[GreenKeys] 88 mh toroids

[kf9nz at juno.com]

                        All very true, except that what I meant was, how
they were used in RTTY.   They were used to create two audio frequency
tune circuits; one mark and one space.  Toroids have very high Q which is
needed to make a tuned circuit narrow enough to give good selectivity at
audio frequencies 150 to 300 Hz apart. 
                        As for the original use of loading coils in
telephone circuits, it has gone the way of the vacuum tube.   My son-in
law spent a lot of time in manholes cutting out loading coils in toll and
exchange cables, but these days there are very few toll and exchange
cables.  Now he spends time pulling them out of ducts so fiber cables can
go in.    A few years ago telco's were going crazy looking for duct space
in big city streets.  Now they could lease duct space for water pipes. 
Telephone switching as I learned about it is ancient history.

Frankf9nz

On Fri, 17 Jun 2011 13:38:51 +0000 LARRY G <telegrapher at q.com> writes:
Well they are what's called in the telephone company "loading coils". 
they are put in cable pairs at various points throughout its circuit
depending on it's length.  The first load coil would be approx 3000 ft
from the central office and subsequent load coils would be every 6000 ft
thereafter.  Not all circuits have them, for example data, dedicated fax
lines and so forth.  They are meant for regular local telephone useage. 
What they do is reduce the loss in the cable pair if its a long loop by
inserting inductance which to an extent reduces the effects of resistance
and capacitance.  These elements cause loss if not compensated for. 
Probably the reason he had some extras is because he took them out of
some cable pair(s) on a jobn.  The cable pairs evidently were being
reclassified for a different type service or were going to be used for
underground carrier or maybe even digital purposes.  Those type circuits
would not work with load coils in them so they remove them.  WIthout a
load coil in a voice circuit such as your phone line between your house
and the central office where it connects to the rest of the world,
especially if it was over say 2 miles or more in distance, you would have
a hard time eharing and being heard at the other end of where ever you
were calling.  In short, they improve the quality of your phone service. 
With more and more facilites going the digital route, there is no longer
a need for them.
 
Larry
W0OGH

 
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