There are various antenna impedance matching techniques, and this is an elaborate and detailed subject.
Test equipment like Antenna Analyzer or VNA are required for proper impedance matching.
To know about these techniques:
(A) Please refer to ARRL Antenna Handbook.
From the links given below, you can download:
(1) Chapter 18 “VHF and UHF Antenna Systems” http://www.qrz.ru/schemes/contribute/arrl/chap18.pdf
(2) Chater 26 “Coupling the Line to the Antenna” http://www.qrz.ru/schemes/contribute/arrl/chap26.pdf
This is not the latest edition of ARRL Book, rather few years old edition, but contains good enough info about antenna impedance matching.
(B) Please refer to following web pages (You can find a lot more pages if you Google):
(http://www.rfwireless-world.com/Articles/impedance-matching-methods-circuits-devices.html)
(http://www.antenna-theory.com/tutorial/smith/smithchart6.php)
(http://www.ece.mcmaster.ca/faculty/nikolova/antenna_dload/current_lectures/L11_Match.pdf)
(C) Please refer to following posts for impedance matching technique I used
(there are many other good techniques available as well, which I have not tried):
(http://discussions.flightaware.com/post180415.html#p180415)
(http://discussions.flightaware.com/post205292.html#p205292)
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