Rich Adamson wrote:
clippage here
The -2 to -3 db is not correct for analog circuits. Copper wires have
a loss that is directly related to the length of the cable. (I don't
have the chart right here, but a 7,000 foot cable pair will have lets
say 6db of loss and a 3,000 foot pair will be a 3db loss. You can't
engineer something into a copper pair to compensate for that loss.)
The only thing that I can think of that you might be talking about is
using an old analog carrier system on a copper pair. If that's what
you're thinking, then yes -2 to -3 db is very reasonable.
Analog carrier was(is?) engineered for -16/+7 tx/rx TLP. That was
because microwave links liked it that way and it kept spurious emmisions
down.
What can be engineered into a loop is an odd little device called a pad.
Most often today they're found in the channel module in a channel
bank coming off of a digital switch. The milliwatt are accessed right
at the card and measured. the pad(s) on the card are adjusted for the
calculated values.
Analog switches were similar in that banks of pad sockets were wired to
the ports on the switch and plug-in pad/amp units installed and adjusted.
Then, on a "commercial" turn up (back when I did these, it was Western
Union and/or MCI), the tech at the other end would again dialup the
milliwatt, report the value measured over the loop and the pad(s)
re-adjusted to match the values for the loss in a document provided.
We spent a lot of time talking to telco guys who called down to the
frames to get a "shoe" put up in the frame so they could take their own
measurements. Watching telco field techs today, they still seems to do
it a lot the same way. I gues the exact equipment has changed, but the
process still seems similar.
If we were dependant on only the length and gauge of wire, as it was 70
years ago, that would be that. As it is, there are all sort of gadgets
they stick into pots loops. There used to be a device designated VRMN;
called vermin because that what we thought of them. I never saw one
physically, I only saw the effects of them. They were two wite,
bi-directional gain devices and when they went out of whack they did
totally insidious things to pots loops... Vermin!
Anyway, this is getting long.
_______________________________________________
--Bandwidth and Colocation sponsored by Easynews.com --
Asterisk-Users mailing list
Asterisk-Users@lists.digium.com
http://lists.digium.com/mailman/listinfo/asterisk-users
To UNSUBSCRIBE or update options visit:
http://lists.digium.com/mailman/listinfo/asterisk-users
