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.

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

SL> How (if at all) would this affect the modem's performance?

It should be factored into the line equalizer.  It's a reactive component,
and it must be allowed for in the phase and amplitude calculations.  In
engineering gobbldegook, it's converting a line interface from an
"L" pad into a "Pi" section, plus adding a filter pole.
 Why, I wouldn't know without enough data to rebuild the original design
equations.   Since the modem works, the math was at least approximately
correct.

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

SL> The cable's detachable but it's (capacitor) still wired into the plug.

The "option" would have to be a second cable.  Possibly intended
to be an extra orderable part.  Compliant - just.

SL> I've noticed that many modern phones can be set to either NORM (normal) or
SL> 600 Ohms and this is supposed to affect the sidetone, but I've only seen
SL> references to the 600 Ohm resistance when connected to *some* PABXs.

According to Telstra engineering, occasionally this is desirable for modem
use.  I did not get an intelligible (to me) rationale for just when/how to
tell, this would be the case.

SL> If I toggle this switch on my phone the sidetone is slightly louder and
SL> slightly higher pitched, but no great difference.

Audibly, it certainly wouldn't make much difference.  The
"louder" has to do with your exchange hybrid being balanced for
the selection you're normally in, and coming unbalanced and leaking a bit
more back when you change over.

A modem is an order of magnitude more fussy - ESPECIALLY - these blasted
full duplex echo cancelling wunderkind.  (Read v32 and up.)

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

SL> The cable originally came with my NetComm M7F but I continued to use it 
SL> with
SL> my M34F because it has the piggy-back plug - very handy.  NetComm say that 
SL> it
SL> doesn't matter what (recent) model of NetComm modem I use the line cord 
SL> with.

The design engineer would probably turn pale and faint at the thought. :-) 
Still - if it works well, go with it.

SL> The cable came with the M7F as the standard telephone line cord, with a
SL> 605/610 plug/socket at one end and an RJ11 plug at the other end.  There is
SL> nothing in the manual about optional line cords and the only mention of it 
SL> is to say that the modem's Austel permit is void if not used with this line
SL> cord.

Sounds like it's a mandatory component on that model.

SL> The plug/socket carries a similar warning in BIG black letters.

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

SL> Damn!  And I believed them...

It's (just) better than saying "you're too dumb to understand". 
(Has much the same nasty taste effect if you find out later, however.)


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?

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

SL> Well, at least that's been some help.

A pleasure.

Regards,
Dave Hatch.

--- Msgedsq 3.20