Index Home About Blog
From: Julian Macassey <julian@bongo.uucp>
Subject: Re: FCC REN Numbers (Was: BT Phones, etc)
Date: 22 May 90 15:16:11 GMT
Organization: The Hole in the Wall  Hollywood California U.S.A.

In article <>, mtndew! writes:

> Julian Macassey writes about RENs (Ringer Equivalence Numbers),
> quoting chapter and verse from FCC part 68 rules.  This comes at a
> fortuitous time because I was just wondering about it myself.

> Why do the RENs vary?  I have noticed quite a wide range of ringer
> equivalences, and while thinking about this I came up with a bunch of
> statements that a telephone designer might make about them.  Which of
> these are true or likely and which are false?

	RENs vary because different designs of ringers consume
different amounts of power. The same reason Horse Power varies.

> 	"physical bells take 1.0 REN, that's just the way it is"
	Physical Bells, or gong ringers as they are known take an REN
(Ringer Equivalence Number) of 1.0 A because they are the standard by
which other devices are measured. The classic gong ringer in Western
Electric telephone is the standard ringer. I have seen Korean
telephones with gong ringers rated at 3.0 A. Yup, two of those phones
on the same line would not ring.

> 	"it's harder to make the ringer circuit with lower RENs"

	It's very easy, but seeing as the REN is an indication of
power consumption, a low REN ringer may not be heard. The purpose of
ringers is to be heard. The most efficient ringer, if hearing and
directionality is important, is the classic gong ringer (REN 1.0 A).
Modems, phone answering machines etc, often have an REN of 0.0. They
just need to sniff the AC voltage to then get the logic to grab the
line etc. Yes, you could make a REN 0.0 device that would power a
steam whistle. But most of the world's ringers are self powered.

> 	"lower REN is better because you can get more instruments
> 	 on a line"

	Yes, this is true. The telco claims that they can ring a total
REN of 5.0. So you could have ten 0.5 REN phones on line.

> 	"we didn't really think about the REN when we built the
> 	 phone, that's just what it ended up being"
	This is partially true. The power consumed by the ringer has
always been important. In the old days, the company that built the
ringers also built the ring generators, so they were matched. When
subscriber equipment was deregulated, the FCC and Ma Bell came up with
the REN to enable ringers to be measured. I am sure that to this day
that AT&T have massive docs describing ringers and ring generators.

> 	"the phone switch likes higher REN phones better"

	Nope, Higher REN phones consume more power. The telco worries
that you are using their power. I had a hilarious meeting with AT&T
dweebs once about on-hook power consumption and what it would cost
them in extra batteries if every subscriber took 1 Ma while on hook to
run dialer memories etc. If your phone has an REN of 0.2, they are
quite happy.

> 	"we always built phones with REN=xx and saw no reason to change"

	Nope, They built standard electro-mechanically resonant gong
ringers because they gave the highest SPL per Watt. To this day, their
is not a better ringer known to me than a classic AT&T double gong
ringer.  They are not cheap, electronic ringers are much cheaper.

> 	"if the REN is too low, it will trigger sporadically (say,
> 	 via pulse dialing on another extension"

	If the REN is too low, nothing will happen, except it will
consume less power. The REN can be 0.0, look at your modem. The
sporadic triggering you talk of, called "bell tap" in the trade, is
causeed by poorly designed ringers of any REN. The 3.0 REN monster I
mentioned above bell tapped.

> 	"off-the-shelf phone line interfaces have REN=xx so that's
> 	 why we used it".

	I don't understand this statement. 

> Should one even bother to look at the REN when buying a phone?

	Yes, if you have more than one instrument on a line, it is
important.  If the Telco will ring ringers up to a total of 5 REN and
you add another instrument bringing your REN to or above the limit,
several things may happen:

	All the bells will stop ringing. Some of the bells will stop
ringing.  Some will stop and others will be weak. They will all be

Julian Macassey, n6are  ucla-an!denwa!bongo!julian
N6ARE@K6IYK (Packet Radio) [] voice (213) 653-4495

From: Julian Macassey <julian@bongo.uucp>
Subject: Re: FCC REN Numbers
Date: 26 May 90 01:41:14 GMT
Organization: The Hole in the Wall  Hollywood California U.S.A.

In article <>, (David
Tamkin) writes:

> In volume 10, issue 377, Julian Macassey answered some of Steve
> Friedl's questions about FCC ringer equivalence numbers.
> I have three far simpler ones (I guess):

> 1. What does the B or A after an REN mean?

	I think I covered this in an earlier posting, but then I could
have glossed over it. The letter at the end of the REN numbers covers
the "Ringing type" from the notorious Table I. A Ringing type A ringer
is sensitive to 20 Hz +-3 and 30 Hz +-3. A B type ringer is sensitive
to AC voltage between 15.3 and 68.0 Hz. Just for the curious, a C type
ringer is sensitive between 15.3 and 17.4 Hz. There are many classes
of ringers. I know that the class is supposed to refer to the
frequency coverage, but owing to obscurity in the FCC regs, some labs
measure type B ringers (Electronic warble type) as a type A so they
can get a lower REN. 

This does not make it a type A ringer. This makes it a type B ringer
measured as a type B. Apart from type B, other ringers cover a narrow
frequency range. This frequency selectivity is sometimes used with
party lines. It is also one of the factors that limits bell tap in US
phones. See an earlier posting of mine where I waffle about this. Yes,
most Type B ringers will also respond to frequencies above 68 Hz, like
100 Hz.

> 2. If the ringer on a telephone can be turned off, does it no longer
> count in figuring the total REN load on a line?

 	I wish this was true. If you look carefully, you will notice
that only the output transducer (fancy name for gong, Loudspeaker or
piezo disc) is disconnected, but that the power consuming stuff is
still on line. In a gong ringer the "off button" is often an arm that
obstructs the striker, so no power is saved by turning it off. With
electronic ringers, depending on the design, some power may be saved.
I have quietly campaigned to have the off switch disconnect the ringer
from the line. It does not disconnect the ringer because, it always
used to be that way. But that was then when there was maybe only one
instrument on the line. These days, you may want the ringer off,
because you have too many on line. To take a ringer off line you have
to actually disconnect it internally.
In the old days, the gong ringer circuit was left in circuit at all
times so the telco could sling an AC test circuit down the line at the
dead of night and the ringer provided a return path. Note recent
postings about strange telephone modems etc going chirp in the night.
They also had records of your normal impedance, so any change could
tell them if water was seeping into the line etc. It also told them
that you had bootlegged a phone on the line. They then got snotty.
Most techie types then learned to disconnect the ringer on any
bootlegged phones. Now many residential lines have tons of ringers on
them and they change continually - must drive the test board guys nuts
 - any comments from CO types? Most electronic ringers do not provide
a good profile to telco test circuits, the exception I know about is
the Motorola ringer IC. Motorola does it with a chain of Zeners.

	So one other point, the "low" or "medium" switch on most
electronic ringers is in fact a resistor switched between the ringer
IC and the transducer, so the volume is low, but the power consumption
is often just as high. My ideal electronic ringer would have the low
switch put the resistor on the line before the ringer IC and the off
switch would remove the whole circuit from the line. Yes, I know that
if the "low" resistor is before the IC, it will make the circuit
touchy in the low mode, depending on available power it would either
make no difference in volume or silence the bugger entirely.

> 3. Two of my modems *do* have REN's, though neither has any sort of
> bell or gong.  They check in at "0.4 1.2B" and "0.5A 1.6B"
> respectively.  My other modem has a speaker and thus does make a noise
> (but the speaker is powered by the electric utility, not the telco);
> it has an FCC ID but no REN on it at all.

	If the REN is below a 0.1 REN, it can be listed as 0.0 or
nothing at all put on the label. See above for dreary details on the
funny A and B numbers. In truth, all modems I have seen are type B
ringers. To prove this, feed say 60V at 60 Hz (yes power via a regular
transformer) to a modem, betya it picks up if in answer mode.

	I wrote extensively about all this ringer stuff years ago in
Popular Communications mag, but I suppose it wasn't all that popular
then.  Plus of course the editors used to bugger and censor my text so
some of the more esoteric stuff was jumbled and meaningless by the
time it reached the public and vulgar gaze.

Julian Macassey, n6are  ucla-an!denwa!bongo!julian
N6ARE@K6IYK (Packet Radio) [] voice (213) 653-4495

Date: Tue, 30 Jun 92 01:48 PDT
From: (John Higdon)
Reply-To: John Higdon <>
Organization: Green Hills and Cows
Subject: Re: Ringer Equivalency Numbers (Julian Macassey) writes:

> The Telco guarantee to ring a total of 5.0 REN. If you have an
> REN of 7.4 ringing, it indicates that either the numbers are untrue
> (possible) or you are near the CO (most likely).

Also, if you are exceeding 5.0 REN watch out for a characteristic of
some offices (notably the 1/1AESS equipped ones). What these switches
do for a self-protection measure is to simply shut off ringing current
to the over-RENed line. The caller gets ringback as usual, but nothing
makes a peep at the called end.

Years (and years) ago, before my PBX-in-home days, I used to have all
kinds of things hanging on the line such as dialers, weird bedside
clock radio phones (with RENs like 1.75), and other gadgets. One day
someone asked where I had been all day since I did not answer the
phone. Upon checking, I discovered that no ring voltage was being
delivered during a call. A call to 611 brought a repairman to the door
who informed me that they "saw" a lot of ringers on the line and if I
took some of them off, things would start working again.

They did.

        John Higdon         |   P. O. Box 7648   |   +1 408 264 4115      | San Jose, CA 95150 |       M o o !

Index Home About Blog