[TowerTalk] 600 Ohm Line

[Daron J. Wilson]

Actually....the characteristic impedance of the phone wire is more like
100 ohms.  The overall circuit impedance should be at about 600ohms when
terminated and drawing current.  The reason the loading coils are added
to the cabling is the increase in capacitance in the line as it is
extended miles out there.  The inductance of the loading coil balances
out the high capacitance to keep the circuit impedance at a workable
level.

I think...

N7HQR

Daron J. Wilson, RCDD          ) )
Telecom Manager               ( (
LH Morris Electric, Inc.       ) )
(541) 265-8067 office       _|****|  mmm!
(541) 265-7652 fax         ( |    |  coffee!
(541) 270-5886 cellular     \|    |
daron.wilson at lhmorris.com    |____|
 

> -----Original Message-----
> From: towertalk-bounces at contesting.com [mailto:towertalk-
> bounces at contesting.com] On Behalf Of Rick Karlquist
> Sent: Thursday, July 29, 2004 10:26 AM
> To: Jim Lux
> Cc: towertalk at contesting.com; Jim Brown
> Subject: Re: [TowerTalk] 600 Ohm Line
> 
> Jim Lux said:
> > 600 ohms is pretty much a standard for audio balanced pairs. Think
about
> > it.. 3 kHz, the wavelength is around 100 km... I think you can
consider a
> > phone line (or audio cable) as a lumped component, not a
transmission
> > line.
> >
> 
> Turns out you can't consider the phone line as a lumped component
> even to get audio to the CO; moreover, the characteristic impedance
> is complex.  This is why the phone company has to use loading
> coils.
> 
> Rick N6RK
> 
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