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From: ron@brl-tgr.ARPA (Ron Natalie )
Newsgroups: net.dcom
Subject: Re: RJ-41S and RJ-45S
Message-ID: <7475@brl-tgr.ARPA>
Date: Thu, 17-Jan-85 14:24:50 EST
Article-I.D.: brl-tgr.7475
Posted: Thu Jan 17 14:24:50 1985
Date-Received: Fri, 18-Jan-85 10:26:22 EST
References: <90@tove.UUCP>
Distribution: net
Organization: Ballistic Research Lab
Lines: 65

> 	"Connecting the modem to the telephone line with an RJ-11C jack
> 	is not recommended, although it may work under certain conditions.
> 	An RJ-11C voice jack requires a 4-wire telephone cable, not supplied 
> 	with the AJ-4048 modem."
> 

This is exactly true.  We hacked some eight wire->2 wire jobs on some other
modems, but they were only running at 1200 baud.  When AJ demonstrated
the modems they did exactly the same thing.

> I also think I am going to need to get myself a phoneset with an 8-wire 
> connector since the AJ doesn't autodial.  Are these available?
> 

No, you can mix a RJ-11 plug on the eight wire line just fine.

> My questions are:
> 	A. Is it likely to be a big deal or a little deal for the phone
> 	company to install that 8-wire jack in my house?  Are the 8 wires
> 	in the wall somewhere or does a major restringing occur?  (I would 
> 	guess from the descriptions of wires 7 and 8 below that they are
> 	just a volume control from the phone company built into the box.)
> 	B. Are there adaptors available to go from 8-wire to 4-wire connectors
> 	and back?  The quote above implies it is somehow possible.
> 	C. What is the real difference?  What are the circumstances under
> 	which RJ-11C will not work but RJ-41S will?
> 
There are still only two wires running to your house.  The jack is entirely
local to end of your two wires.

> Thanks for any and all help.
> By the way, the 8 wires are identified as follows (in the AJ manual):
> 
> 	1. no connection
> 	2. no connection
> 	3. Mode indicator.  Selects voice or data mode depending on state of
> 	   telset exclusion switch (or other control).
> 	4. Ring.  One side of telephone line.
> 	5. Tip.  Other side of telephone line.
> 	6. Mode Indicator Common.  Ground.
> 	7. Programming Resister.  Resistor (on data block) used to 
> 	   control modem transmit level.
> 	8. Programming resistor common.  Return side of PR signal (7. above).
> 
> 7 and 8 are identifed as: "Passive or isolated signal", and none of the
> rest are, whatever that means.

Ring and Tip are your two wires to the phone connector.

The Mode indicator and it's common are a signal as to wheter the modem
should connect itself to the line.  Even the RJ-11 vadic modems use that
feature.  You can either put a little toggle switch on the extra two wires
of the RJ-11C, or disable the feature entirely by using the little adapter
that VADIC gives you which does nothing but disconnect these two wires.
This is usually used by the use of an Exclusion key (that's that funny
white plunger on the handset, or the little clear twist knob on the top
of the dial).

The programming resistor is a resistor.  It's value is set up by the phone
company to give you an idea what the loss of your loop to the central office
is.  I suppose you can just do this by trial and error.  Anyway, AJ demonstrated
the 4800 baud modems here just by connecting them to an RJ11 so their disclaimer
is probably just CYA stuff.

-Ron