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Matching network for end-fed half wave, Q calculations etc.?
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January 6th 06, 07:16 PM posted to rec.radio.amateur.antenna
Roy Lewallen
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Matching network for end-fed half wave, Q calculations etc.?
An parallel LC network like you describe is usually made with L and C
having reactances of roughly 200 ohms or so. That generally gives a
loaded Q that results in good efficiency. As you suspect, the voltage
will be high at the end of the antenna no matter how you feed it.
Roy Lewallen, W7EL
wrote:
Hello:
I am contemplating a half-wave wire antenna for the 160m band and would
end-feed it against my roof as a counterpoise. If the wire length is
carefully trimmed I should get a high feedpoint resistance with
negligible reactance. Then comes the question of how to match this to
a 50 Ohm system.
The standard approach is using a parallel LC circuit and either make a
tap or a link for the 50 Ohm connection. In this case, how should I
select the L and C, as there are multiple choices leading to the same
resonance frequency but with different Q values. Any suggestions?
Or, would another matching network be more desirable, for example in
terms of loss? An L-network might do the job, but it is not
immediately clear to me if it would have any advantages or
disadvantages over the parallel circuit. Any comments?
I will be running substantial power into the antenna, so it is
important that the solution does not result in excessive losses (heat)
or voltages (although this will probably be inevitable at the
feedpoint).
73 - Kris, TF3KX
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