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
-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of Jim
Brown
Sent: Saturday, February 04, 2017 4:31 PM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] K9YC Choke Cookbook Question
On Sat,2/4/2017 12:55 PM, KD0Q-Glenn wrote:
> Several places in K9YC's material indicates that bifilar chokes wound
> with close spaced enameled wire would have an impedance of
> approximately 50 ohms and those wound with close spaced THHN would be
> 80-90 ohms.
This is correct.
BTW -- I first noted the Zo of these two chokes in a later version of Jerry
Sevick's (W2FMI) book. Quite a few years later, I built and measured
similar chokes and confirmed his results to reasonable measurement accuracy.
73, Jim K9YC
>
> In Chapter 7 of K9YC's "A Ham's Guide to RFI, Ferrites, Baluns, and
> Audio Interfacing" the table for bifilar chokes shows the THHN wound
> chokes at 50 ohms and 2/3 of those wound with enameled wire at 85 ohms.
This is a typo. Thanks for pointing that out!
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