                       CHAPTER FIVE: YOUR FONE

     Previous chapters of this course were focused on telephony from 
a Network point-of-view.  Chapter Five will deal with telephone 
electronics focusing primarily on the subscriber's telephone.  
Hereinafter simply referred to as "fone."  Here will also be 
presented the plans for a Black Box and a White Box and a hold 
device, and the description of a Silver Box.


Wiring:
-------
     Assuming a standard one-line fone, there are usually 4 wires 
that lead out of the fone set.  These are standardly colored red, 
green, yellow, & black.  The red & green wires are the two that are 
actually hooked up to your CO.  The yellow wire is sometimes used to 
ring different fones on a party line (ie, one #, several families--
found primarily in rural areas where they pay less for the service 
and they don't use the fone as much); otherwise, the yellow is 
usually just ignored. 
     On some two-line fones, the red & green wires are used for the 
first fone # and the yellow & black are used for the second line.  In 
this case there must be an internal or external device that switches 
between the two lines and provides a hold function. 
     In telephony, the green & red wires are often referred to as tip 
(T) & ring (R), respectively.  The tip is the more positive of the 
two wires.  This naming goes back to the old operator cord boards 
where one of the wires was the tip of the plug and the other was the 
ring (of the barrel).
     A rotary fone (aka dial or pulse) will work fine regardless of 
whether the red (or green) wire is connected the tip(+) or ring(-).  
A touch-tone (TM) fone is a different story, though.  It will not 
work except if the tip(+) is the green wire. [Although, some of the 
more expensive DTMF fones do have a bridge rectifier which 
compensates for polarity reversal.]  This is why under certain (non-
digital) switching equipment you can reverse the red & green wires on 
a touch-tone fone and receive free DTMF service.  Even though it 
won't break dial tone, reversing the wires on a rotary line on a 
digital switch will cause the tones to be generarted.

Voltages, Etc.
--------------
     When your telephone is on-hook (ie, hung up) there is 
approximately 48 volts of DC potential across the tip & ring.  When 
the handset of a fone is lifted a few switches close which cause a 
loop to be connected (known as the "local loop") between your fone & 
the CO.  Once this happens DC current is able to flow through the 
fone with less resistance.  This causes a relay to energize which 
causes other CO equipment to realize that you want service.  
Eventually, you should end up with a dial tone.  This also causes the 
48 VDC to drop down into the vicinity of 12 volts.  The resistance of 
the loop also drops below the 2500 ohm level, though FCC licensed 
telephone equipment must have an off-hook impedance of 600 ohms.
     Because of this, you can talk without your fone ever knowing you 
answered.  Something that keeps the voltage up after you lift the 
receiver lets you talk, and the fone company thinks it is still 
rining, so no one is billed.  This device is a black box.



                              BLACK BOX
                              ---------

     The following are instructions on how to build a simple black 
box.  Of course, anything that prevents the voltage from dropping 
would work.  A black box is a device the is hooked up to your 
telephone that fixes the phone so that when you get a call, the 
caller doesn't get charged for the call.  This is good for calls up 
to 1/2 hour, after which the Telephone Company starts to get 
suspicious.
     What this little beauty does is keep the line voltage from 
dropping to 10V when you answer the phone.  The line is kept at 36V 
and it will make the phone think it is still ringing while you are 
talking.  The reason for the 1/2 hour time limit is that the
Telephone Company thinks that something is wrong after 1/2 hour of 
ringing.
     You only need two parts:  A SPST toggle switch and a 10,000 ohm 
(10 K), 1/2 watt resistor.  Any electronics store should stock these 
parts.  Now, cut 2 pieces of wire (about 6 inches long) and attach 
one end of each wire to one of the terminals on the switch.  Now turn 
your K500 (standard desk fone) upside down and take off the cover.  
Locate wire (disconnect it from its terminal).  Now bring the switch 
out the rear of the fone and replace the cover.
     Put the switch in a position where you receive a dial tone.  
Mark this position NORMAL.  Mark the other side FREE.  When your 
phriends call (at a prearranged time), quickly lift & drop the 
receiver as fast a possible.  This will stop the ringing (do it again 
if it doesn't) with out starting the billing.  It is important that 
you do it quickly (less than 1 second). Then put the switch in the 
FREE position and pick up the fone. 
     All of the parts are available at your friendly neighborhood 
Radio Shck.  Using the least possible parts and arrangement, the cost 
is only 98 cents!  And that is parts for two of them.  If you want to 
splurge you can get a small PC board, and a switch.  
     The purpose of this box is to let phriends call without having 
to pay.  Because it is made to receive calls, while the box is on, 
you cannot call out.  When the box is on you may receive calls.  The 
phone will ring like normal, and the LED on the box will flash.  If 
you answer, the LED will light and the caller will not be charged.
     Hang up after you are done like normal.  You will not be able to 
get a dial tone or call out, so turn the box off for normal calls.  I 
do not recommend you leave the box on all the time, as you don't want 
it answering when Ma Bell calls!

WARNING:
     If someone picks up an extension in the called parties house and 
that fone is not set for FREE then billing will start.  The Telco can 
detect black boxes if they suspect one on your line.  This is done 
due to the presence of AC voice signal at the wrong DC level!

NOTE:
     An old way of signalling a phriend that you are about to call is 
making a collect call to a non-existant person in the house.  Since 
your friend will not accept the charges, he will know that you are 
about to call and thus prepare the black box (or visa versa).
Pictoral Diagram:  There are two schematics for this box.  One is for 
normal phones, the second is for phones that don't work with the 
first kind.  


                     SCHEMATIC 1 FOR MOST FONES 

Parts:
                         FROM   >--------------------GREEN->    TO
1 1.8K 1/2 watt          LINE   >--+   1.8K  LED  +---RED-->   FONE
  resistor                         +--/\/\/\--|>--+
1 1.5V LED                         |              |
1 SPST switch                      +----->/<------+
                                         SPST

                      SCHEMATIC 2 FOR ALL FONES  

                         FROM   >---------------GREEN->    TO
                         LINE   >------+      +--RED-->   FONE
Same parts as last                     |  LED |
     scheme.                           +->/<--+>-+
                                       |         |
                                       +--/\/\/--+
                                           1.8K


NOTE:
     The Black Box will not work under ESS or other similar digital 
switches since ESS does not connect the voice circuits until the fone 
is picked up (& billing starts).  Instead, ESS uses an "artificial" 
computer generated ring.

Ringing:
--------
     To inform a subscriber of an incoming call, the Telco sends 90 
volts (PK) of pulsing DC down the line (at around 15 to 60 Hz; 
usually 20 Hz).  In most fones this causes a metal armature to be 
attracted alternately between two electro-magnets thus striking 2 
bells.  Of course, the standard bell (patented in 1878 by Tom A. 
Watson) can be replaced by a more modern electronic bell or signaling 
device.
     Also, you can have lights and other similar devices in lieu of 
(or in conjunction with) the bell.  A simple neon light (with its 
corresponding resistor) can simply be connected between the red & 
green wires (usually L1 & L2 on the network box) so that it lights up 
on incoming calls.
     Incidentally, the term "ring trip" refers to the CO process 
involved to stop the AC ringing signal when the calling fone goes off 
hook.  It is suggested that you actually dissect fones to help you 
better understand them.  It will also help you to better understand 
the concepts here if you actually prove them to yourself.  For 
example, actually take the voltage readings on your fone line [any 
simple multi-tester (a must) will do.]



Dialing:
--------
     On a standard fone, there are two common types of dialing:  
pulse & DTMF.  Of course, some people insist upon being different and 
don't use the DT thus leaving them with MF (Multi Frequncy, aka 
operator, blue box) tones.  This is another "no-no" and the Telco 
Security gentelmen have a special knack for dealing with such 
"phreaks" on the network.
     When you dial rotary, you are actually rapidly breaking & 
reconnecting (breaking & making) the local loop once for each digit 
dialed. Since the physical connection must be broken, you cannot dial 
if another extension (of that #) is off-hook.  Neither of the fones 
will be able to dial pulse unless the other hangs up.
     Another term often referred to in telephone electronics is the 
break ratio.  In the US, the standard is 10 pulses per second.  When 
the circuit is opened it is called the break interval.  When it is 
closed it is called the make interval.  In the US, there is a 60 
millisecond (ms) make period and a 40 ms break period.  (60+40=100 ms 
= 1/10 second).  This is referred to as a 60% make interval.  Some of 
the more sophisticated electronic fones can switch between a 60% & a 
67% make interval.  This is due to the fact that many foreign nations 
use a 67% break interval.
     Have you ever been in an office or a similar facility and saw a 
fone waiting to be used for a free call but some asshole put a lock 
on it to prevent outgoing calls?
     Well, don't fret phellow phreaks, you can simulate pulse dialing 
by rapidly depressing the switchook.  (If you depress it for longer 
than a second it will be construed as a disconnect.)  By rapidly 
switchooking you are causing the local loop to be broken & made 
similar to rotary dialing!  Thus if you can manage to switchook 
rapidly 10 times you can reach an operator to place any call you 
want!  This takes alot of practice, though.  You might want to 
practice on your own fone dialing a friend's # or something else.  
Incidentally, this method will also work with DTMF fones since all 
DTMF lines can also handle rotary.
     Dual Tone Multi Frequency (DTMF) is a modern day improvement on 
pulse dialing in several ways.  First of all, it is more convenient 
for the user since it is faster and can be used for signaling after 
the call is completed (ie, SCC's, computers, etc.).  Also, it is more 
up to par with modern day switching equipment (such as ESS) since 
pulse dialing was designed to actually move relays by the number of 
digits dialed (in SxS offices).
     Each key on a DTMF keypad produces 2 frequencies simultaneously 
(one from the high group and another from the low group).

          -------------------------
Low Group |  Q  | ABC | DEF |     |
   697 Hz-|  1  |  2  |  3  |  A  |
          |-----|-----|-----|-----|
          | GHI | JKL | MNO |     |
   770 Hz-|  4  |  5  |  6  |  B  |
          |-----|-----|-----|-----|
          | PRS | TUV | WXY |     |
   852 Hz-|  7  |  8  |  9  |  C  |
          |-----|-----|-----|-----|
          |     | OPER|     |     |
   941 Hz-|  *  |  0  |  #  |  D  |
          |-----|-----|-----|-----|
           1209  1336  1477  1633
             (High Group--in Hz)

     A portable DTMF keypad is known as a white box.  The fourth 
column (1633 Hz) is not normally found on regular fones but it does 
have several special uses.  For one, it is used to designate the 
priority of calls on AUTOVON, the military fone network.  These key 
are called:  Flash, Immediate, Priority, & Routine (with variations) 
instead of ABCD.  Secondly, these keys are used for testing purposes 
by the Telco.  In some areas you can find loops as well as other neat 
tests (see Part II) on the 555-1212 directory assistance exchange.  
For this, you would call up an DA in certain areas [that have an 
Automatic Call Distributor (ACD)] and hold down the "D" key which 
should blow the operator off.  You will then hear a pulsing dial tone 
which indicates that you are in the ACD internal testing mode.  You 
can get on one side of a loop by dialing a 6.  The other side is 7.  
Some phreaks claim that if the person on side 6 hangs up, 
occasionally the equipment will screw up and start directing 
directory assistance calls to the other side of the loop.  Another 
alleged test is called REMOB which allows you to tap into lines by 
entering a special code followed by the 7 digit number you want to 
monitor.  Then there is the possibility of mass conferencing.
     ACD's are become rare though.  You will probably have to make 
several NPA-555-1212 calls before you find one.  You can modify 
regular fones quite readily so that they have a switch to change 
between the 3rd and 4th columns.  This is called a silver box (aka 
grey box).

Transmitter/Receiver:
---------------------
     When you talk into the transmitter, the sound waves from your 
voice cause a diaphragm to vibrate and press against the carbon 
granules (or another similar substance).  This causes the carbon 
granules to compress and contract thus changing the resistance of the 
DC coupled path through it.  Therefore, your AC voice signal is 
superimposed over the DC current of the local loop.  The receiver 
works in a similar fashion where the simple types utilize a magnet, 
armature, & diaphragm.

Hybrid/Induction Coil:
----------------------
     As you may have noticed, there are two wires for the receiver 
and two for the transmitter in the fone, yet the local loop consists 
of 2 wires instead of 4.  This 4-wire to 2-wire conversion is done 
inside the fone by a device known as an induction coil which uses 
coupling transformers.  All of the internal Telco trunks also use 4 
wires.  It is only the local loop that uses 2 since it is cheaper.  A 
device in the CO known as a hybrid converts between 4 and 2 wire set-
ups similar to the induction coil inside the fone.  Special data 
transmission lines require extremely low signal to noise ratios, they 
require the full four wires--two for transmission and two for 
receiving (even on the local loop).

Miscellaneous:
--------------
     In the telephone, there is also a balancing network consisting 
of a few capacitors & resistors which provide sidetone.  Sidetone 
allows the caller to hear his own volume in the receiver.  He can 
then adjust his voice accordingly.  This prevents people from 
shouting or speaking too softly without noticing it.

Hold:
-----
     When a telephone goes off hook, the resistance drops below 2500 
ohms.  At this point, the Telco will send a dial tone.  To put 
someone on hold you must put a 1000 ohm resistor (1 watt) across the 
Tip & Ring before it reaches the switchook.  In this way, when the 
fone is hung up (for hold) the resistance remains below 2500 ohms 
which causes the CO to believe that you are still off-hook.  You can 
build a simple hold device using the following pictoral diagram:

                                     /
    (RED) O-------------------------+
    [L1]       |             |      |
               |             |      |
           1000 Ohm          |      |
           Resistor       Ringing   |
               |          Circuit   |
               |             |      |
               /             |  Switch-
              / SPST Switch  |   Hook
               |             |      |
               |             |      |
               |             |      |/
   (GREEN) O---+-------------+------/
    [L2]
                      --> To Rest of
                             Fone

     This hold device is only effective if you also hang up the fone.  
To make a hold/mute switch, simple connect a wire in place of the 1K 
resistor to effect a short circuit (who cares if you damage CO 
equipment?).
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