[Amps] Trimming the transmission line

[rgroh at swbell.net]

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 at sbcglobal.net>
To: Barry Kirkwood <barry.kirkwood at gmail.com>; amps at 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 at gmail.com>
To: <amps at 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 at gmail.com
> _______________________________________________
> Amps mailing list
> Amps at contesting.com
> http://lists.contesting.com/mailman/listinfo/amps 

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