W4SAV wrote:
> Well, my original statement is not 100% true for all heights, and
> neither is yours. Here are some EZNEC numbers for a three
> element Yagi turned either vertically of horizontally.
Even at 20 meters, 150 feet or more is a bit out of reach for most
people. However, your statement is correct at heights that begin
to approach free space conditions (5 to 10 wavelength). With those
heights horizontal antennas loose their "ground reflection gain"
and the vertical antennas lose the ground losses (which are not
reflected in your models).
When one reaches true free space conditions, the antennas will
have identical gain but amateur HF antennas are located in the
real world (above ground) unless your station is located on ISS.
73,
... Joe, W4TV
> -----Original Message-----
> From: towertalk-bounces@contesting.com
> [mailto:towertalk-bounces@contesting.com] On Behalf Of K4SAV
> Sent: Wednesday, June 20, 2007 11:01 AM
> To: towertalk@contesting.com
> Subject: Re: [TowerTalk] Trapped Tribanders Turned Vertical
>
>
> K4SAV wrote:
> The higher the antennas are, the less difference in gain
> there will be between mounting vertically and horizontally.
>
> W4TV wrote:
> Not true ... the vertical beam will always miss the "ground
> gain" and will lag the horizontal antenna by three to six dB.
>
> ------------------------
> Well, my original statement is not 100% true for all heights, and
> neither is yours. Here are some EZNEC numbers for a three
> element Yagi turned either vertically of horizontally.
>
> Height ___ Horz Antenna ______ Vert Antenna ____ Gain Difference
> 20 ______ 9.6 dBi at 36 deg ___ 4.8 at 17 deg ______ 4.8 dB
> 30_______11 dBi at 28 deg _____ 5.7 dBi at 15 deg __ 5.3 dB
> 35 _____ 11.6 dBi at 25 deg ____5.9 dBi at 13 deg __ 5.7 dB
> 40 _____ 11.9 dBi at 23 deg ___ 6 dBi at 12 deg ____ 5.9 dB
> 80 _____ 12.7 dBi at 12 deg ___ 8 dBi at 9 deg _____ 4.7 dB
> 100 ____ 12.9 dBi at 10 deg ___ 8.8 dBi at 8 deg ___ 4.1 dB
> 120 ____ 12.9 dBi at 8 deg ____ 9.4 at 7 deg _______ 3.5 dB
> 150 ____ 13 dBi at 7 deg ______ 10.1 dBi at 6 deg __ 2.9 dB
> 200 ____ 13.2 dBi at 5 deg ____ 10.8 dBi at 5 deg __ 2.4 dB
> 300 ____ 13.1 dBi at 3 deg ____ 11.6 dBi at 3 deg __ 1.5 dB
>
> When a horizontal antenna is placed very close to the ground, like 35
> feet or less for a 20 meter antenna, the ground loss for the
> horizontal
> antenna increases dramatically making my original statement
> not exactly
> accurate. However, above about 40 feet, the gain difference
> between a
> horizontal and vertically mounted antenna steadily decreases.
>
> Jerry, K4SAV
>
> Joe Subich, W4TV wrote:
>
> >>The higher the antennas are, the less difference in gain
> >>there will be between mounting vertically and horizontally.
> >>
> >>
> >
> >Not true ... the vertical beam will always miss the "ground
> >gain" and will lag the horizontal antenna by three to six dB.
> >Over salt water the vertical beam will have more gain at
> >lower take off angles but its maximum gain will never equal
> >that of the same beam mounted horizontally.
> >
> >A good frequency for comparison is 10 meters as the height
> >required for a horizontal antenna to have a take off angle
> >similar to that of the vertical antenna becomes reasonable.
> >A vertical dipole at 55' (center) over perfect ground (salt
> >water) has a peak gain of 4.13 dB at 7 degrees. A horizontal
> >dipole at 55' has a peak gain of 8.08 dBi at 9 degrees (7.63
> >dBi at 7 degrees). Move the antennas to 70 feet and the
> >gains are 4.71 dBi for the vertical dipole and 7.92 dBi for
> >the horizontal dipole (at 7 degrees).
> >
> >73,
> >
> > ... Joe, W4TV
> >
> >
> >
> >
> >
> >
> >
>
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>
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