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-
-
- *******BIOC AGENT 003 COURSE IN********
- * *
- * ========================== *
- * =BASIC TELECOMMUNICATIONS= *
- * ========================== *
- * PART V *
- ***************************************
-
-
- PREFACE:
-
- PREVIOUS INSTALLMENTS OF THIS SERIES WERE FOCUSED ON TELEPHONY FROM A NETWORK
- POINT-OF-VIEW. PART V WILL DEAL WITH TELEPHONE ELECTRONICS FOCUSING
- PRIMARILY ON THE SUBSCRIBER'S TELEPHONE. HEREINAFTER SIMPLY REFERRED TO AS
- "FONE."
-
- WIRING:
- -------
-
- ASSUMING A STANDARD ONE-LINE FONE, THERE ARE USUALLY 4 WIRES THAT LEAD OUT OF
- THE FONE SET. THESE ARE STANDARDLY COLORED RED, CREEN, YELLOW, & BLACK. THE
- RED & GREEN SIRES 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. (SUCH AS RADIO SHACK'S
- OUTRAGEOUSLY PRICED 2 LINE & HOLD MODULE9.
-
- IN TELEPHONY, THE RED & GREEN WIRES ARE OFTEN REFERRED TO AS TIP (T) & RING
- (R). THE TIP IS USUALLY 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 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
- RECTIFIER BRIDGE WHICH COMPENSATES FOR POLARITY REVERSAL.] THIS I WHY UNDER
- CERTAIN (NON-DIGITAL) SWITCHILG 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 CURRENT (VDC) FLOWING THROUGH 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 13 VOLTS. THE RESISTANCE OF THE
- LOOP ALSO DROPS BELOW THE 2500 OHM LEVEL.
-
- AS OF NOW, YOU ARE PROBABLY SAYING TO YOURSELF THAT THIS IS ALL NICE AND
- TECHNICAL BUT WHAT THE HELL GOOD IS THE INFORMATION. WELL, ALSO CONSIDER
- THAT THIS VOLTAGE (& RESISTANCE) DROP IS HOW THE CO DETECTS THAT A FONE WAS
- TAKEN OFF HOOK (PICKED UP). IN THIS WAY, THEY KNOW WHEN TO START BILLING THE
- CALLING NUMBER. NOW WHAT DO YOU SUPPOSE WOULD HAPPEN IF A DEVICE SUCH AS A
- RESISTOR OR A ZENER DIODE WAS PLACED ON THE CALLED PARTIES LINE SO THAT THE
- VOLTAGE WOULD DROP JUST ENOUGH TO ALLOW TALKING BUT NOT ENOUGH TO START
- BILLING? FIRST OFF, THE CALLING PARTY WOULD NOT BE BILLED FOR THE CALL BUT
- CONVERSATION COULD BE PERSUED. SECONDLY, THE CO EQUIPMENT WOULD THINK THAT
- THE FONE JUST KEPT ON RINGING. THE TELCO CALLS THIS A "NO-NO" (TOLL FRAUD TO
- BE MORE SPECIFIC) WHILE PHONE PHREAKS AFFECTIONATELY CALL THIS MUTE A BLACK
- BOX.
-
- THE FOLLOWING ARE INSTRUCTIONS ON HOW TO BUILD A SIMPLE BLACK BOX. OF COURSE
- , ANYTHING THAT PREVENTS THE VOLTAE FROM DROPPING WOULD WORK.
-
- YOU ONE OR 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 THE 2 SCREWS ON THE NETWORK BOX LABELED >F<
- AND >RR<. WRAP THE RESISTOR BETWEEN THE 2 SCREWS MAKING SURE THAT IT DOESN'T
- TOUCH ANY OTHER TERMINALS!. NOW CONNECT ONE WIRE FROM THE SWITCH TO THE RR
- TERMINAL. FINALLY, ATTACH THE REMAINING WIRE TO THE GREEN 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 RINING (DO IT AGAIN IF IT
- DOESN'T) WITH OUT STARTING THE BILLING. IT IS IMPORTANT THAT YOU DO IT
- QUICKLY (LESS THAN ONE SECOND THEN PUT THE SWITCH IN THE FREE POSITION AND
- PICK UP THE FONE. KEEP ALL CALL SHORT AND PREFERRABLY UNDER 15 MINUTES.
-
- NOTE: IF ANYONE PICKS UP AN EXTENSION IN THE CALLED PARTIES HOUSE AND THAT
- FONE IS NOT SET FOR FREE THEN BILLING WILL START.
-
- NOTE #2: AN OLD WAY OF SIGNADLING 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).
-
- WARNING: 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!
-
- PICTORAL DIAGRAM:
- (STANDARD ROTARY K500 FONE)
-
- ---------------------------------------
- ! !
- ***BLUE WIRE**>>F< !
- ! * * !
- **WHITE WIRE** * !
- ! * !
- ! REISTOR !
- ! * !
- ! * !
- ! >RR<*******SWITCH**** !
- ! * !
- ****GREEN WIRE********************** !
- ! !
- ---------------------------------------
-
- NOTE: THE BLACK BOX WILL NOT WORK UNDER ESS OR OTHER SIMILAR DIGITAL
- SWITCHES SINCE ESS DOE 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 (RMS) OF
- AC CURRENT DOWN THE LINE (AT AROUND 15 TO 60 HZ) IN STANDARD FONES, THIS
- CAUES 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. A REGULAR 60
- WATT LIGHT BULB CAN ALSO BE HOOKED UP USING A SIMPLE (120 VAC) RELAY.
-
- WARNING: 90 & 120 VAC CAN GIVE QUITE A SHOCK. EXERCISE EXTREME CAUTION IF
- YOU WISH TO FURTHER PERSUE THESE TOPICS.
-
- ALSO INCLUDED IN THE RINGING CIRCUIT IS A CAPACITOR TO PREVENT THE DC CURRENT
- FROM INTERFERRING WITH THE BELL [A CAPACITOR WILL PASS AC CURRENT WHILE IT
- WILL PREVENT DC CURRENT FROM FLOWING (BY STORING IT)].
-
- ANOTHER REASON THAT THE TELCO HATES BLACK BOXES IS BECUASE RINGING USES ALOT
- OF COMMON-CONTROL EQUIPEMET, IN THE CO, WHICH USE ALOT OF ELECTRICITY. THUS
- THE RINGING GENERATORS ARE BEING TIED UP WHILE A FREE CALL IS BEING MADE.
- USUALLY CALLS THAT ARE ALLOWED TO RING FOR A LONG PERIOD OF TIME MAY BE
- CONSTRUED AS SUSPICIOUS. SOME OFFICES MAY BE SET UP TO DROP A TROUBLE CARD
- FOR LONG PERIODS OF RINGING THEN A "NO-NO" DETECTION DEVICE MAY BE PLACED ON
- THE LINE.
-
- INCIDENTALLY, THE TERM "RING TRIP" REFERS TO THE CO PROCESS INVOLVED TO STOP
- THE AC RINGING SIGNAL WHEN THE CALLING FONE GOES OFF HOOK.
-
- NOTE: 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.
- ] PHREAKING IS AN INTERACTIVE PROCESS NOT A PASSIVE ONE!
-
- 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
- (MAKING) THE LOCAL LOOP ONCE FOR EVERY DIGIT DIALED. SINCE THE PHYSICAL
- CONNECTION MUQT 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, THERE ARE 10 PULES PER SECOND (MAX). 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) BREAK PERIOD AND A 40 MS
- MAKE PERIOD. (60+40=100 MS = 1/10 MINUTE). THIS IS REFERRED TO AS A 60%
- BREAK INTERVAL. SOME OF THE MORE SOPHISTICATED ELECTRONIC FONES CAN SWITCH
- BETWEEN A 60% & A 67% BREAK INTERVAL. THIS IS DUE TO THE FACT THAT MANY
- FOREIGN NATIOS 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 DIALIN A FRIEND'S # OR SOMETHING ELSE.
- INCIDENTALLY, THIS METHOD WILL ALSO WORK WITH DTMF FONES SINCE ALL DTMF LINES
- CAN ALSO HANDLE ROTARY.
-
- ANOTHER PROBLEM WITH PULSE DIALING IS THAT IT PRODUCES HIGH-VOLTAGE SPIKES
- THAT MAKE LOUD NOISES IN THE EARPIECE AND CAUSE THE BELL TO "TINKLE." IF YOU
- NEVER NOTICED THIS THEN YOUR FONE HAS A SPECIAL "ANTI-TINKLE" & EARPIECE
- SHORTING CIRCUIT (MOST DO). IF YOU HAVE EVER DISSECTED A ROTARY FONE (A MUST
- FOR ANY SERIOUS PHREAK) YO WOULD HAVE NOTICED THAT THERE ARE 2 SETS OF
- CONTACT THAT OPEN AND CLOSE DURING PULSING (ON THE BACK OF THE ROTARY DIAL
- UNDER THE PLASTIC COVER). ONE OF THESE ACTUALLY OPENS AND CLOES THE LOOP
- WHILE THE OTHER MUTES THE EARPIECE BY SHORTING IT OUT. THE SECOND CONTACTS
- ALSO ACTIVATES A SPECIAL ANTI-TINKLE CIRCUIT THAT PUTS A 340 OHM RESISTOR
- ACROSS THE RINGING CIRCUIT WHICH PREVENTS THE HIGH VOLTAGE SPIKES FROM
- INTERFERRING WITH THE BELL.
-
- 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 UPTO 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 ANOTHGR 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 !
- ! ! ! 1 !
- !-----!-----!-----!-----1
- ! ! OPER! ! !
- 941 HZ-! * ! 0 ! # ! D !
- ! ! Z ! ! !
- !-----!-----!-----!-----!
- 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 O 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 AREA 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 AD 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) AD PLANS CAN BE FOUND IN TAP AS WELL AS ON MANY BBS'S.
-
-
- 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 CURRENT FLOWING 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.
-
- THE REASON 2 SIRES ARE USED ON THE LOCAL LOOPS ARE BECAUSE IT IS ALOT CHEAPER
- FOR THE TELCO. ALTHOUGH, ALL OF THE INTER-OFFICE TRUNKS UTILIZE 4 WIRES.
- THIS IS NECESSARY FOR FULL DUPLEX (IE, SIMULTANEOUS CONVERSATION ON BOTH
- SIDES) AND FOR AMPLIFICATION DEVICES. THERE ARE SIMILAR DEVICES IN THE CO'S,
- KNOWN AS A HYBRID, THAT COUPLE THE 4-WIRE TRUNKS TO THE 2-WIRE LOCAL LOOPS
- AND VISA-VERSA.
-
- 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 MST
- PUT A 1000 OHM RESISTOR (1 WATT) ACROS 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.
-
- *****BIOC
- *=$=*AGENT
- *****003
-
- This phile was passed through Damage, Inc.
-
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