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@contesting.com>
Subject: [TowerTalk] how do you model a hairpin match?
From: "StellarCAT" <rxdesign@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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