[CQ-Contest] Which would make better stubs?
W4EF at dellroy.com
Sat Nov 5 09:34:37 EST 2005
----- Original Message -----
From: "k7qq" <k7qq at netzero.net>
To: "CQ-CONTEST" <cq-contest at contesting.com>; <mwdink at eskimo.com>
Sent: Friday, November 04, 2005 8:58 PM
Subject: Re: [CQ-Contest] Which would make better stubs?
> I've never heard of this LMR400 stuff, If a stub is being made for HF
> 213 is more than adiquate.
> After all it is a Stub to absorbe harmonics, even lossy old RG 11
> work, Just use ur handy dandy 259b to tune it.
Stubs actually alternately create an open circuit (at the operating
frequency) and a short circuit (at the harmonic) via reflection. They
don't actually absorb the harmonic. In the absurd limit as the stub
coax becomes very very lossy it will look like nothing more than a
50 ohm resistor shunted across the main tranmission line, where in
a matched system is would have 3dB of loss at the operating frequency
and 3dB of loss at the harmonic. At the other end of the spectrum
(a perfect lossless transmission line), the stub will create a perfect
open circuit at the operating frequency which when shunted across
the main transmission line will have no effect (e.g. zero insertion loss)
and a perfect short at the harmonic which when shunted across a
source with finite output impedance will cause infinite attenuation.
BTW, RG-11 isn't all that lossy as transmission lines go. It would
probably make a decent stub.
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