[TowerTalk] Re: Can takeoff angle be too low?
n4kg@juno.com
n4kg@juno.com
Mon, 18 Dec 2000 23:41:42 -0600
N4KG responses inserted following appropriate paragraphs.
Previous discussion omitted for brevity.
On Mon, 18 Dec 2000 Pete Smith <n4zr@contesting.com> writes:
> Wait a second....
>
> N6BV's original data made certain assumptions about the antenna on
> either end of the path. In about October 98, he revised the data,
based
> on assuming isotropic antennas at each end of the path. These tended
> in general to give more weight to lower-angle modes. (N4ZR)
As one would expect. A more complete understanding
would be obtained by calculating the path loss for each
mode (waveangle) supported by the ionopshere and then
applying the energy radiated at the various angles by
antennas of different heights from the minimum to
maximum height typical of amateur installations.
It is a LOT of work, but would be a more accurate
representation of amateur signals. de N4KG
> In both cases, my understanding is that only the best mode
> was counted, even in cases where there were 4 or 5 different ones,
> some within a few dB of the best one. (N4ZR)
>
Which leads to the mis-assumptions so prevalent today,
that higher angles DO NOT PROPAGATE, EVER,
since the data was misrepresented by omission.
de N4KG
> If you assume low dipoles and/or tribanders on the other end of a
> W1-4/EU path, then a high antenna may have a null right where the
> European antenna is concentrating its energy. There will be times
> when (with these antennas) signal strength will be significantly better
> at a higher angle (with more hops) than at a lower one. The result
> could very well be a perceived (and real) advantage to the lower
> antenna at those times. (N4ZR)
As has been reported by MANY observers but
dismissed by interpreters of incomplete or
inaccurate computer models, many of whom
have not made their own OBSERVATIONS.
de N4KG
(Note that HF Broadcast stations in Europe
are NOT representative of the typical DX
station with low antennas that we are trying
to hear in contests.) de N4KG
>
> Try to apply the same principle in W9 or W5 and it probably doesn't
> prove out, because those high angle modes are not present for much
> of the time, and when they are the signal level is less. (N4ZR)
>
Ah, N2IC/0 and WE9V, among others, have reported
Low antennas beating out stacks during mid day.
Even KL7Y or KL7RA (I forgot which) has reported
their LOW 10M antenna was BEST at certain times.
de N4KG
> Because their vertical lobes are wider, stacks probably average
> better than a single Yagi, more of the time. (N4ZR)
A LOW antenna has a wider vertical lobe than stacks.
Stacks have a wider lobe than the high antenna alone.
Is the pattern of a pair of 8.5 dBi stacks any wider
than a single 10.5 dBi antenna at the average height
of the stack? I suspect not. de N4KG
As an antenna is raised, each single degree that the
low side of the lobe is lowered, the upper side of the
lobe is lowered by THREE degrees, narrowing the lobes.
de N4KG
>
> What am I saying? Everyone is right, depending on his situation.
> There is no one right answer. There's no substitute for individual
> analysis, taking your terrain and propagation into consideration.
> (N4ZR)
AMEN !
As has been said MANY times by MANY reporters
(with MANY antennas) :
You can NEVER have TOO MANY antennas !
Because of the NULLS in the vertical pattern of
Horizontally Polarized Antennas, it is IMPOSSIBLE
for any SINGLE Antenna to cover ALL the angles
that are supported by the ionosphere in spite of
the never ending desire to find the OPTIMUM height
for one single antenna! de N4KG
TWO antennas positioned such that the Low antenna
fills in the first NULL of the High antenna is a BIG
improvement over a single antenna at any height.
Simple translation: NO SINGLE ANTENNA can cover
ALL the angles supported by the ionosphere. de N4KG
The land limited amateurs don't want to hear this
and keep the dream of finding an "optimum" height
alive.
SO, how about all you guys with Stack Matches
and 4 high stacks ( or even 2 high stacks) making
some observations and reporting your findings?
Please include data on your foreground / terrain,
time of year, and sunspot data. Note that the
antenna with the LEAST received signal is often
the BEST indicator of arrival angle due to the
narrow range of deep NULLS.
de Tom N4KG
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