[Towertalk] Re: [Force 12 Talk] XR dilemma

[n4kg@juno.com]

On Mon, 24 Jun 2002 10:20:24 -0400 "Guy Olinger, K2AV"
<k2av@contesting.com> writes:
> The original post was about using a C31XR on EIGHTEEN POINT ONE MHz.
> That's a band it was not designed for. And that a low dipole would
> beat it.
> 
> Where did you get **TEN** meters from? Stick to the subject.

My TEN Meter note was in response to a private note from another
reader who was asking about very low 10M antennas (at 20 ft).
I did not want to publicly post his comments without permission
but I thought my response might be of interest to others so I
posted it (without inclusion of the original 10M comments).

My computer crashed and apparently multiple copies got
sent out under the original XR dilemma heading without my
knowledge.  I resent the same text under the title '10M Takeoff 
Angles'.  Sorry if that confused anyone.   N4KG

> 
> Propagation on 18 is a lot most like TWENTY meters, anyway.
> 
> And will anyone mention that this angle business is a very sparsely
> supported "science" with a lot of unanswered questions and modes, 
> and lots of unexplained contrary anecdotal material.

N6BV has made EXTENSIVE studies of takeoff angles from NA
to the rest of the world on ALL BANDS using Ioncap models.
His original work was published by ARRL in the Handbook
(and / or Antenna Handbook).  He *assumed* 60 ft high antennas
for 10 through 15M and 100 ft high antennas for 17 through 80M
in his original work.  He later revised these studies using isotropic
sources to avoild the pattern nulls of the antennas at fixed heights.
This data is available on the ARRL Web Site and on CD in the
latest ARRL ANTENNA HANDBOOK.   I 'believe' the
highest angle supported by the ionosphere at 18 MHz to be 
around 30+ degrees, assuming an MUF of 50 MHz.  I have
other privately supplied data which also supports this conclusion.
de N4KG

A simplistic approach to determining the maximum waveangle
that is supported by the ionosphere is to merely *observe* the
closest stations heard on a given band and look up the SKIP
distance vs. TAKEOFF Angle in any ARRL Antenna Book.
Of course, it is necessary to distinguish between F2 propagation
and E Layer propagation.  de N4KG

> Used a 15 foot high fifteen meter dipole as a teenage Novice 
> operator
> in Kentucky. Since nobody had tried to tell me that all that energy
> would go straight into outer space, I went ahead and worked a couple
> thousand contacts on it, more USA than not. I got lots of 599/589
> reports running a mere 50 watts, at a time where you had to get the
> QSL address over the air because you couldn't afford a call book, 
> and the automatic 599 hadn't been invented yet.
> 
> I worked all the surrounding states on 15 meters. This on a 
> frequency higher than in the original post. How does one do that if
those 
> angle formulas are really absolute and trustworthy?
> 
> ***!!!>>> Or is it really that the angle formulas describe a rather
> broad and fuzzy center of probability, with a lot contrary evidence
> suggesting that there is something yet to be discovered?
> 
> 18 MHz dipole at 20 feet will work. Easy experiment. Try it. See how
> many Europeans you work and get 5NN as a report.
> 
> 73, Guy.

My guess is that your Teenage experiences were in the mid 1950's,
when we enjoyed the highest sunspot activity of the last 50 years.

I'm not saying that a very low antenna won't radiate any energy
that gets reflected, only that a somewhat higher antenna will
radiate MORE energy that gets reflected.  I notice that you
did NOT have a comparison dipole antenna at 40 or 50 ft.

My bet is that a 40 or 50 ft high dipole would have beaten
your 20 ft high antenna.  Your example proves the theory
that "any antenna is better than NO antenna" but does not
prove that it is better than one which radiates ALL of it's energy
within the range of angles supported by the ionosphere.

One last comment.  ALL of my comments ASSUME
FLAT  TERRAIN.  Sloping foregrounds tend to favor
even lower antennas.

Tom  N4KG

> 
> 
> ----- Original Message -----
> From: <n4kg@juno.com>
> To: <TOWERTALK@contesting.com>; <swca@swbell.net>
> Sent: Monday, June 24, 2002 8:39 AM
> Subject: Re: [Towertalk] Re: [Force 12 Talk] XR dilemma
> 
> 
> > Hi Mark,
> >
> > I think our main disagreement comes over the the maximum
> > angle that is supported on 10M.  I believe that to be around
> > 20 degrees (at very high MUF's).
> >
> > Some time ago, someone plotted his 10M SS contacts on
> > a map.  The vast majority were at skip distances of 900 miles
> > or more, which corresponds to a 20 degree takeoff angle.
> >
> > At 18 ft, a 3L 10M Yagi places the majority of it's radiation
> between
> > 20 and 30 degrees.  3 dB points are 15 and 40 degrees.  Over
> > 80% of the energy is above 20 degrees, i.e. going into outer 
> space.
> >
> > At 35 ft, the 3 dB points are 7 and 22 degrees with the vast
> > majority of the energy falling in the range of angles supported
> > by the ionosphere.  I see NO BENEFIT in going lower than
> > 35 ft  on 10M.
> >
> > Tom  N4KG
> >
> >
> >
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> 
> 


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