Don:
What you are describing sounds like simply two 2-antenna systems placed 90
degrees to each other where on of the antennas is common to both. I
conclude that from your statement that there are 4 directions available. On
that basis the directionality of the systems is a cardioid pattern which has
a 120 degree wide lobe at the half power points.
I have not seen the pattern for the equilateral array but based on the
materials I have seen, that pattern has a 60 degree wide lobe, so it is
hard to believe that the gain difference is only 0.2dB. The cardioid
pattern is indeed directional, hence the use for many years in the
non-directional beacon system for aircraft (relying in that case on the null
in the opposite direction). However the forward gain is rather modest. The
formula for that pattern is (1+coswt) which translates to 2.0 where wt=0
degrees and 0 where wt=180 degrees. Thus the front to back is very good but
the forward gain is just modest.
Does anyone have the gain for the equilateral array?
73
Bill
W7VP
----- Original Message -----
From: "Don Havlicek" <n8de@thepoint.net>
To: "Ian White GM3SEK" <gm3sek@ifwtech.co.uk>
Cc: <towertalk@contesting.com>
Sent: Wednesday, April 05, 2006 8:36 AM
Subject: Re: [TowerTalk] Phasing verticals and stubs
> Comments inserted below:
>
> Ian White GM3SEK wrote:
>> Don Havlicek wrote:
>>
>>>The 'right triangle' system utilizes two verticals per selected
>>>direction with the third 'floating'. The 'equilateral triangle' system
>>>uses all three verticals simultaneously,
>>
>>
>> Any triangle system can be used with either two or three elements
>> energized - check with ON4UN's book for details. In either case, the
>> most practical and versatile system for beam switching is the
>> equilateral triangle.
>
> Most practical? It requires separate control line for .2db additional
> in any one direction, but narrows the beamwidth [with reference to
> 1/2-power points] to do this, making signals +/- 60 degrees much lower
> in intensity than the right-angle system.
>
> Versatile only in respect to that .2 db gain and beam 'pointing'.
>
>>
>> When only two elements at a time are used (the third being
>> disconnected), an equilateral triangle gives three directions along the
>> sides. With three identical elements and ground-planes, you have easy
>> reversal for a total of six directions.
>
> Easy reversal - with a separate control line and more phasing lines.
>
>>
>> When all three elements are used, usually one is driven with 100%
>> current, and the other two are driven at the same phase with about 50%
>> current each. The beam directions are off the top or the bottom of the
>> triangle (so they are moved around 60deg compared with the two-element
>> case). The gain is higher using all three elements, but beam switching
>> is much less simple so you may be practically restricted to only three
>> directions.
>
> Yes ... much less simple.
>
>>
>> Any right-angled triangle would be less versatile than either of these
>> equilateral cases.
>
> Absolutely NOT less versatile. Look at the beam pattern for a
> two-element array fed 90 degrees out of phase and spaced 1/4 wavelength.
> Then place FOUR of these patterns around the origin of the plot at 90
> degree rotation. Notice that all directions are covered with less than
> .5db reduction from the center of the beam pattern.
>
> Being able to do all the switching over the coax with ONE phasing line
> makes for a very simple array.
>
> Don
> N8DE
>
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