[TowerTalk] FW: Moxon rectangles

[Keith Dutson]

Why is it important to know the exact impedance?  Could you just adjust the
hairpin or other matching circuit for minimum VSWR as read by your
transceiver?

Keith

-----Original Message-----
From: towertalk-bounces at contesting.com
[mailto:towertalk-bounces at contesting.com] On Behalf Of K4SB
Sent: Friday, March 25, 2005 10:20 PM
To: towertalk at contesting.com
Subject: Re: [TowerTalk] FW: Moxon rectangles

Tom Rauch wrote:

> I spoke against including a "resonance" function in the MFJ259. The 
> reason is you cannot measure resonance of an antenna through a length 
> of feed cable unless you know a great deal about the feedline.
> 
> All those who think they are measuring resonance of an antenna when 
> they measure zero X at the end of a transmission line without 
> understanding special qualifications are assuming incorrectly. The 
> only exception would be if the antenna was 50 J 0 at resonance, in 
> which case the feedline could still introduce false zero X crossings.
------
This may be a case of a simple ommision on Tom's part or an assumption that
the rest of us know as much as he does.

However, if you use an electrical 1/2 wave line connected to the antenna,
the impedence of the antenna will reflect exactly at the MFJ.

As a matter of course, I keep good quality RG58 lines for all bands just for
that purpose. I might also add that it does not matter what the
characteristic impedence of the test line is. Also, while constructing it,
if you use a high multiple ( such as 140 mHz ) for a 40 meter line, you get
a much sharper dip.

73
Ed
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