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Re: [TowerTalk] K9YC Choke Cookbook Question

To: towertalk@contesting.com
Subject: Re: [TowerTalk] K9YC Choke Cookbook Question
From: Jim Brown <jim@audiosystemsgroup.com>
Reply-to: jim@audiosystemsgroup.com
Date: Sun, 5 Feb 2017 21:02:08 -0800
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
And with the easy availability of powerful test gear at relatively low cost, combined with AC6LA's fine Excel spreadsheets, it's easier than ever to get good data for VF and Zo vs frequency from a few measurements.

The procedure is pretty simple. Make swept vector impedance (that is, complex, magnitude and phase) of a convenient length of the line, one with the far end open, again with it shorted. Export that data to the spreadsheet, which will then compute and plot curves of VF, Zo, and attenuation vs frequency. The AIM family of analyzers will do this, and I believe the SARK will too. My weapon of choice is the VNWA 3e, designed by German university EE prof DG8SAQ and built by some hams in the UK.

The effect of a CCS conductor is clearly seen by comparing plots of mfr data for CCS cables on the same graph as for cables with a solid copper center. CCS line has more loss below 10 MHz than copper.

73, Jim K9YC

On Sun,2/5/2017 7:24 PM, Wes Stewart wrote:
If you follow this link http://k6mhe.com/n7ws/Ladder_Line.pdf to my paper and look at Table 1, it gives the measured values of four different Wireman P/Ns.

Note that these are 50 MHz values and transmission line Zo and Vp are anything but constant at lower frequencies. Likewise, these particular lines use copper-clad steel conductors that "misbehave" at lower frequencies so Eq 4 somewhat falls apart when the conductors do not have a well-developed skin effect. I mentioned this in the paper but did not account for it in the equation.

Wes  N7WS

 On 2/5/2017 5:11 PM, Hardy Landskov wrote:
Hi Jim and all,
The email below reminds me of a problem I had some years ago with "450 ohm window line". Nothing seemed to work. I then found an article that explained how to measure the Zo of coax/ladder line. I measured a piece of window line and it was 374 ohms! I found out in the archives that W8JI had measured 377 ohms with a piece of window line. We exchanged emails and he was elated that
I had verified his results.
Here you have two different sets of equipments, two different runs of ladder line, and different times. I was very happy myself. I have an HP8753B so it
was no problem to run through the numbers. It was a very eye opening
exercise!!
Bottom line: Use 375 ohms for matching tuners and other things when using
this line.
73 Hardy N7RT/4


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