[Top] [All Lists]

[TowerTalk] "ZAGI" Configuration (MAGNUM 340 tuning)

To: <>
Subject: [TowerTalk] "ZAGI" Configuration (MAGNUM 340 tuning)
From: (
Date: Thu, 13 Nov 1997 07:33:16 -0800 (PST)
Good morning.

Am finally beginning to catch up a little on phone calls and e-mail and this 
one was towards the front of the stack. My apology for delayed responses to 
many of you, as things have been backed up due to a death on the family. 

"Zagi" is a term that came out of "unequal Z-axis Yagi." The Zagi has 
several advantages. One is that the effective height of the Yagi antenna 
(any Yagi) is essentially where the driver is located, so the effective 
height of the antenna is higher, without markedly increasing the windload 
(not having to raise the whole antenna). A second reason is that the 
effective boom length is longer, as the dimension from the driver to the 
reflector/director is the diagonal from the elevated driver to the 
parasitics. This also can position the driver for a "clearer view" of the 
relevant parasitics if the Yagi is a composite of two or more monobanders. 
Our common term "boom" has probably caused most thinking to move in the 
direction that the elements all must reside in a straight, horizontal plane. 
Such is not the case. 

The effect of the Zagi configuration is obviously more pronounced when the 
antenna height is not very high. The Zagi can be modeled using any software 
that allows for the driver to separately elevated. The highest elevation 
tested for a 40 mtr driver has been just over seven (7) feet for a 30' boom 
3 element. This antenna is often placed on a mast with other antennas, so 
the practical elevation is usually less than this, residing 4-5' above the 
boom. The driver tuning and match were readjusted slightly, as the coupling 
is not the same. On 80/75 mtrs, the highest elevation tested is the photo on 
the web page: the driver 14' higher and using a very short 34' boom for the 
remaining two elements. This antenna was run for almost a year and the 
increased effective height was quite noticeable, The effective boom length 
was really too narrow for a 3 element 80, but the primary testing was for 
the effect of the increased height.

The most practical use seems to be for a 3 element, simply because the 
driver can be raised on the mast. However, other configurations are 
obviously possible, especially using wire Yagis (for 80) where elevating the 
entire array is difficult. Installations utilizing roof mounts that desire 
more effective height without moving the entire Yagi to the top of the mount 
might fint the Zagi configuration attractive.

Have a good day and 73,
                        Tom, N6BT
                        Force 12 Antennas and Systems
                        (Home Page )

FAQ on WWW:     
Administrative requests:

<Prev in Thread] Current Thread [Next in Thread>