🚀 go-pugleaf

From: Jeff.Lindstrom@ofa123.fidonet.org (Jeff Lindstrom)
Newsgroups: sci.electronics
Subject: Cable losses
Message-ID: <577@arrlhq.UUCP>
Date: 14 Apr 1992 11:14:08 GMT
Organization: Universal Electronics Inc. (Public access BBS)
Lines: 19
 
U>Shouldn't the long cable attenuate the signal or even roll of the high
U>frequencies?
 
>  It IS attenuating the signal, but too little to notice for the low frequencie
>s you mentioned and the moderate cable lengths you are using.
 
U>How can I determin the maximum cable length before signal degradation begins?
 
>  First, determine an acceptable degradation.  Then look at the specs for the c
>able you wish to use.  The major loss will be distributed capacitance (commonly
> expressed as picofarads/foot or nanofarads/foot).  Multiply by the cable lengt
>h and take the RC time constant from the circuit (can you say Thevenin's Rule? 
> I knew you could.).
 
This isn't the way to do it, because the cable also has distributed 
inductance which cancels out the distributed capacitance.  Incidentally,
cables with a silver plated steel conductor(s) sometimes have much higher loss
than you might expect, because the silver is so thin that skin effect
degrades the lower frequencies.  It has been pointed out to me that 
the actual dielectric losses of both teflon and polyethylene are pretty
much negligible, though this may change if we actually get to see cables
made out of superconducting materials.  For now, the resistive losses are 
of primary interest below 1 GHz.


> Another source for degradation is outside noise coming through the shielding.
 > That will be a function of the shield's construction.
 
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Jeff Lindstrom
Internet: Jeff.Lindstrom@ofa123.fidonet.org
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