Yes. Although to generalize Barry's statements a bit, restricting the feedline
to a certain length 'moves' the antenna impedance to a different impedance
which is easier for the transmitter to handle. The SWR is not modified (other
than a small decrease due to line loss) but the impedance can be substantially
modified. Easiest to see and explain if one is familiar with Smith Charts where
it is very easy to see the effect of line length. The effect of using a certain
length of feedline might not be to move the antenna impedance to a purely
resistive one at the transmitter but might be to simply move the antenna
impedance to a more tractable one.
73
Bob Groh, WA2CKY
----- Original Message ----
From: Gary Smith <wa6fgi@sbcglobal.net>
To: Barry Kirkwood <barry.kirkwood@gmail.com>; amps@contesting.com
Sent: Thursday, October 11, 2007 8:12:33 PM
Subject: Re: [Amps] Trimming the transmission line
Is this the (possible) reason that Collins radio stated when using the
30-s-one to use exactly twenty feet of coax between the xcvr/xmtr and the
linear?
This info is one of the first cautions stated in the 30-s one install
instructions.
Just trying to keep on learning and understanding as I grow old and time
goes by.
73's,
Gary...wa6fgi
----- Original Message -----
From: "Barry Kirkwood" <barry.kirkwood@gmail.com>
To: <amps@contesting.com>
Sent: Thursday, October 11, 2007 4:30 PM
Subject: [Amps] Trimming the transmission line
> Have I got it wrong?
> As I see it:
> True: Changing the length of a transmission line will not change the SWR.
> True: It the SWR is other than !:1, trimming the line may bring one to a
> point where there is a voltage or current node, and the load will be
> resistive with no reactive component.
> 73
> Barry ZL1DD
>
> --
> Barry Kirkwood PhD ZL1DD
> barry.kirkwood@gmail.com
> _______________________________________________
> Amps mailing list
> Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
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