Friday, May 10, 2019

The ZL Special directional array

Yesterday we discussed the W8JK bidirectional array.

I suggest reading that now if you haven't done so.

The gist of the W8JK is that it's a two element bidirectional antenna. Both elements are spaced about 1/8 wavelength apart. Both are driven, with a 180 degree phase shift between the two. This is done by reversing the polarity to one of the elements.

What happens if you try other phase shifts? The answer is that the antenna becomes unidirectional like a yagi. Although they won't have any more forward gain than a 2 element yagi, there may have a deeper null off the back. That can reduce interference pick-up. Maximum front to back ratio happens when there's a 135 degree phase difference between elements. That configuration is sometimes called a 'ZL Special'. While the most common arrangement has two elements, people have added more for higher gain, particularly on VHF.  

Intrigued? Read more about ZL Specials here: 

* The 'BRD Zapper - A quick and easy ZL Special
The '8JK revisited and the 'BRD zapper
* Jonathan Hare's ZL special for the 2m band
* VK2ZIW ZL Special for 6m
* W4RNL on the ZL Special & more here
* JA6HIC's ZL Specials
* W7EL's FD Special

PS: Do you sometimes come across terms that you're unfamiliar with? The Illustrated International Ham Radio Dictionary can help. Available in both ebook and paperback it's great value. Find out more here

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