Never mind, it was answered.
Carl
----- Original Message -----
From: "ZR" <zr@jeremy.mv.com>
To: "Paul Christensen" <w9ac@arrl.net>; <topband@contesting.com>
Sent: Friday, July 13, 2012 8:44 PM
Subject: Re: Topband: Mother of all ferrite common-mode coaxial chokes
>
> ----- 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
>
>
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