G'day Dave!



 -=> In a message on 28 Jan 96 <=-

 -=> Dave Hatch said this to Stephen Lennie <=-



 SL> NetComm SmartModems use a telephone cord with a piggy-back type plug on

 SL> the end which seems to perform exactly the same as a standard (MODE 1)

 SL> double adaptor except that it has, what appears to be, a capacitor

 SL> between pins 2 and 6.

 

 SL> > AUSTEL PERMIT NO: A90/831/0179



 DH> 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]



 DH> Is this cable permanently attached to the modem, or connected via a RJ

 DH> plug and socket? 



No, not permanent.  Yes, connected via 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.



 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. 



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



 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. 



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



I've noticed that many modern phones can be set to either NORM (normal) or

600 Ohms and this is supposed to affect the sidetone, but I've only seen

references to the 600 Ohm resistance when connected to *some* PABXs.



If I toggle this switch on my phone the sidetone is slightly louder and

slightly higher pitched, but no great difference.



 DH> Does the manual detail the operational requirement for when to, and

 DH> when not to, use this attachment?  (It should.) 



The cable originally came with my NetComm M7F but I continued to use it with

my M34F because it has the piggy-back plug - very handy.  NetComm say that it

doesn't matter what (recent) model of NetComm modem I use the line cord with.



The cable came with the M7F as the standard telephone line cord, with a

605/610 plug/socket at one end and an RJ11 plug at the other end.  There is

nothing in the manual about optional line cords and the only mention of it is

to say that the modem's Austel permit is void if not used with this line cord.



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. 



Damn!  And I believed them...



 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. 



Well, at least that's been some help.





BFN

  _

 (_`

 ._)teve







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 # Origin: Stephen S. Lennie, Fingerprint: 4250455723F5E09A-DDE7CB9FB43FAE20



... Off-topic, yes, but useless knowledge should not be wasted...

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