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From: floyd@icefog.polarnet.com (Floyd L. Davidson)
Subject: Re: What exactly does a loading coil LOOK like???
Date: 26 Dec 1997 14:39:12 -0900
Jim Fain <jimfain*nospam*@bellsouth.net> wrote:
>floyd@tanana.polarnet.com (Floyd Davidson) wrote:
>>Herb Stein <herb@herbstein.com> wrote:
>>>Ah! An interesting discussion. In Southwestern Bell territory,
>>>where Tim is, they use H-88 loading. That is 88 millihenry
>>>torroidal load coils. They are indeed spaced as Tim describes.
>>>There are also several other types of loading. I believe the
>>>44 mh version is called D-44 loading. It would require different
>>>spacing. I can look this stuff up if there is enough interest.
...
>>The "88" indicates an 88mH coil, the "H" indicates 6000 foot
>>spacing, and usually there is also a preceding number that
>>indicates the wire gauge.
>
>I'm with Tim. Here, the pairs are loaded at 3000 ft and then every
>6000 feet after that
>
>The way the engineers here talk about it, there is no other way to
>load! But it appears that is not the case.
Here are two charts for old Bell System designators, one for spacing
and another for inductance values.
LOAD SPACING LOAD COILS
LETTER SPACING NUMBER ACTUAL
DESIGNATOR FEET DESIGNATOR INDUCTANCE
A 700 18 18 Mh
B 3000 22 22
C 929 25 25
D 4500 31 31
E 5575 44 43
F 2287 50 50
H 6000 63 63
J 640 66 66
X 680 88 88
Y 2130 106 107
172 170
174 171
Different configurations have different uses, but either smaller
inductance coils or longer spacing will result in greater high
frequency cutoff points. Generally longer spacing is used with
larger coils. B-22 loading, for example, has a high frequency
response good out to 8kHz compared to about 3kHz for H-88
loading. The three most significant characteristics which
change when a cable is loaded, compared to non-loaded, are lower
loss, higher impedance, and lower bandwidth. There are other
changes too, such as lower propagation velocity, but those three
are the important ones.
The only commonly seen loading today is H-88, which provides
just enough bandwidth for a voice frequency circuit when used on
common 24 and 26 gauge cables. The other configurations are no
longer used because, since the concept of lump sum inductive
compensation for distributed capacitance began being applied in
practice just after the start of this century, many of the
listed configurations are intended for use with open wire and
other situations that are just no longer seen! That more or
less means even though all of these various forms of loaded
cable do exists, they are historical and in practice there is
really only one way to load a cable today.
Floyd
--
Floyd L. Davidson floyd@polarnet.com
Salcha, Alaska or: floyd@tanana.polarnet.com
From: floyd@tanana.polarnet.com (Floyd Davidson)
Newsgroups: comp.dcom.modems
Subject: Re: Is there a V90 that works?
Date: 2 Jan 1999 00:33:32 GMT
Steve Uhrig <suhrig@bright.net> wrote:
>Floyd Davidson wrote:
>> Steve Uhrig <suhrig@bright.net> wrote:
>>
>> Steve I know lots of phone companies that don't use loading
>> on 5 mile loops, much less 3 mile ones.
>
> Could you mention a few along with what area they do
>this in. Are they still using low cap cable instead of
There isn't a single loaded pair on all of Eielson AFB, near
Fairbanks.
In Fairbanks it is 50:50 that a long loop is not loaded. In the
rural area outside of Fairbanks, served from the PTI Com telco
in of North Pole, Alaska (the same telco that does the
commercial business at Eielson, though most of the cable plant
there is military) there are very few loaded pairs (I'm not in
any position to say none, but I was never aware of any.)
Clearly they rely on remotes to extend service, as they are
primarily a rural telephone company. They also are very heavy
users of subscriber line carrier systems.
When I lived in Salcha my lines were 4 miles by road (I'm not
sure what the actual cable milage was, but it would not have
been significantly greater), and one of them was cable carrier
while the other was copper with no loads on it.
Here in Barrow (GTE, by the way) my home line is more than
3 miles, and is not loaded. At work we have 2 miles of cable
between our facility and the CO, and there are no loads on
any pairs.
Arctic Slope Telephone Cooperative is the LEC in all of the
North Slope Borough villages, and while I'm not positive about
it (I've never had cause to look or to ask, though I will next
time it is convenient), I have seen no indication that they make
any use of loaded cable pairs. They have relatively few
locations with loops longer than 3 miles, and prefer other
solutions.
My exposure to LEC policy making machinery is fairly limited,
but it has been my understanding for the last 20 years or so
that loaded cable was intentionally being avoided if at all
possible. Prior to that it was very common to install cable
with loads, since then it has been rare in my experience.
Floyd
--
Floyd L. Davidson floyd@ptialaska.net
Ukpeagvik (Barrow, Alaska) floyd@barrow.com
Pictures of the North Slope at <http://www.ptialaska.net/~floyd>
From: floyd@tanana.polarnet.com (Floyd Davidson)
Newsgroups: comp.dcom.modems
Subject: Re: Is there a V90 that works?
Date: 4 Jan 1999 09:51:15 GMT
Steve Uhrig <suhrig@bright.net> wrote:
>Floyd Davidson wrote:
>> Steve Uhrig <suhrig@bright.net> wrote:
>> >Floyd Davidson wrote:
>> >> Steve Uhrig <suhrig@bright.net> wrote:
>> >>
>> >> Steve I know lots of phone companies that don't use loading
>> >> on 5 mile loops, much less 3 mile ones.
>> >
>> > Could you mention a few along with what area they do
>> >this in. Are they still using low cap cable instead of
>>
>> There isn't a single loaded pair on all of Eielson AFB, near
>> Fairbanks.
>
> Of course I don't know how big the AFB is but assuming
>that the switch was centrally located the base would
>have to be more than 7 miles across to even need
>loading on the pairs. Wright Pat AFB in Dayton Ohio is
Steve, bad assumption. The switch is located on one side of the
base. Eielson, geographically, might even be the largest USAF
base in the US... If it is not, that would only be because a
large portion of the Yukon Training Area comes under Fort
Wainwright's administration rather than Eielson's. It does have
the longest paved runway of any USAF base in the US. Just the
runway is long enough to require loaded cable under the rules
you are operating with. There are microwave systems between
various parts of the base. It isn't a small place and they do
have long loops. Very *long* loops.
>> Arctic Slope Telephone Cooperative is the LEC in all of the
>> North Slope Borough villages, and while I'm not positive about
>> it (I've never had cause to look or to ask, though I will next
>> time it is convenient), I have seen no indication that they make
>> any use of loaded cable pairs. They have relatively few
>> locations with loops longer than 3 miles, and prefer other
>> solutions.
>
> Is their plant buried? I would think they would stay
>away from aerial plant in the harsh climate up there.
Almost all aerial, because of the harsh climate... :-)
>If they don't have pairs over 3 miles they would not
>need to load. If their plant is buried, do they even
>bother to mark the load peds? We paint the tops of ours
>orange. Unless we run out of paint. The budget is very
I'll just look at their cable records.
>tight you know. They even notify security if you order
>batteries for the test equipment. Someone might take
>one home you know.
Screwing with employees here can make an expensive operation
suddenly become prohibitive. Sometimes the company needs
a battery, and the only one available is *mine*. The other
alternative will cost a few hundred dollars over the next
three days... Nobody worries about who owns the flashlight
a battery goes into.
>> My exposure to LEC policy making machinery is fairly limited,
>> but it has been my understanding for the last 20 years or so
>> that loaded cable was intentionally being avoided if at all
>> possible. Prior to that it was very common to install cable
>> with loads, since then it has been rare in my experience.
>
> If you have long copper loops you just can't avoid
>using loads if you want your customer to be able to
>talk on the loop. With the heavy use of subscriber
What you have described is known as the "Resistance Design"
plan, as opposed to one of several other various standardized
loop design plans. Unigauge and Long Route Design are two
others that are common.
However, my point is that while it might be the policy of GTE to
design outside plant *exactly* as you have described, that is
not the only way and there are many companies with very
different policies. Many operating companies simply do not use
loaded cable at all. They use other means to ensure a suitable
loop. Loop extenders, remote units, subscriber line carrier,
etc. etc.
In many places that has been a trend since about 1980, when
digital switching systems became widely available. The expected
use of digital loops is one reason. The lower cost of switching
equipment, making more frequently located equipment cheaper than
added cable is probably even more significant. The cost of
maintenance in some locations is even more significant. Cables
here are very unlikely to be installed with a splice box in a
manhole located every 6000 feet, for example.
Floyd
--
Floyd L. Davidson floyd@ptialaska.net
Ukpeagvik (Barrow, Alaska) floyd@barrow.com
Pictures of the North Slope at <http://www.ptialaska.net/~floyd>
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