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Re: [RFI] Auto quieting

To: rfi@contesting.com
Subject: Re: [RFI] Auto quieting
From: Jim Brown <jim@audiosystemsgroup.com>
Reply-to: jim@audiosystemsgroup.com
Date: Sun, 11 Oct 2015 09:39:23 -0700
List-post: <rfi@contesting.com">mailto:rfi@contesting.com>
On Sun,10/11/2015 5:51 AM, Howard Lester wrote:
What am I missing here? Zip line is not coaxial; it is "balanced" line and
requires a transmatch. With a simple transmatch you get the SWR down to 1:1
and you're all set.   ?

What you are missing is the fundamental physics of how transmission lines work. The SWR is determined by the match between the antenna and the line, not between the transmitter and the line. Second, the major problem is not mismatch, it is the high loss in zip cord at RF. The mismatch adds slightly to that loss.

You are also missing the fact that "balance" in a system is defined by equal impedance to the reference plane, usually earth or circuit common. Parallel wire line is not "balanced," it simply does not CAUSE imbalance. There's nothing inherently bad about imbalance in an emergency situation, but burning half you TX power when you're starting out with low power CAN be a problem.

I don't object to saying that we CAN use zip cord as an improvised feedline. I DO object to calling it a GREAT solution. That part is urban myth, and it's wrong.

73, Jim K9YC
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