Don Bruder said:
Hell, The folks three miles further up the road from me are ALL on
pair-gain equipment. Which, I'm told by the phone guys who have shown up
at my place to fix problems, is the reason that they count themselves
lucky to get a 2400 (yes - two, four, zero, zero) bps connection when
they try to dial into an ISP.
"Pair gain" may mean different things to different folks. For example audio
gain amplifiers and/or inductive 'loading' coils, typically 88 millihenry
added at distances of, IIRC, each 6000 feet to improve voice pair losses, on
very long telephone loops. That treatment works up to an analog frequency of
around 3500 hertz! Loading, while reducing the lower frequency loss, in
particular, 'cuts off' higher frequencies due to the added inductance,
limiting bandwidth.
A company I worked for did various pair gain work when a local US military
base closed down. It's USAF private branch exchange was taken out of
service. Following that subscribers in the base area, wanting telephone
service were connected on very, very long loops to the private telephone
company serving the civilian community some distance away.
To improve telephone voice transmission various audio gain devices were
added; even so the loops had very high resistance, which could affect
signalling/dialling, especially back in the old rotary dial days!
We don't get much really hot weather here; but on one or two exceptional
days the resistance of some copper wires, inside the overhead black jacketed
cables increased to the extent that telephone dialling failed; just couldn't
get dial tone. At night things cooled down and telephones worked again!
However 'pair gain' can also mean adding devices such as a 'subscriber line
carrier'; this is often a transistorized device which mounted at the telco
main frame and out on pole or in someone's house etc.. uses low frequency
'carrier' signals over existing cable pairs which are already in use. This
is done to avoid, say, installing any more cable on existing fully loaded
pole structure or in already full underground conduits! In other words this
'gains (the equivalent of) more pairs'!
I seem to recall that such devices could be installed quickly for about
$125; heck of a lot cheaper and quicker than running, say 5 miles of cable.
So, for example, YOUR main phone might be on a cable pair; but that pair
may also be used via one of those devices to provide telephone service, just
POTS (Plain Old Telephone Service) to Mrs Smith two doors down. Naturally
while the telco has met its obligation to provide telephone service such
methods mean very poor bandwidth, both on the pair itself and the added
service. Conditions which tend to require the use of pair gain devices tend
to be farthest out from telephone company switching exchanges or 'wire
centres' and/or are 'pockets' of residential development!
Our telco here will not provide DSL service beyond certain defined limits;
they will however do a test if the area is considered marginal or the
customer insists.
Our DSL comes about one kilometre over the same pair as our standard home
telephone. As mentioned if the telco has to special conditioning, amplifiers
rearranging of pairs in order to get DSL to work, it can get expensive. I
have acquaintances who live just too far out in the country, as it were, to
get DSL for the foreseeable future.
