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

[n4kg@juno.com]

On Mon, 24 Jun 2002 "Guy Olinger, K2AV" <k2av@contesting.com> writes:
> Actually NOT.
> 
> If you model it you will see that the pattern 3 db points on 
> elevation are 15 degrees through 75 degrees with a very broad maximum
around 
> 40 degrees. Straight up is a minimum on the pattern.

At 18 MHz, the highest angle supported by the ionosphere is
around 30 degrees, so ALL  of the radiation from 30 through
75 degrees goes into space.  Total WASTE of energy above 30 degrees.

> 
> This is a GENERAL PURPOSE height that scales well to other bands. It
> will behave the same as a 75 meter dipole at 93 feet or a 40 meter
> dipole at 50 feet.

At 7 MHz, higher angles are supported than an 18 MHz so higher
angle radiation IS USEFUL on 7 MHz whereas those same angles
go into space at the higher frequencies.

> 
> Also kindly remember that the point of the post was comparing this
> antenna with a C31XR on 18.1, a frequency not in the C31XR design. I
> was not trying to specify the killer antenna for 17 meters, just
> emphasize the degraded idea of using the C31XR for that band.

Resonance is NOT necessary for radiation.  I once convinced
a station in Africa to use his 15M dipole (and TH830) to work
me on 17 and 12M.  After those successes, he suggested trying
30M.  I expected the 15M dipole would not be very effective on
30M but was willing to give it a try.  We made contact and he
continued working the EU / NA pileup for an hour, giving out
the first 30M contacts with his country.

> 
> A 20 foot high backyard dipole for 18.1 MHz WILL beat trying to use 
> a C31XR, particularly at the end of nearly 700 feet of coax as 
> described by the original poster.

Are you SURE of this?  Based on what?

> 
> Dipoles get a lot of bad press. They really are a solid simple
> antenna. When the scores are added up at end of the contest, a lid
> with a beam will be thrashed every time by a good op with a dipole.
> Biggest db's of all are between the ears.
> 

The Dipole is a GREAT antenna. NO argument.  I have worked
over 320 countries on each of the WARC bands using nothing
but Dipoles of various kinds.  80M dipoles operate as current
fed long wires on the WARC Bands (~3/2 WL on 10 MHz, 
5/2 WL on 18 MHz, and 7/2 WL on 24 MHz).  One of my
favorite dipoles is a 20M (34 ft) center fed with Ladder Line
which exhibits a figure 8 pattern from 10 through 30 MHz.
GREAT ANTENNA (especially at 50 ft but NOT so great
at 20 ft as you recommended).

Tom  N4KG

> 
> ----- Original Message -----
> From: <n4kg@juno.com>
> To: <TOWERTALK@contesting.com>; <k2av@contesting.com>;
> <wa9als@starband.net>
> Sent: Sunday, June 23, 2002 7:29 PM
> Subject: Re: [Towertalk] Re: [Force 12 Talk] XR dilemma
> 
> 
> > On Sat, 22 Jun 2002 "Guy Olinger, K2AV" <k2av@contesting.com>
> writes:
> > >
> > > You would do considerably better on 18 MHz to just cut an 18 MHz
> > > dipole and string it 20 feet up in the air. Signals are quite
> strong
> > > on 17 meters.
> > >
> >
> > At 20 ft, MOST of the radiated energy will pass into outer space.
> >
> > As most readers of TowerTalk know, I strongly recommend 40 ft
> > as the minimum height for effective coverage of the upper angles
> > supported by the ionosphere on the High Bands (20 through 10 M).
> >
> > Tom  N4KG
> >
> >
> >
> > ________________________________________________________________
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> 
> 


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