http://homepages.dstream.net/K0FF
----- Original Message -----
From: alsopb <alsopb@gloryroad.net>
To: <n4kg@juno.com>; <towertalk@contesting.com>
Sent: Monday, December 11, 2000 5:49 AM
Subject: Re: [TowerTalk] Can take-off angle be too low?
> Guys,
>
> I don't understand. The first lobe for an 80' high antenna on 10M is
> in the range of 7 degrees. The histogram data for arriving angles
> (from YT East coast to EU) shows the peak of the distribution at 8
> degrees. It extends to 2 degrees on the lower side and 12 degrees on
> the upper side. There are a few outlier points (perhaps 5% of the
> population) above 12 degrees. The 60-80' high yagi spans this
> distribution almost exactly. Lower antennas miss quite a bit of the
> lower angle stuff.
>
> I've often heard the "magic" of lower antennas on 10M but this type of
> data seems to contradict it.
>
> I believe the above histogram data is averaged over the entire sunspot
> cycle and time of year. Calcs I've done with VOACAP indicate that if
> anything lower angles occur more frequently during high solar flux
> levels. Lower antennas should be even worse. The variation of angle
> with the opening indicates that there may be a small period of time
> when higher angles predominate, but this is very dependent of solar
> flux levels and time of year. The betting man wouldn't count on it.
>
> It appears that "experience" and calculation are at odds.
>
> One thing I do agree with is that something is wrong with an 80'
> antenna which never produces a better signal than a lower one.
>
> 73 de Brian/K3KO
>
> n4kg@juno.com wrote:
> >
> > Now that I think about it, there is a time when the TH6
> > at 80 ft is better than the lower Triband antennas (but
> > not the 5L10 at 60 ft...that antenna is a KILLER).
> >
> > In the late afternoon / early evening, South America
> > and the Caribbean is often better on the HIGH tribander.
> >
> > I attribute that to two conditions:
> >
> > First, the MUF is falling so the high angles favored
> > by the low antennas may no longer be supported,
> >
> > Second, from W4, the Caribbean, Central America,
> > and the North Coast of South America are within
> > one skip range at very LOW angles favored by
> > higher antennas.
> >
> > For Europe and Africa, my 35 to 60 ft high antennas
> > are always better than the 80 ft high TH6 on 10M.
> >
> > (Those 5L monobanders have 10.5 dBi free space
> > gain by my model. I would be surprised if the TH6 is
> > over 7.5 dBi. My model shows that the 15M director
> > on the TH6 reduces 10M gain by 1 dB.)
> >
> > That 80 ft tower is heavily rusted and needs to come
> > down. I will check all the traps at that time on that
> > old antenna. When I refurbished my TH3, I found
> > a couple of loose coil screws and a loose trap cover
> > screw.
> >
> > OTOH,
> > >From my previous QTH in town, my TH3 at 50 ft was
> > a killer on 10M, usually better than a 2L Quad at 80 ft.
> > to EU, AF, and SA (overlooking a 3 degree down slope).
> >
> > >From K4GSU (now N4AR) we found that a CC 4L15 at
> > 50 ft was a much better multiplier pileup buster than a
> > 6L15 at 90 ft during the day to EU / AF.
> >
> > IMHO, antennas at 80 to 100 ft are much better performers
> > after dark, from 10 through 40 meters.
> >
> > de Tom N4KG
> >
> > >>>>>>>>>>>>
> >
> > On Sun, 10 Dec 2000 22:58:44 -0500 "Guy Olinger, K2AV"
> > <k2av@contesting.com> writes:
> > > The story you tell is too one-sided. Check 80' antenna, feedline...
> > > particularly feedline if your SWR is wonderfully low all across the
> > > bands.
> > >
> > > -----------------
> > >
> > > Guy Olinger
> > > Apex, NC, USA
> > >
> > > ----- Original Message -----
> > > From: <n4kg@juno.com>
> > > To: <TOWERTALK@contesting.com>; <cdietz@swbell.net>
> > > Sent: Sunday, December 10, 2000 12:43 PM
> > > Subject: Re: [TowerTalk] Can take-off angle be too low?
> > >
> > >
> > > > Here we go again.
> > > >
> > > > I find that my TH6 at 80 ft is the absolute WORST
> > > > performer of all my antennas on 10M, including
> > > > a TH7 at 40, TH3 at 40 ft fixed SE, 5L10 at 60 ft,
> > > > and 5L10 at 35 ft fixed on EU.
> > > >
> > > > The 80 ft high TH6 is NEVER better than any
> > > > of the other (lower) antennas on 10M.
> > > >
> > > > On 15 and 20M, the TH6 at 80 ft sometimes is
> > > > a good band opener and closer but is usually
> > > > not as good at the TH7 at 40 ft or 4L15 at 55 ft
> > > > when the band has opened up.
> > > >
> > > > During midday, the 40 ft TH7 is often the best
> > > > antenna on 20M and still not a bad performer
> > > > at night. I never bother to move a higher antenna
> > > > to Africa where the low TH7 works all.
> > > >
> > > > For domentic contests, an 80 ft high antenna
> > > > has a null at 600 to 1000 miles on 20M. My TH7
> > > > at ft 40 is typically 20 to 40 dB stronder into
> > > > W1, 2, 0 than the 80 ft high TH6.
> > > >
> > > > de Tom N4KG in North Central Alabama
> > > >
> > > > (300 miles south of Indianapolis,
> > > > 20 miles south of Tennessee,
> > > > 60 miles east of Mississippi)
> > > >
> > > > ////////////////////////////////////////////
> > > >
> > > > On Sat, 04 Nov 2000 Logan <cdietz@swbell.net> writes:
> > > > >
> > > > > > On Thu, 29 Jun 2000 "Tonno Vahk" <tonno.vahk@hansa.ee>
> > > writes:
> > > > > > >
> > > > > > >
> > > > > > > How important is it to have the ability of running very low
> > > > > > > elevation angles in upper HF contesting?
> > > > >
> > > > > The prevailing wisdom is high antennas open and close the
> > > band...Low
> > > > > antennas when it is wide open.
> > > > >
> > > > > In Texas for the path to Europe if one only could have one
> > > antenna,
> > > > > 75
> > > > > feet would be best on 10-15-20 meters. I understand this height
> > > is
> > > > > about 55 feet on the East Coast of the US.
> > > > >
> > > > > I do a lot of contesting on 10 meters and 75 feet is certainly
> > > the
> > > > > "bread and butter" (best overall) height to Europe from here.
> > > From
> > > > > this
> > > > > statistic, and since Texas is the center of the World...Well,
> > > about
> > > > > the
> > > > > center of the US for Europeans...I would think 75 feet would be
> > > the
> > > > > best
> > > > > height for a single antenna for working the most US stations in
> > > a
> > > > > contest.
> > > > >
> > > > > That's my story and I'm stickin too it!
> > > > >
> > > > > Chuck, W5PR
> > > > > ex: KZ5MM
> > > >
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