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Re: [TowerTalk] Fwd: OT: Exterior Ethernet Cable

Subject: Re: [TowerTalk] Fwd: OT: Exterior Ethernet Cable
From: <>
Date: Tue, 12 Aug 2008 09:49:45 -0400 (EDT)
List-post: <">>

Not quite true...   

The most common cause of a change in VSWR measurement when you change the 
length of a coaxial transmission line is measurement error caused by poor VSWR 
bridge directionality.  Many inexpensive VSWR meters (and some expensive ones) 
suffer from this problem.

Please try this simple experiment with your VSWR meter, and let us know your 

  - Place your VSWR meter between your transmitter and a 100 ohm or 25 ohm 
resistive load.  Use short 50 ohm transmission lines to make the connections 
(less than 1/10 wavelength long).

  - Measure the VSWR.  If your VSWR meter is calibrated for 50 ohms, 
it should read 2:1

  - Replace the short cable between the VSWR meter and the resistive load with 
a 1/4 wavelength 50 ohm coaxial cable.  If your VSWR bridge has excellent 
directivity, the VSWR will not change from the measurement above.  If the VSWR 
changes, it was caused by poor VSWR bridge directivity.


---- Original message ----
>Date: Tue, 12 Aug 2008 08:49:15 EDT
>Subject: [TowerTalk] Fwd:  OT: Exterior Ethernet Cable  

> A simple test is to add (or  subtract) some of the coax between the SWR meter 
> and the antenna. 

> If you have a  change in the SWR you have current on the outside of the coax.

>Hans, N2JFS

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