[TowerTalk] Mystery hardline

[Robert Chudek - K0RC]

Guy,

No, I don't have a clue what it might be. It's kind of like asking "I've got a set of four black tires with white sidewalls on one side of them. Will they work on my car?"

But you can test the coax and get a rough idea about the impedance by putting a 50 ~ 52 Ohm resister at the far end and measuring the VSWR. If it's 1:1 that would tell you it's a 50 Ohm impedance. If it's 1.5:1 that would suggest a 75 Ohm impedance. Or you could put a 100 Ohm potentiometer at the far end and adjust it for minimum VSWR, remove the pot, and measure its resistance. That will be the approximate impedance of the cable.

If you have (or can borrow) an antenna analyzer (MFJ259), you can short the far end and measure the lowest frequency of the VSWR dip. Then you can calculate the velocity factor by measuring the physical length compared to the free-space (calculated) length. This will give you the ratio between the two (i.e., the velocity factor).

With a couple basic tools, you should be able to determine what you need to know. It's a good problem to have that will teach you about RF and some basic measurements. You can Google "measuring unknown cable impedance" and find more specific details.

73 de Bob - KØRC in MN



Message: 4
Date: Tue, 2 Nov 2010 06:15:28 +0000
From: Guy Molinari<guy_molinari at hotmail.com>
Subject: [TowerTalk] Mystery hardline
To:<towertalk at contesting.com>
Message-ID:<BAY129-W16905245A9B5BD0978CBAE8490 at phx.gbl>
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I picked up some surplus hardline.   It has an OD of 5/8" including a 1/16" plastic jacket.   The jacket is black and has a green stipe running up 2 sides of the cable.

Any idea of what this stuff is?   Specs?

73,
Guy, N7ZG 		 	   		

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