|To:||Jan Erik Holm <email@example.com>,"'towertalk'" <firstname.lastname@example.org>|
|Subject:||Re: [TowerTalk] 4 SQ WX0B box|
|From:||Jim Lux <email@example.com>|
|Date:||Thu, 18 Nov 2004 11:33:42 -0800|
At 05:28 PM 11/18/2004 +0100, Jan Erik Holm wrote:
Looking at the photo, I'd imagine it's a set of multiple LC networks, rather than a single network as used in the W7EL. This lets you do a bit better job synthesizing the phases, and potentially could remove the requirement for 1/4 wavelength lines, which creates a bit of a installation problem. For instance,you could use 1/2 wavelength cables.Just checked the WX0B website and his 4 SQ box. As far as I remembered it used to use the Lewallen current forcing method however now he is talking about "the new Lahlum" method. Anyone know what that is? Sure looks like current forcing to me. Or do I have to wait until 2005 to read it in ON4UN´s book.
Unfortunately, the manual is a dead link(404), so I can't comment further.
This is a good compromise solution when you want to have your switching centralized, and with a reasonably symmetric array. You do have potential loss from circulating currents in the feedlines. The reactive component to cancel the feedpoint reactive component is back at the box, so the reactive power is carried in the feedline. In an ideal system, you'd have the reactance at the antenna, so that the feedline is at 50 ohms, and all the box needs to do is generate the right phases. Of course, the matching network at the antenna would then need to have multiple values, since the feedpoint impedance changes with the array steering direction. And, it would be quite "challenging" to tune up (broadcast antenna engineers earn their pennies doing this).
It would also make the total system cost higher.
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions and ask for Sherman, W2FLA.
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