The Hacker's Encyclopedia 1998/hackers_encyclopedia.iso/phreak/sysinfo/fonpatch.txt

Text File | 2003-06-11 | 28.8 KB | 607 lines

>------cut, slash, deforest ----------------------
>
>                BUILDING AND USING PHONE PATCHES
>
>     From simple to elegant, patches help make the connection
>
>
>                               By
>
>                     Julian Macassey, N6ARE
>


>              First Published in Ham Radio Magazine
>                          October 1985.
>
>
>     In  telephone  company parlance, a patch is  any  connection
>between  a phone line and another communications device,  whether
>it be a radio, a tape recorder, a data device (such as a  modem),
>or even another phone line.
>
>     Radio Amateurs, on the other hand, tend to limit the meaning
>of "patch" to the connection of transmitters or receivers to  the
>phone  line  for phone conversations.  But there's more to  it  -
>Amateurs  can  and do use phone patches for purposes  other  than
>telephone conversations.  One particularly effective  application
>is   for  checking  TVI  and  RFI  complaints;  simply  set   the
>transmitter on VOX, go to the site of the interference complaint,
>and  then  key your transmitter via the phone line.   Doing  this
>will indicate whether your transmitter is or is not the source of
>the  problem.   If  it is, you can use this method  to  test  the
>measures you've taken to correct the problem.
>
>     A  phone line is, simply speaking, a 600-ohm  balanced  feed
>device  - which also happens to be how professional audio can  be
>described.    Most  modern  Amateur  transmitters  have   600-ohm
>unbalanced  inputs;  most  cassette  recorders  have  a   600-Ohm
>unbalanced  input;  the "tape" outputs on home stereos  are  also
>600-ohm  unbalanced.  All this makes patching relatively  simple.
>While there are various degrees of sophistication and  complexity
>in patching, in an emergency, patches can be easily put  together
>using  readily available components.  Before starting to build  a
>patch, however, it might be helpful to read last month's  article
>on understanding phone lines.
>
>
>The Simple Patch
>
>     The  simplest way to patch a phone line to another piece  of
>equipment  is  to use a couple of capacitors to block  the  phone
>line  DC.   While this simple approach will work in a  pinch,  it
>will  tend to introduce hum to the line because of the  unbalance
>introduced.  The capacitors used should be nonpolar, at least  2-
>ohm F, and rated at 250 volts or better (see fig.1).
>
>     To  hold  the line, the patch should provide a  DC  load  by
>means  of  a resistor (R6) or by simply leaving a phone  off  the
>hook.  The receiver output may need a DC load (R7) to prevent the
>output stage from "motorboating."  Use two capacitors to maintain
>the balance.
>
>     With all patches hum can be lessened by reversing the  phone
>wires.  A well-made patch will have no discernible hum.
>
>
>The Basic Phone Patch
>
>     Because  a phone line is balanced and carries DC as well  as
>an  AC signal, a patch should include a DC block, a balun, and  a
>DC load to hold the line.  The best component for doing this is a
>600-ohm 1:1 transformer such as those used in professional  audio
>and for coupling modem signals to the phone line, available  from
>most electronics supply houses.  Old telephone answering machines
>are   also   a  good  source  of  600-ohm   transformers.    Some
>transformers are rated at 600-900 ohms or 900-900 ohms; these are
>also  acceptable.   Make sure that the transformer  has  a  large
>enough  core,  because  DC current will be  flowing  through  it.
>(Some  small-core transformers become saturated and  distort  the
>signal.)
>
>     In section 68.304 of the FCC Part 68 regulations, it  states
>that  a coupling transformer should withstand a 60 Hz 1kV  signal
>for one minute with less than 10 mA leakage.  For casual use this
>may seem unimportant, but it provides good protection against any
>destructive  high voltage that may come down the phone line,  and
>into  the  Amateur's equipment.  A 130 to 250  volt  Metal  Oxide
>Varistor  (MOV)  across  the  phone  line  will  provide  further
>protection if needed.
>
>     The  DC resistance of the transformer winding may be so  low
>that  it hogs most of the phone line current.   Therefore,  while
>using  a phone in parallel for monitoring and dialing - which  is
>recommended  -  the audio level on the incoming line may  be  too
>low.   Resistors  R1A  and R1B (see fig.2) will  act  as  current
>limiters  and allow the DC to flow through the phone  where  it's
>needed.    If   possible,  these  resistors  should   be   carbon
>composition types.
>
>     To  keep  the line balanced, use two resistors of  the  same
>value  and adjust the values by listening to the dial tone  on  a
>telephone  handset.  There should be little or no drop in  volume
>when the patch transformer is switched across the phone line.
>
>     One  of these transformers, or even two capacitors,  can  be
>used to patch two phone lines together, should there be a need to
>allow  two  distant parties to converse.  There  will  be  losses
>through the transformer so the audio level will degrade, but with
>two good connections this will not be a problem.
>
>     On the other side of the transformer - which could be called
>the  secondary winding - choose one pin as the ground and  attach
>the shields of the microphone and headphone cables to it.  Attach
>the inner conductors to the other pin.  The receiver output  will
>work  well into the 600-ohm winding, and if transmitting  simplex
>or  just  putting  receiver audio on the line there  will  be  no
>crosstalk  or  feedback  problems.   In  some  cases,  the  audio
>amplifier  in a receiver does not have enough output to feed  the
>phone line at an adequate level; this can be handled by using the
>transformer with two secondaries (see the "improved" patch below)
>or by coupling a 8:1 kilohm transformer between the audio  output
>and  600-ohm transformer.  If RF is getting into the  transmitter
>input, a capacitor (C1) across the secondary should help.  A good
>value  for the lower bands and AM broadcast interference  is  0.1
>uF.   For  higher frequencies, 0.01 uF usually gets  rid  of  the
>problem.  Unshielded transformers are sensitive to hum fields and
>building  any patch into a steel box will help alleviate  hum  as
>well as RFI.
>
>
>The Improved Phone Patch
>
>     Several enhancements can be made to the basic phone patch to
>improve  operation.  The first is the addition of  a  double-pole
>double-throw switch to reverse the polarity of the phone line  to
>reduce  hum.  This may not be necessary with a patch at the  same
>location  with the same equipment, but if it is, experiment  with
>the  polarity of the transformer connections and adjust  for  the
>least  hum.   Most of the time the balance will be so  good  that
>switching  line polarity makes no difference.  The switch  should
>have a center "off" position or use a separate double-pole single
>throw switch to disconnect from the line.  The two secondaries on
>the  "improved"  patch (fig.3) should be checked for  balance  by
>connecting  the  receiver and transmitter and  checking  for  hum
>while  transmitting and receiving.  Switch the shield  and  inner
>conductors of the secondaries for minimum hum.
>
>     Many transmitters do not offer easy access to the microphone
>gain control.  There may also be too much level from the patch to
>make  adjustment of the transmit level easy.  Placing R10  across
>the  transformer allows easy adjustment of the level.  It can  be
>set  so  that when switching from the station microphone  to  the
>patch the transmitter microphone gain control does not need to be
>adjusted.   This  will  also  work  on  the  basic  600-ohm   1:1
>transformer.   Most  of  the  time a  1  kilohm  potentiometer  -
>logarithmic  if  possible  - will work well.  If  not,  a  linear
>potentiometer  will  do. A 2.5kilohm  potentiometer  may  provide
>better control.
>
>
>Deluxe Operation and VOX
>
>     Using  VOX  with  a phone patch may  cause  a  problem  with
>receive  audio going down the line and into the  transmit  input,
>triggering the VOX.  There may not be enough Anti-VOX  adjustment
>to  compensate for this.  The usual solution for this problem  is
>to use a hybrid transformer, a special telephone transformer with
>a phasing network to null out the transmit audio and keep it  off
>the  receive line.  Most telephones employ a similar  transformer
>and circuit so that callers will not deafen themselves with their
>own voices.  These devices are called "networks" (see figs. 4 and
>5).
>
>     A network can be removed from an old phone and modified into

>a  deluxe patch, or the phone can be left intact and  connections
>made  to  the line and handset cords.  The line  cord  should  be
>coupled to a 600-ohm 1:1 transformer  to keep the ground off  the
>line.   Note,  in the network schematics, that the  receiver  and
>transmitter  have a common connection; when coupling into  radios
>or other unbalanced devices, make this the ground connection.
>
>     There may be confusion about terms used in the network.  The
>telephone  receiver  is receiving the phone line audio,  and  the
>transmitter is transmitting the caller's voice.  For phone  patch
>use,  a telephone receive line is coupled to the transmitter  and
>the  transmit line is coupled to the radio receiver.  This  is  a
>fast  way to put together  a phone patch and may be adequate  for
>VOX use.
>
>     A better patch can be built by using a network removed  from
>a  phone or purchased from a local telephone supply house.   This
>approach  offers the added advantage of being able to  adjust  or
>null the sidetone.  The circled letters in figs. 4 and 6 refer to
>the  markings on the network terminal block.  These  letters  are
>common to all United States networks made by Western Electric (AT
>&  T), ITT, Automatic Electric, Comdial, Stromberg  Carlson,  and
>ATC.
>
>     To  make  sidetone  adjustable, remove R4  (R5  in  European
>networks)  and  replace it with R11 (for  European  networks  use
>R12).   The Western Electric Network comes  point-to-point  wired
>and sealed in a can;  the other networks are mounted on PCBs.  To
>remove  R4 from the Western Electric network, the can has  to  be
>opened  by bending the holding tabs.  Don't be surprised to  find
>that  the network has been potted in a very sticky, odious  paste
>that has the texture of hot chewing gum and the odor of  unwashed
>shirts.  (This material - alleged to be manufactured according to
>a  secret formula - will not wash off with soap and  water.   The
>phone company has a solvent for it, but because one of the secret
>ingredients is said to be beeswax, ordinary beeswax solvents such
>as  gum  turpentine, mineral turpentine (paint thinner  or  white
>spirit)  and  kerosene  will work.)  To remove the  bulk  of  the
>potting  compound,  heat the opened can for 30 minutes in  a  300
>degree F (148 degree C) oven, or apply heat from a hot  hairdryer
>or heatgun.  You can also put the can out in the hot sun under  a
>sheet  of  glass.  Don't use too much heat  because  the  plastic
>terminal strip may melt.  Even with a film of compound  remaining
>on it, the network can be worked on.
>
>
>Using a Patch
>
>     For efficient use, a patch should have a telephone connected
>in parallel with it.  This enables the operator to dial,  answer,
>and  monitor  calls  to and from the patch, as well  as  use  the
>handset for joining in conversations or giving IDs.
>
>     One useful modification to the control telephone is adding a
>mute  switch to the handset transmitter.  This allows  monitoring
>calls without letting room noise intrude on the line.  It's  also
>a  good modification for high noise environments,  where  ambient
>noise enters through the handset transmitter and is heard in  the
>receiver,  masking  the incoming call.   Muting  the  transmitter
>makes calls surprisingly easy to hear.  The mute switch can be  a
>momentary switch used as a "Push-To-Talk" (PTT) or a Single  Pole
>Single  Throw (SPST) mounted on the body of the phone  for  long-
>term monitoring.  The switch should be wired as Normally  Closed,
>so  that the transmitter element is muted by shorting  across  it
>(see  fig.4).   This makes the mute "clickless." If  the  monitor
>phone uses an electret or dynamic transmitter it should still  be
>wired as shown in fig.4.
>
>     Transmit  and receive levels on the phone line are a  source
>of  confusion  that  even  telephone  companies  and   regulatory
>agencies  tend  to  be vague about.  The  levels,  which  can  be
>measured  in  various ways, vary.  But all  phone  companies  and
>regulatory  agencies  aim for the same goals;  enough  level  for
>intelligibility,  but  not enough to cause crosstalk.   The  most
>trouble-free  way  to set the outgoing level on the patch  is  to
>adjust  the  feed onto the phone line until  it  sounds  slightly
>louder  than the voice from the distant party on the phone  line.
>If  the level out from the patch is not high enough, the  distant
>party will ask for repeats and tend to speak louder to compensate
>for  a "bad line."  In this case, adjust the level to  the  patch
>until  the other party lowers his or her voice.  The best way  to
>get a feel for the level needed is to practice monitoring on  the
>handset  by  feeding a broadcast station down the phone  line  to
>another  Amateur  who can give meaningful signal  reports.   It's
>difficult to send too much level down the phone while  monitoring
>because  the  signal  would  simply be  too  loud  to  listen  to
>comfortably.  The major problem is sending too little signal down
>the line.
>
>     Coupling  the phone line into the radio transmitter  is  not
>much  more difficult than adjusting a microphone to work  with  a
>radio  transmitter.   Depending  on  the  setup,  the  RF  output
>indication  on  a wattmeter, the ALC on the transmitter  or  even
>listening  to the transmitted signal on a monitor  receiver  will
>help  in adjusting the audio into the radio  transmitter.   Phone
>lines  can  be  noisy,  and  running  too  much  level  into  the
>transmitter  and  relying on the ALC to set  the  modulation  can
>cause  a fair amount of white noise to be transmitted.   Watching
>the RF output while there are no voice or control signals on  the
>line  will  help  in  adjusting  for  this.   VOX  operation  can
>alleviate  the problem of noise being transmitted  during  speech
>pauses.
>
>     A  hybrid patch used for VOX operation needs to be  adjusted
>carefully  for  good performance.  If it has a  null  adjustment,
>this  should be set before adjusting the VOX controls.   Using  a
>separate receiver/transmitter setup is the easiest to adjust  the
>patch.    The  phone  line  should  be  attached  to   a   silent
>termination:  the  easiest way to do this is to dial  part  of  a
>number; another way to do it is call a cooperative friend.   Tune
>the  shack receiver to a "talk" broadcast station or use the  BFO
>as  a heterodyne.  With the transmitter keyed into a dummy  load,
>set  the  null  adjustment potentiometer R11  (R12  for  European
>phones)  for  a minimum RF output on the  transmitter.   Using  a
>transceiver, place an oscilloscope or audio voltmeter across  the
>microphone input terminals and, while receiving a signal,  adjust
>for  the  lowest voltage.  For proper operation,  it's  important
>that the phone be connected to the patch during these adjustments
>since  the  hybrid  relies  on  all  inputs  and  outputs   being
>terminated.
>
>
>Reference
>
>1. Julian Macassey, N6ARE, "Understanding Telephones," ham radio,
>September 1985, page  38
>
>
>Bibliography
>
>Rogers, Tom, You and Your Telephone, Howard W. Sams & Co.,  Inc.,
>Indianapolis, Indiana 46206. ISBN No. 0-672-21744-9.
>
>Bell System Technical Reference 48005; Telephones, January, 1980.
>
>British  Standard  Specification  for  General  Requirements  for
>Apparatus for Connection to the British Telecommunications Public
>Switched Telephone Network.  BS 6305.
>
>Certification  Standard  for  Voice-Type Terminal  Equipment  and
>Connectors, No.CS-01 and No.CS-03, Department of  Communications,
>Government of Canada.
>
>FCC  Rules  and Regulations: Part 68 -  connection  of  Terminal
>Equipment  to  the Telephone Network,  United  States  Government
>Printing Office, 1982.
>
>                           End of Text
>
>                   ----------------------------
>
>
>                    Fig 1. Simple Phone Patch
>
>     Tip  \                   C5
>     O----.\---o---------o----||----------O
>          .    |         |
>          .    |         /
>        S1.    |       R6\       Shielded
>          .    |         /       Wire
>     Ring \    |         |    C5 To Transmitter
>     O---- \--------o----o----||---o------O
>               |    |              |
>               |    |              |
>               |    |            -----
>               |    |             ---
>               |    |              -
>               |    |         C5
>               |    |---------||---o------O
>               |                   |
>               |                   \ Shileded
>               |                 R7/ Wire
>               |                   \ To Receiver
>               |              C5   |
>               ---------------||---o------O
>                                   |
>                                   |
>                                 -----
>                                  ---
>                                   -
>
>
>                 -------------------------------
>
>                    Fig 2. Basic Phone Patch
>
>
>
>      Tip \     R1A
>     O---o.\o--/\/\/-----o-----  -------o----o----O
>          .              |    |  |      |    | To Tx
>          .              |    |  |      |    |
>          .              |    )||(      |    |
>          .             ---   )||(   C1---   -----O
>        S1.         MOV ^ ^ T1)||(     ---     To Rx
>          .             ---   )||(      |
>          .              |    )||(      | Shielded
>          .              |    |  |      | Cable
>      Ring\     R1B      |    |  |      |    Common
>     O---o \o--/\/\/-----o-----  -------o----o----O
>                                             |
>                                             |
>                                           -----
>                                            ---
>                                             -
>
>                             ------------------
>
>
>                   Fig. 3 Improved Phone Patch
>
>
>             ----
>     Tip   \ |  |    R1A
>     o----o.\o  o---/\/\/--o-------||(-----------------o
>          |.    |          |      |||(
>          |.    |          |      |||( 8 Ohms   To RX
>          |.    |          |      |||(   Shielded cable
>        --|.    |          |      |||(------------o----o
>        |  .    |          |   T2 )||             |
>        | |-----|     MOV ---     )||(----o----o  |
>        | |.              ^ ^     )||(    |    |  |
>        | |. S2 Hksw      ---     )||(600 | C1 \  | R10
>        --------           | 600  )||(   ---   /<------o
>          |.    |          | Ohms |||(   ---   \  | To TX
>          |.    |          |      |||(Ohms|    /  | Shielded
>      Ring|\    |   R1B    |      |||(    |    |  | Cable
>     o----o \o  o--/\/\/---o-------  (----o----o--o----o
>             |  |                                 |
>             ----                               -----
>                                                 ---
>                                                  -
>     NOTE: S2 Hook Switch is also a polarity reversal switch.
>
>
>
>
>                    -------------------------
>
>Fig  4.  Typical U.S. Network (425B). Note: Circled  letters  are
>marked  on  Network Interconnection  block  terminals.  Component
>values may vary slightly between manufacturers.
>
>
>
>

>
>
>
>                         |-------------------|
>                       ..|...................|
>                       . |                  .|
>     Sidetone balancing. |    C3            .|
>     impedance & loop  . |    | |           .|
>     compensation. >>> . o----| |-------o   .|
>                       . |    | |       |   .|
>                       . |              |   .|
>                       . |    |<| VR2   |   .|
>                       . o----| |-------o---.|
>                       . |    |>|          |.|
>                       . |                 |.|
>                       . |   R4            |.|
>                       . o---\/\/\/-----|  |.|
>                       ..|..............|..|.|
>                         |              |  | |
>                         |        . (GN)|  | |
>                     (R) -----)||(------|-------o-----|
>                         TA1 1)||(5 TC  |  | |  |     |
>               Loop           )||(      |  | |  |     |
> TIP    \      Compensation  2)||(6     |  | | ---    |

[31/200] (?-AQZKSRE):

32/200       [1] Networked alt.2600
Title:       haq faq post
Date:        Thu, 27 Oct 1994 19:22:26 UTC (6 days old)
Origin:      anon.penet.fi (Unknown) [?]
From:        an116797 @anon.penet.fi Internet

> o-----o.\----------o---------)||(------o  | | ^ ^ RX O
>        .           |   (RR) . ||       |  | | ---    |
>        .           |          ||       |  | |  |VR60 |
>        .           \ 180      ||   C2 --- | |  |     |
>        .           / Ohms     ||      --- | |--o-----o
>        .  (F) C4   \          ||       |  |    |     |
>   S1   .   o--||---|          ||       |  |    |     |
>  HKSW  .          ---       . || .     |  |    o     |
>        .          ^ ^   -----)||(------o---   \   TX O

>        .      VR1 ---   |   3)||(7           S3|     |
>        .           |    |TA2 )||(  TB          |     |
>  RING \.           |    |   4)||(8       R3    |     |
> o----o \-----------o---------)||(---o----/\/\/-o------
>      (L2)               | (C)       |         (B)
>            ^            |           |
>        Hookswitch        ------------
>
>
>
>                       -------------------------
>
>
>
>     Fig. 5. Typical European Network
>
>
>      A  \
>     o--o.\---------o----o----o-------|
>         .          |    |    |       |
>         .          | C4 |    |       |
>         .          |   ---   \       |
>         .          |   ---   / R5    |
>         .          |    |    \       |
>         .          |    |    |       |
>         .          |    -----o----)|||
>         .          |              )|||
>     S1  .          |              )||o------o-----
>    HKSW .          |         200  )|||   VR |    |
>         .       TX O          Ohms)|||   60 |    |
>         .          |              )||(    -----  |
>         .          |              )||(     ^ ^   O RX
>         .          ---------------|||(    -----  |
>         .                     50  )||(60    |    |
>         .                     Ohms)||(Ohms  |    |
>      B \.                         )||(------o-----
>     o--o\-------------------------)||
>
>
>
>                        ----------------------------
>
>
>
>     Fig. 6. Deluxe Phone Patch
>
>
>
>
>                         |-------------------|
>                         |                   |
>                         |                   |
>                         |    C3             |
>                         |    | |            |
>                         o----| |-------o    |
>                         |    | |       |    |
>                         |              |    |
>                         |    |<| VR2   |    |
>                         o----| |-------o--- |
>                         |    |>|          | |
>                         |                 | |
>                         |   R4            | |
>                         o---\/\/\/-----|  | |
>                         |      ^ or R11|  | |
>                         |      |-------|  | |
>                         |        . (GN)|  | |
>                     (R) -----)||(------|-------------
>                         TA1 1)||(5 TC  |  | |       |
>                              )||(      |  | |       |
> TIP    \    R1A             2)||(6     |  | |    R12/   To TX
> o-----o.\--/\/\/---o---------)||(------o  | |       \<---------
>        .           |   (RR) . ||       |  | |       /
>        .           |          ||       |  | |       |
>        .           \ R2       ||   C2 --- | |--o----|---|------
>        .           /          ||      --- |    |    |  ---
>        .           \          ||       |  |    | R12\   -
>   S1   .           |          ||       |  |    |    /<---------
>  HKSW  .          ---       . || .     |  |   ---   \   To RX
>        .          ^ ^   -----)||(------o---   ---   |
>        .      VR1 ---   |   3)||(7          C1 |    |
>        .           |    |TA2 )||(  TB          |    |
>  RING \.   R1B     |    |   4)||(8       R3    |    |
> o----o \---/\/\----o---------)||(---o----/\/\/-o------
>      (L2)               | (C)       |         (B)
>                         |           |
>                          ------------
>
>
>Note:  T1  600 Ohm 1:1 Transformer would be between  R1  and  the
>line.
>
>
>                    -------------------------
>
>
>     Parts List
>
>
>
>     Item      Description
>
>     C1        0.1 uF (see text)
>     C2        1.5 to 2.0uF (Depending on manufacturer)
>     C3        0.47 uF Not used in all networks
>     C4        0.1 uF
>     C5        2.0 uF 250 Volt Mylar Film (see text)
>     MOV       130 to 250 Volt MOV (see text)
>     R1A,B     100 to 270 Ohms (see text)
>     R2        180 to 220 Ohms (depending on manufacturer)
>     R3        22 Ohms
>     R4        47 to 110 Ohms (depending on manufacturer)
>     R5        1 Kilo Ohm
>     R6        1 Kilo Ohm (see text)
>     R7        10 Ohm (see text)
>     R10       1 Kilo Ohm potentiometer (see text)
>     R11       200 Ohm potentiometer (see text)
>     R12       2 Kilo Ohm potentiometer (see text)
>     S1        DPST or Hookswitch
>     S3        NC Momentary switch (see text)
>     T1        600 Ohm 1:1 transformer
>     T2        600 Ohm primary. 600 Ohm and 8 Ohm secondary (see text)
>     T3        Network Transformer
>     VR1       Silicon Carbide Varistor or Back-to-back Zener
>     VR2       Silicon Carbide Varistor or Back-to-back Zener
>     VR60      Silicon Carbide Varistor or Back-to-back Zener
>
>
>                        END
>
>--
>Julian Macassey, [e-mail]  N6ARE@K6VE.#SOCAL.CA.USA.NA
>742 1/2 North Hayworth Avenue Hollywood CA 90046-7142 voice [phone]
>
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