[ProAudio] Western Electric 111C transformers

Jim Brown jim at audiosystemsgroup.com
Wed Feb 2 11:09:43 PST 2022

On 2/2/2022 6:32 AM, Scott Dorsey via ProAudio wrote:
> It wasn't as bad as you'd think since the frequency-dependent loss of the
> lines was minimum phase and so would be corrected by a minimum-phase
> equalizer that flattened the frequency response.

What is not generally realized is that there are extreme variations in 
VF (velocity of propagation) and Zo (characteristic impedance) through 
the audio spectrum. They are characteristic of ANY transmission line, 
predicted by the full form of the wave equation. As part of research 
I've been doing for some ham radio applications, I've done sweep 
measurements of more than a half-dozen cables, both coax and 
close-spaced 2-wire line, and all clearly show the variations. My 
instrumentation is a Vector Network Analyzer.

from the earliest days of telephony, equalization applied to long lines 
was as least as important to correct for variations in VF as it was for 
amplitude rolloff. I adapted and expanded on a paper by James Hayward, a 
retired engineer from Canadian telco who I met through Neil Muncy. I 
wrote this in 2005 to debunk some of the mythology that had been 
circulating at the time.


Jim Brown

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