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Re: [TowerTalk] PL259 Insertion Loss?

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Subject: Re: [TowerTalk] PL259 Insertion Loss?
From: "Paul Christensen" <>
Date: Sun, 15 Jan 2012 18:13:34 -0500
List-post: <">>
> With this setup, I could measure no significant losses. I am convinced
> (I convinced myself) that the "UHF connector loss" is a myth, right up
> there with that myth about the superiority of N-type at HF.

Probably a more relevant test is not to string a bunch of connectors 
together in series.  Rather, take the same number of connectors and place 
them at random points on say, 100 feet of low-loss line.  I think Steve's 
description (six ft. line sections connected with short Zo=100 connectors) 
accurately reflects what's happening, but it would be even more meaningful 
to look at SWR on the individual line sections between connectors as well as 
measure power delivered into a 50-ohm load at the end of 100 feet of line --  
then mix up the distances and record several different iterations at 28 MHz.

Speaking of non-constant impedance, consider the garden-variety monimatch 
SWR meter.  Crack one open and you'll see three bus bars, equally-spaced in 
a metal enclosure usually about five inches in length.  The inner bar is the 
transmission line inner conductor.  But the outer bars are used only for the 
sample; they don't contribute the characteristic impedance (Zo) of the 
monimatch.  Zo is formed by the inner bus and the metal box which results in 
a characteristic Z of probably several hundred ohms, certainly nowhere near 
50-ohms.  And yet, how many folks have inserted a monimatch SWR device at 
random points along the line, expecting near constant-impedance insertion?

The connector quality issue probably boils down to reliability and cost. 
However, in instances where the connectors are being used to accurately 
measure impedance and return-loss (e.g., VNA loads) then better connectors 
are needed as F increases.  For HF S11 reflection measurements into most 
line and antenna applications, it's probably a non-issue.

Just yesterday, I was bashing the Asian BNCs.  Not that I've changed my 
position, but even when a connector is so bad that return loss accuracy 
shifts from 70 dB to 25 dB, the final results are still fine for most 
antenna measurements.  But that amount of degradation tells me that if QC 
was poor at the time of manufacture, perhaps it's not a connector/adapter I 
want to use when I need it most.

Paul, W9AC


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