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G8MNY  > TECH     26.06.19 08:45l 171 Lines 6816 Bytes #9 (0) @ WW
BID : 9880_GB7CIP
Subj: A Simple Telephone Tester
Path: ED1ZAC<ED1ZAC<F1OYP<VE2PKT<GB7CIP
Sent: 190626/0633Z @:GB7CIP.#32.GBR.EURO #:9880 [Caterham Surrey GBR] $:9880_GB
From: G8MNY@GB7CIP.#32.GBR.EURO
To  : TECH@WW

By G8MNY                                     (Updated Sep 15)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)

Ever needed to test the functions of a pair of Phones Answering machine, FAX,
Modem etc. without 2 telephone lines? This is a simple tester I knocked up in a
dual phone socket, plus a plug top PSU, to mimic most telephone line functions.


FEATURES

  PHONE 1 "off hook" can listen to dial tone
  Manual ringing of PHONE 2
  PHONE 2 "off hook" removes dial tone from PHONE 1
  PHONE 1 "on hook" causes line reversal to PHONE 2 (release the call test)
  Variable line loss
  Line status LED indicators


PLUG TOP PSU
                ÚÄÄÄÄÄÄÄÄ2k2ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ>Ringing drive
                ³
L¿ Ú¿    ÚÄÄÄÄÄÂÁÄ´>ÃÄÂÄÄÄÄÂÄÄÄÄÄÄÄÂÄÄÄÄÄ¿+60V
 ³ o )||(      ³      ³    ³      1k   ³/           4 way cable
 ³ | )||(      À´<ÃÄÄÄ)Ä¿  ³       ÃÄÄÄ´ T1
 ÀÄo )||( 36V         ³ ³ ===     _³_  ³\e
     )||(100mA Ú´>ÃÄÄÄÙ ³  ³470u  /_\'   ÀÄÄÄÄÄ>+50V (@ 40-80mA)
     )||(      ³        ³  ³100V   ³50V
NÄÄÄÙ    ÀÄÄÄÄÄÁÂÄ´<ÃÄÄÄÁÄÄÁÄÄÄÄÄÄÄÁÄÄÄÄÄÄÄÄÄÄÄ>0V
  heat fused    ³
  Transformer   ÀÄÄÄÄÄÄÄÄ´ÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ>Dial Tone
                         u1
                        100V

The 50V 1W zener is actually series of zeners, T1 is any 200mA 100V 2W NPN.

The transformer's AC voltage is not high enough to ringing a phone directly, so
it is used to drive a line reversing relay to make the ringing.

A small u1 capacitor takes off some of higher harmonics of the AC to mimic dial
tone.


TEST CIRCUIT

+50V>ÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄ¿
              _³_         ³                  ³     _³_
        LED 1=\_/         ³                  ³     \_/=LED 2
               ³         1k5                1k5     ³
Ringing>ÄÄÄÄÄo o         1W                 1W      ³
drive    RING / SW        ³                  ³   ___³___
          ___³___         ³                  ³  ³RELAY 2³
         ³RELAY 1³        ³                  ³   ~~~³~~~
          ~~~³~~~         ³                  ³      ³
         RING \ SW        ³                  ÃÄÄ2k2ÄÙ
             o oÄÄÄÄ2k2ÄÄÄ´     u47          ³
             ³            ³    100V    4k7   ³ relay 1
           ÚÄ)ÄÄÄÄÄÄÄÄÄÄÄÄÁÄ\ oÄ´ÃÄÄVARIABLEÄÁÄÂÄo  o¿
           ³ ³       relay 2 o      line loss  ³  \  ³
Calling 2<ÄÙ ³               ³                 ³   ÀÄ)ÄÄÄÂÄÄ>2
PHONE 1      ³  Dial tone>ÄÄÄÙ             ÚÄÄÄ)ÄÄÄÄÄÙ  ===     Answering
Socket  5<ÄÄÄ´                             ³   ³       1u³      PHONE 2
             ÃÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÁo  o      63vÀÄÄ>3  Socket
             ³                        relay 1\     
    0V>ÄÄÄÄÄÄÙ                                ÀÄÄÄÄÄÄÄÄÄÄÄÄÄ>5

Both relays are double changeover (only 1 needs to be) 28V 7mA DIL type, with
4k coil resistance, note some types may have internal diodes so polarity may
matter! During ringing RELAY 1 has to operate & release 50 time a seconds to
deliver +/- 50V to PHONE 2 to look similar to the 75V AC (17-25Hz) + 50V DC of
real telephone ringing.

The manual RING SWitch is a non locking double pole changeover.

Line loss & matching is all approximate, like the real world nothing is 600ohm!
But using 600 ohm test gear & blocking the DC etc. actual line losses could be
calibrated on the variable resistor scale (e.g. 10-30dB Max). A more realistic
dummy line & noise sources could be used as the middle section if it was
important (e.g. for a high speed modem evaluation).

      REAR VIEW LAYOUT
ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿
³      ()LED LED()        ³  The PCB is removed from the case by heating the
³ ÚÄ¿    2        1   ÚÄ¿ ³  melted spigots (with a soldering iron).
³ ³R³1u 1k5      1k5  ³R³ ³
³ ³L³            pot  ³L³ ³  The PCB needs links cutting to isolate the 2 lines
³ ³1³  4k7  u47       ³2³ ³  if it is a shared phone socket type. The PCB at
³ ÀÄÙ 1____6   1____6 ÀÄÙ ³  the switch location is cut away & it is mounted in
³o)  /______³ /______³  (o³  a drilled front case hole. Tight holes in the case
³     PHONE 2  PHONE 1    ³  are also made for the LEDs who's wires poke to new
³                         ³  PCB holes.
³  __                 []  ³
³ ³..³RING            []  ³  After testing reassemble & reheat anything left of
³ ³::³SW              []  ³  the spigots or use some glue.
³ ÀÄÄÙ                    ³
ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ

In UK jack pins 2 & 5 are the 2 wire line, & a 3rd (pin 3) wire may be used for
the phones ringer path capacitor normally in the master socket. See your local
telecomms Co. (POTS) arrangements if different from UK.


PHONE CALL SIMULATION

 1/ Connect 2 PHONE devices.

 2/ Lift PHONE 1, LED 1 lights up, listen to buzzing dial tone & U have "Blow".

 3/ Intermittently operate ringing switch (concadance ringing).

 4/ Does PHONE 2 ring? (LED 2 lights dimly to ringing) Can it answer the call?

 5/ On answer, LED 2 lights, PHONE 2 has "Blow", & PHONE 1 dial tone disappears
    & a transmission path to PHONE 2 is made.

 6/ Can you talk or send data both ways over transmission paths, is loss OK?

 7/ Clear down PHONE 2, LED 2 goes out, & dial tone is returned to PHONE 1.

 8/ If you cleared down PHONE 1 first instead, then PHONE 2 gets a line
    polarity reversals, which should cause automatic kit to hang up & clear the
    line for the next call. I found some kit just times out instead!


REAL PHONE TONES
 DTMF-Telephone Standards Touch-Tone dialing

 Touch-tone was a registered trademark of AT&T. It is also known as dual-tone
 multiple frequency (DTMF) signaling!

 The two tones in a 4 x 3 keypad matrix, a low-frequency tone & a high
 frequency tone, to specify 1 of the 16 options. Pressing 2 keys in the same
 row/column, normal results in a single tone. The 2 tones must not clip & mix
 as the DTMF Rx IC uses the presence of more than 2 tones the identify the
 signal non DTMF & ignores it.

 TONE HIGH 1209Hz 1336Hz 1477Hz (1633Hz)
  LOW
  697 Hz     1      2      3      (A)
  770 Hz     4      5      6      (B)
  852 Hz     7      8      9      (C)
  941 Hz     *      0      #      (D)

 Level each tone:               -6 to -4 dBm
 Maximum difference in levels:   4 dB
 Maximum level (pair):         + 2 dBm
 Frequency tolerance:          ñ 1.5%
 Pulse width:                    50 msec
 Time between digits:            45 msec minimum

 DIAL TONE: 350-440 Hz

 BUSY TONE: 480-620 Hz, with 60 interruptions per minute

 EQUIPMENT ENGAGED TONE: sounds like busy tone, but slightly different!

 RINGING TONE: 440-480 Hz, 2sec on, 4sec off

 RINGING VOLTAGE: 17-22Hz 75V AC to earth & -50V DC. (155V peak!)
     (cacadance)  Load AC 1000ohms via a 1.8/0.9uF.

 LINE CURRENT: Around 50mA, typically 10V across a phone in use.



Why Don't U send an Interesting Bul?

73 de John G8MNY @ GB7CIP


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