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Re: [TowerTalk] 6M Transmission Line

To: towertalk@contesting.com
Subject: Re: [TowerTalk] 6M Transmission Line
From: Jim Brown <jim@audiosystemsgroup.com>
Reply-to: jim@audiosystemsgroup.com
Date: Fri, 19 Jul 2013 08:39:19 -0700
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
On 7/19/2013 7:59 AM, Hector Garcia XE2K wrote:
There is no problem to run the LMR-600 ,  if you are sure you have the 75 ohms version  
you can "adjust" for 50 ohms

There is a simple, but tried and true method for using 75 ohm cable to feed a 50 ohm load. Simply make the 75 ohm line an EXACT multiple of half-wavelengths at the operating frequency. This works because the impedance transformation that happens in any transmission line comes back to where it started every half-wavelength.

Getting the length right is also easy -- put a connector on one end and measure the impedance using any antenna analyzer with the far end shorted. When it's an exact multiple, it will measure as a short. To calculate the length, use the velocity factor of the coax and cut it a little long, then trim until it's right.

73, Jim K9YC
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