On Jan 25 14:53 96, Stephen Lennie of 3:640/101 wrote:

SL>  * Crossposted from: NetComm Support Conference

SL> G'day All!

SL> NetComm SmartModems use a telephone cord with a piggy-back type plug on the
SL> end which seems to perform exactly the same as a standard (MODE 1) double
SL> adaptor except that it has, what appears to be, a capacitor between pins 2
SL> and 6.

>> AUSTEL PERMIT NO: A90/831/0179

One to watch.

SL> [SOCKET end]                          

SL> 1  2  3  4  5  6
SL> |  |        |  |
SL> +--|--------|--|--- \
SL> |  +--------|--|---  \ [to MODEM]
SL> |  |        +--|---  /
SL> |  |        |  +--- /
SL> |  +---||---|--+
SL> |  |        |  |
SL> 1  2  3  4  5  6

SL> [PLUG end]

Is this cable permanently attached to the modem, or connected via a RJ plug
and socket?

SL> I called NetComm and they confirmed that it was, indeed, a capacitor and 
SL> that it was used to regulate power on the phone line but couldn't/wouldn't
SL> tell me much more than that.

In that position, it would be part of the ring load, and possibly intended
as the reactive component of a complex impedance presented to line.

They're -supposed- to provide the "option" of having 600 ohms
resistive. Wired into the plug, this can't be done if the cable's not
detachable.

Does the manual detail the operational requirement for when to, and when
not to, use this attachment?  (It should.)

Note: they're telling consumer oriented tales - "regulate power"
it certainly doesn't.  However, it is a credible story to tell a
non-technical person with moderate hopes of leaving 'em marginally better
informed than before.

SL> The capacitor is a black cylinder approx. 10mm long and 5mm in diameter 
SL> with a "thick" (1.5mm diameter) metal lead wire coming
from each end.
SL> The  following lines of text run lengthwise around the capacitor:

SL> [company LOGO - unknown to me]
SL> 1.5KE
SL> 200
SL> CP
SL> C314

SL> Can anybody tell me what type of capacitor and what rating it is?

It's trying to tell you that it's a 200v, 1.5k surge rated 31000 pf
capacitor, if I correctly understand the coding.  It will almost certainly
be a metalized mylar self-healing type, suited to direct connect across
ring voltage and possible line incidents.  If the engineer did his design
calculations correctly, there's almost nothing you can do to improve it.

SL> Also, how does it function - is it designed to hold the line at 50V or just
SL> smooth out occasional dips?

None of the above.  It applies to AC only, (It's a capacitor, right?) and
its primary purpose has to do with the impedance the modem represents to
the line.
(This matters - balanced bridges are an essential fact of modem and telecom life.)

It has effect in the load placed on ring voltage, and in the balance
achieved in your line card hybrid at the exchange.  Both at AC.

The 50v DC current source isn't affected, except during transients, like
when the modem is first plugged in.

SL> Any help appreciated, thanx.

Not too much help available, sorry.

Regards,
Dave Hatch.

--- Msgedsq/2 3.20