----- Original Message -----
From: "Paul Christensen" <w9ac@arrl.net>
To: <topband@contesting.com>
Sent: Friday, July 13, 2012 5:04 PM
Subject: Re: Topband: Mother of all ferrite common-mode coaxial chokes
>> One of the dumbest things I've seen recently from a very good company is
>> RF chokes in series with the shield connections on analog and RS232 I/O
>> boards for the Elecraft K3.
>
> Right. I think Joe, W4TV, was one of the first to identify that problem
> back around 2008. Many of us quickly jumpered the handful of RFCs used on
> shield leads of the RS232 I/O Board. Until revised by the factory, that
> board was the Achilles Heel of the K3.
>
>> Modern pro output stages have a very low source Z (typically
>> 100 ohms for line level) and high input Z (typically 10K for line
>> level), and consumer stuff is roughly 3-5X those values.
>
> Somewhere in my files from the late '80s is a white paper authored by
> Richard Cabot. I believe Richard was the chief designer of the Audio
> Precision brand of audio test equipment. The focus of the article was on
> the standarding of all audio output stages, balanced or unbalanced to a
> value of 40-50 ohms. He created models showing the effect of changing
> drive
> Z from 1-ohm through 600-ohms into long audio cables (and independent of
> terminating Z) that start to take on transmission line qualities. His
> conclusion was that a target of just under 50 ohms was optimum.
>
> Paul, W9AC
>
What does he consider a long audio cable Paul? Ive been using 600 Ohms to
run studio type equipment for the AM station.
Carl
KM1H
> _______________________________________________
> UR RST IS ... ... ..9 QSB QSB - hw? BK
>
>
> -----
> No virus found in this message.
> Checked by AVG - www.avg.com
> Version: 10.0.1424 / Virus Database: 2437/5129 - Release Date: 07/13/12
>
_______________________________________________
UR RST IS ... ... ..9 QSB QSB - hw? BK
|