George,
Normally, the maximum current a central office would source is 100 mA.
And that's if the central office to customer modem distance was short.
(short loop, less resistance).
As for FCC Part 68, there are no performance requirements relating to
loop current. All Part 68 is intended for is to prevent harm to the
network and network personnel.
As a side note, if this modem was to be designed for France, it would
have to internally limit the current to 60 mA.
I would be concerned about how many lines had to be modified. What
value attenuation was used by the technician? When is the problem
taking place? (ie dialling, handshaking, data transfer?) Are the
signals strong enough after the attenuator to be reliable?
If the modem passed Part 68, the signals should not be too strong.
Normal inband strength is 0 dBm (1 milliwatt/600 Ohms) 3 second
averaging for dialling and -9 dBm for data. These measurements should
be made at 20 to 100 mA of loop current. If the signal dies at high
loop currents, it is not a Part 68 issue.
Eric Petitpierre
Pulsecom
Herndon, VA
[email protected]
______________________________ Reply Separator _________________________________
Subject: current on the phone line ?
Author: [email protected] at smtp
List-Post: [email protected]
Date: 11/22/99 8:43 AM
> Hello All,
>
>
> We manufacture a modem product which has been tested and found to comply with
FCC part 68 (& CS03).
>
> At a customer site, (a CO in Pittsburg) an installer was setting up our modems
on a phone system and the modem would not communicate on the lines. It was dete
rmined ( by the site tech) that there was more line current on the phone line t
han our modem
could handle and a resistor (attenuator) had to be put on the lines so it
could
function normally.
>
> Since Part 68 deals only with signal / levels that our equipment imposes onto
the network, my question is:
>
> Is there a standard out there that:
>
> 1) defines what the acceptable line levels are or should be ?
> 2) defines such requirements for Modems ?
> 3) prescribes appropriate testing to ensure proper operation at higher than le
vels ?
>
> Am I making sense ??
>
> I would appreciate any help from you.
>
> Thanks,
> George
>
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