[TowerTalk] how do you model a hairpin match?

[Jeff AC0C]

The hairpin match is a feature provided in AutoEZ.  If you are a hardcore 
EZNEC user, check out AutoEZ.  It’s a spreadsheet based optimization front 
end for EZNEC that's written by Dan AC6LA.  He's the guy who made ZPLOTS.

73/jeff/ac0c
www.ac0c.com
alpha-charlie-zero-charlie

-----Original Message----- 
From: john at kk9a.com
Sent: Friday, May 22, 2015 2:27 PM
To: towertalk at contesting.com
Subject: Re: [TowerTalk] how do you model a hairpin match?

I have no experience modeling a match. The modeling method described in
your last paragraph should give you the correct SWR curve however I do not
think that it will give you the exact driven element length when using a
hairpin. It would be correct if using a balun transformer. I think that
you will still have to shorten the element when you add a hairpin match to
the antenna.

John KK9A


To: "tower" <towertalk at contesting.com>
Subject: [TowerTalk] how do you model a hairpin match?
From: "StellarCAT" <rxdesign at ssvecnet.com>
Date: Fri, 22 May 2015 13:23:44 -0400

Ok.... I read the Antenna Handbook... it says to use a chart they have –
reading it at 52 ohms line impedance (coax)... and 22 ohms RL I need 42
ohms of
reactance.
Then shorten the driven element to produce enough capacitive reactance to
cancel out the inductive and transform the impedance up to 52 ohms.

So I enter 42 ohms as a center load in my driven element (6ft/-6ft length
load
set to 50% and is 50% ... ) ... then shorten the length of the driven
element.
But this doesn’t work. The load never gets transformed.

What I’ve been doing is enter their length/diameter info from their 
manual...
then adjust the driven element to get the SWR where I need it (centered) ...
then I read the load resistance off the SWR chart and change the “alternate’
source impedance to be this value. Finally I add in just enough hairpin to
cancel out any capacitive reactance. This works – I get the same SWR curves
that are published by M2 when I model their antennas... so I know its
‘right’.
But I can’t seem to now NOT use the ‘switch’ to a different line impedance 
in
order to determine the correct hairpin XL so I can figure out how to build
the
hairpin!

any one see what I’m doing wrong please?

This is using EZNEC5

Gary
K9RX

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