[Boatanchors] 600 ohm lines / 70.7 volt distribution, etc.

[Jim Wilhite]

Actually the impedance of some of these lines changed over time in 
the ground on on the pole Dave.  Back in the mid to late 80s SWBT 
(now AT&T) was still using paper wrapped insulated cables between 
Greenville, TX and Dallas.  The phone companies are notorious about 
not replacing what the call "outside plant".  Rather they spent 
inordinate amounts of money to develop technology to gain bandwidth 
on existing installations, whatever that is.

So, like old resistors, the wire ages and the impedance goes up, 
giving you the ~900 ohm figure.  Even today, the equipment they 
employ must operate at maximum distance at impedances between ~200 
to ~900 ohms.

Jim/W5JO

----- Original Message ----- 
From: "Dave Maples" <dsmaples at comcast.net>

> Interestingly enough, standard terminating impedance for 
> residential phone
> lines is now 900 ohms, not 600.  That change was made many years 
> ago, I
> suspect with the introduction of the 500-series (rotary) phone 
> sets.  Anyone
> have some more history here?
> Thanks,
> Dave WB4FUR