[TowerTalk] Can take-off angle be too low?
alsopb
alsopb@gloryroad.net
Mon, 11 Dec 2000 11:49:39 +0000
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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