Telecom/1996-04-telecom-walnutcreek.iso/technical/radio-phone.interference

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From: Julian Macassey <[e-mail]>
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Subject: Re: Radio Interference to Phones
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                  TELEPHONE INTERFERENCE

                    (CAUSES AND CURES)

      Sooner  or  later, you are going to become the  victim,  or
cause of, interference to a telephone or phone system. You may be
lucky  and  only  know  someone  who  is  the  victim  of   phone
interference.

      The  sort of interference we are discussing here  is  Radio
Frequency  Interference  (RFI).  It is obvious that  RFI  can  be
caused by radio transmitters, and also TV transmitters. The radio
transmitters can be AM broadcast, Two Way, CB, Ham, FM  broadcast
and studio links. Less obvious can be garage door openers as well
as  anything  that  generates electric sparks  such  as  electric
motors and transformers that are breaking down.

      Any device that would also be registered with the FCC as  a
Part  15  Subpart  J device is liable to cause  RFI.  A  part  15
subpart  J  device  is  any device  using  a  microprocessor  and
generating square waves. This means any digital device, including
the onboard computer in the family chariot and the lawn sprinkler
timer.  Favorite  generators of RFI of this type that  are  often
overlooked are programmable scanners.

      Bear  in  mind also that many phones  today  are  "feature"
phones which means they too have microprocessors on board and can
interfere  with themselves, other phones, or even  nearby  radios
and  TVs.   Of all types of phones, the old style desk  phones  -
rotary types known as the 500 set and the Touch-Tone version 2500
set - are much much less susceptible to interference than  modern
electronic  phones.   Modern  electronic  phones  tend  to   have
transistors and integrated circuits in them. These semiconductors
act  as  detectors like the old crystal sets. The  amplifiers  in
these  modern phones then tend to amplify the  detected  signals.
The result...your good buddy from channel 16 tends to get on  the
phone  line with you. So a fast simple cure for interference  can
often be to drag the old black phone back out of the closet.

      There  is some hope when it comes to interference. The  FCC
has  issued  a  field bulletin on RFI.  The  document  is  called
"Bulletin FO-10, Telephone Interference".   It is reproduced here
(see  box)  and copies of it can be obtained from any  FCC  field
office.  Find  your nearest FCC office by looking up FCC  in  the
phone  book.  The  Bell System has  considered  the  problem  and
approach it from the viewpoint of interference to regular 500 and
2500  type phone sets. The Bell document concerning RFI is  known
as  a  Bell Systems Practice (BSP). The document is  BSP  Section
500-150-100.

      The  FCC  document is quite adamant  that  only  authorized
personnel  can  open phones to modify them against RFI  and  that
only telephone company personnel can add coils and capacitors  to
the telephone protector. Modifications to protectors and internal
modifications  to  phones are described here for  those  who  are
authorized to do such work.

      There  are  many  modifications that can  be  done  by  the
consumer.  Some  of these modifications are very  effective.  One
modification that can be done quickly and cheaply is the addition
of  ferrite cores to handset cords and line cords. Also  easy  to
add  are modular plug-in filters. Requiring more work is the  re-
routing of phone wire or the installation of shielded wire. Don't
forget  that  although  opening your phone or  fooling  with  the
protector  may be a no-no, you can do whatever you want with  the
wire in your home.

      Before  you tear  things  apart and  spend money, there are
a  few  things  to  check.  These  checks  can  be  done  with an
adjustable wrench and a screwdriver.  What is checked is anything
on  the  line  itself  that  could  be  acting  as  an antenna or
detector.  A  dirty  connection can work as a diode to  detect RF
signals.  Go over  the internal wiring looking for the following:

 1.   Corroded connections. Clean and tighten.

 2.   Loose wire terminations, including set wiring and all jacks
and junction boxes. Tighten any loose screws.

 3.   Abandoned wire still connected to the line. Remove any wire
not connected to a working phone.

 4.    Old  unused devices still connected to  the  line.  Remove
abandoned phone answering machines, old telephones and bells etc.


     If  any of the above is what is causing the RFI,  until  you
fix  them,  there is little hope that anything else you  do  will
cure  the  problem.  All of the above fixes  are  legal  for  any
subscriber  to  do  without  falling foul of  the  FCC  or  local
Telephone  Company. The exception is of course those  with  party
lines.  Party line subscribers should be wary of  adjustments  to
wires  and  telephones and call in the phone company.  There  are
many ways of wiring party lines and the telephone company will be
familiar with their own equipment. If you mess up the wiring of a
party line phone, it may cease to ring or refuse to dial.

      The  other  legal  "do it yourself" fix  is  attachment  of
toroid  cores.  These cores look like small black  doughnuts,  by
wrapping  wire round a ferrite core a simple effective RF  filter
or  choke can be made. Ferrite cores are frequency selective,  by
the choice of the right material, interference can be effectively
hit on the head.

          With  modern phones, the most RF sensitive part of  the
phone is the electret microphone and its preamplifier circuit. By
application of ferrite cores to the handset cord, there is a fair
chance  of  easily  and cheaply fixing the problem.  If  you  are
hearing radio signals on the phone, there is a way of checking if
the microphone/handset cord is to blame. Dial a partial number to
give you silence, listen for the interfering signals and grab the
handset  cord. If the signal changes in volume - gets  better  or
worse - try a ferrite core.

          The best source of ferrite cores in small quantities is
Amidon   Associates,  12033  Otsego  street,   North   Hollywood,
California  91607. PHONE: [phone]. Amidon Associates  have
several ferrite "mixes" available. For interference from 500  Khz
to  10  Mhz,  i.e.  AM broadcast RFI,  they  recommend  their  75
material. For interference from 1 to 30 Mhz they recommend  their
73  material. The 73 material should take care of all short  wave
Ham and CB interference. For low VHF and channel 2-7 RFI you  can
try  a ferrite core made with the 43 material which  should  take
care  of  RFI  between  1 and 70MHz. For  best  results  use  the
material  that has the lowest cutoff point for your  problem.  If
the local AM transmitter at 1070 KHz is your problem, use the  75
material, it will give much better attenuation at that  frequency
than the 73 material.

          For  a  handset cord, a half inch core is  ideal.  Wrap
four or five turns of the handset cord through the core and  plug
it  back  into the handset. The cord can be held  in  place  with
black  vinyl tape or glue, hot melt glue works  well.  Experiment
with  the positioning of the core. Often having the core  by  the
handset  works  best, other times plugging in the cord  with  the
core by the body of the phone is better. Sometimes a core at each
end  of  the cord is needed to do the trick. The cores  may  look
kinda clunky, but if they provide relief easily and cheaply,  who
are you to complain.

     The numbers for the half inch cores are: FT-50A-75,  FT-50A-
73  and FT-50A-43. Yes you guessed it - the last two digits  tell
you  the material being used. For one and a half inch cores  used
with line cords explained below, the numbers are: FT-140-75.  The
last two digits being the same as for the half inch cores.

          For  RFI that you suspect to be entering via the  phone
line, wrapping the line cord round a large core can help. Usually
it  is  best to place the core at the telephone end of  the  line
cord. Though like all RFI cures, experimentation, otherwise known
as "suck it and see", does a better job than hard and fast rules.
With  the  large core on the line cord, between  six  and  twenty
turns on the cord should do the trick. A core on each end of  the
line cord may help in stubborn cases.

          The  FCC in their document mention plug-in modular  RFI
filters.  Despite  their breezy assurance, these can be  hard  to
find  locally.  Those lucky enough to  have an AT&T  phone  store
handy  can  buy a device  called a "Radio Frequency  Filter",  it
will cost about $6.00 and is modular. All you have to do is  take
it  home and plug it in. Those far from an AT&T store  can  order
one  by phone. With credit card in hand, dial [phone]  and
ask for a Radio Frequency Filter.

          For   authorized  phone  repair   stations,   telephone
personnel and those willing to risk "Open circuit surgery", there
are several solutions. Using ferrite cores, twenty turns or so of
scrap  24 Gauge telephone wire can be wrapped round a  half  inch
ferrite  core.  Use two cores, one for Tip and one for  Ring  and
place them inside the phone. The same kind of cores and  windings
can   also  be  used,  inside  the  phone,  on  the   transmitter
(microphone) leads.

          For  those really handy with a smoking  soldering  iron
there  are  some  more fixes to try. For  phones  using  electret
microphones, some well placed capacitors may do the trick. Try  a
0.01 uF (10 Nf)  across  the  electret  element.  If that doesn't
work  try  the  same  value  of  cap  across  the hot side of the
element  to  the  "ground"  of  the  pc  board.   Regular  phones
with  carbon  transmitters can  be  helped  with a 0.01 or 0.1 uF
capacitor  across the  element.  Solder  the capacitor across the
contact fingers  in the  handset,  not  across the element, so if
the  transmitter  is  changed,  the RF  proofing  will  stay with
the  phone.   Also,  inside  the  phone,  a  0.1 uF (100 Nf) 250V
capacitor  across Tip  and  Ring  can  be   helpful.  The type of
capacitor to use is  a  Ceramic  or Mylar.

          For those with access to AT&T parts or wishing to  help
the  local phone company, there are a couple of bits  of  helpful
hardware  mentioned in Bell Systems Practice  500-150-100.  First
there is a coil that should be spliced into the phone line. It is
called  a 1542A inductor. It should be spliced into the  line  as
near  as the offending telephone set as possible. This means  put
it  right before the modular jack. It has six terminals, two  for
Tip, two  for Ring and two for a ground, should the  phone  still
need  a  ground (yellow wire) for the ringer or party  line.  The
ground  terminals  are not in any way connected to the  coil,  so
bringing  a ground to the inductor, unless needed in  the  phone,
will not help cure any RFI.

          The Bell document also mentions a capacitor, designated
a 40BA capacitor. It is actually four capacitors (see Fig 1)  and
the intent is to place a capacitor between each leg of the  phone
line  and ground. The 40BA is usually installed at the  telephone
protector.  There  is  always  a good  ground  available  at  the
protector,  often a heavy gauge solid, solid gray jacketed  wire.
Those  telephone  personnel  who do not have  access  to  a  40BA
capacitor  should  find  that  a couple  of  0.1  uF  250V  Mylar
capacitors  will  work just as well (see Fig 2). To  install  the
40BA  or 0.1uF capacitors, find the protector. The  protector  is
usually outside the building in a wall mounted small box, in  the
basement  or in a closet for businesses and apartment  buildings.
If the phone line comes in on overhead cable, the protector  will
be  in  the  first  box the cable  goes  to  after  entering  the
premises.

          That should be some help in beating the problem.  Don't
forget that some types of phones are more sensitive than  others.
Some  cases may be so severe that nothing helps. AT&T  no  longer
have  RFI  proofed phones available, although an old  style  desk
phone  with some capacitors added will be pretty immune  to  RFI.
Alas  AT&T  no  longer makes old style 500 and  2500  desk  sets,
although they sell reconditioned ones. Several manufacturers such
as  ITT,  Comdial,  and Northern Telecom  still  make  old  style
phones.

                            END
Julian Macassey, N6ARE
742 1/2 North Hayworth Avenue
Hollywood
California 90046-7142

PHONE: [phone]

This article appeared on Page 56 of the Feb 1988 edition of
Popular Communications Magazine.

--
Julian Macassey, n6are  [e-mail]  ucla-an!denwa!bongo!julian
742 1/2 North Hayworth Avenue Hollywood CA 90046-7142 voice [phone]

From @hub.eecs.nwu.edu:[e-mail] Fri May  3 01:10:32 1991
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The  folowing is a "Bell Systems Practice" on telephone RFI.
The document is complete apart from two photographs of the  1542A
inductor  and the 40BA capacitor.  Also missing is the  schematic
and  and  diagram of the 425J schematic.  The values of the  40BA
capacitor are shown,  normally this capacitor would be a 250 Volt
Mylar type. There is no value for the 1542A inductor.


BELL SYSTEM PRACTICES                         SECTION 500-150-100
AT&TCo Standard                             Issue 7, January 1974


                    RADIO SIGNAL SUPPRESSION
                       FOR TELEPHONE SETS


1.    GENERAL

1.01  This section contains information on the reduction of radio
interference in telephone sets.

1.02  This section is reissued to:

     o Add information on single slot coin telephones

     o Show 241A amplifier replaced by 241B amplifier.

1.03   Radio interference frequently occurs where a radio station
is located near telephone facilities.  Generally the radio signal
is  picked  up  by  the  wire  which  acts  as  an  antenna,  and
demodulated (changed to audio frequency) by nonlinear components,
such as varistors,  transistors and diodes in the telephone  set.
HOWEVER  DEMODULATION  CAN ALSO RESULT FROM CORRODED  CONNECTIONS
AND TERMINATIONS.

1.04   Before ordering a telephone set modified for radio  signal
suppression, check for the following:

     o Corroded connections (inside and outside plant)

     o Loose wire terminations (including set wiring)

     o Abandoned drop wire still connected to line

     o Inside wire connected but not used

     o Foreign attachments


     Installing  a  modified  telephone  set  on  the   customers
     premises  will not be effective if demodulation is caused by
     any of the above conditions.



1.05  Telephone set components that may act as demodulators are:

     o Speech equalization varistors in networks

     o Transistors in amplifiers of some networks and handsets

     o Varistors and transistors in TOUCH-TONE dials

     o Diodes in polarity guards

     o Click suppression varistors across receiver units

     o Carbon transmitters


1.06  With the introduction of the 425J and 4010E  networks,  the
cause  of  radio signal demodulation in networks has  effectively
been  minimized.   In  these  networks  the  speech  equalization
varistors have been replaced by resistors and a strapping  option
that provides speech equalization.


1.07  All telephone sets,  excluding coin, will be available from
the   local   distributing  house  modified  for   radio   signal
suppression.  Modification  will  include  changing to  new  type
network,  where applicable,  and placing bypass capacitors across
all  other components that may act as demodulators as  listed  in
1.05.


R    BEFORE  ORDERING  A MODIFIED TELEPHONE SET  MAKE  SURE  THAT
E    DEMODULATION  IS NOT OCCURRING EXTERNAL TO THE TELEPHONE SET
A    (See 1.04)
D

1.08  Single slot coin telephones are not modified at the service
center, and where radio frequency is a problem, it is recommended
that  a  40BA capacitor and/or a 1542A inductor be added  to  the
protector and connecting block.

1.09   Where  demodulation  is  attributed  to  components  in  a
telephone  set,  or  associated voice  coupler,  in  addition  to
changing  to  a  modified  set  it is  recommended  that  a  40BA
capacitor be placed at the protector and a 1542A inductor at  the
connecting  block.  Refer  to section in Division 463  for  voice
coupler modifications. The capacitor will bypass, to ground radio
signals  picked up by the drop wire while the inductor will  tend
to attenuate radio signals picked up by the inside wire.


1.10   Where  an adjunct (TOUCH-TONE phone) dial forms a part  of
the customers equipment and a modified telephone set is installed
for radio interference reasons,  the adjunct dial should also  be
replaced by one modified for radio suppression.


1.11    MD  telephone  sets  will  not  be  modified  for   radio
suppression.  Where  a telephone set rated MD is encountered,  it
should  be replaced by an equivalent set in the  current  series,
modified for radio suppression.


1.12   If  possible  arrange for operation of the  radio  station
during  the  trouble  visit in order that  the  effectiveness  of
corrective measures taken may be evaluated immediately.


2.    IDENTIFICATION

2.01  Suppression Devices

  (a) 425J Network (Fig. 1):

    o Eliminates   radio   interference  by  having  the   speech
      equalization   varistors  replaced  by  resistors   and   a
      strapping option ("H" and "J" leads)

    o Can be used for rotary or TOUCH-TONE dial applications

    o Contains  an equalization network for TOUCH-TONE dials ("X"
      Terminal)

  (b) 4010E Network (Fig. 2):

    o Similar to 425J

    o Strapping option consists of "N" and "V" leads

  (c) 1542A Inductor (Fig. 3):

    o Attenuates RF line current

    o Can be substituted for the 42A connecting block

    o Removable  link between terminals B and Y  (current  models
      only). Required when used as connecting block for telephone
      sets with dial lamps or with 30A voice coupler.


  (d) 40BA Capacitor (Fig. 4):

    o Located at protector to bypass RF signals to ground


2.02  TELEPHONE SET MODIFICATION BY LOCAL DISTRIBUTING HOUSE

  (a) Telephone sets,  except coin, currently using the 425- or
        4010-type networks will be modified as follows:

    o Existing  network  replaced  by a 425J  or  4010E  network,
      whichever is applicable

    o TOUCH-TONE  dial  will  have  bypass  capacitors  installed
      across  the varistors and transistors and will also have an
      additional  (red-slate) lead soldered to the  "X"  terminal
      which in turn connects to the "X" terminal on the network.

    o Bypass  capacitors installed across all other components of
      the  telephone set that may act as  demodulators,  such  as
      transmitter unit, receiver unit, transistors in amplifiers,
      polarity guards, etc.

  (b) TRIMLINE  telephones  will  be modified  by  having  bypass
      capacitors placed across all the components in the set that
      may act as demodulators.

  (c) Modified sets will not be recoded but will be identified in
      some manner by the local distributing house.


2.03  TOUCH-TONE dials and all G-type handsets will be  available
from the local distributing house modified for radio suppression.
These  will  be used where an adjunct dial must be  installed  or
where  the  dial  or  handset must be  replaced  for  maintenance
reasons.


2.04 Other modified telephone set components include 241B,  242B,
and  277A  amplifiers;   D-180191  and  D-180191  polarity  guard
assemblies;   and  694A  and  B  subsets.  Modified  versions  of
additional  items will be made available in the future when  they
are needed.


3. ORDERING GUIDE

    o Capacitor, 40BA

    o Inductor 1542A-

      -49 Gray, -50 Ivory

    o Set, Telephone--RF Modified

    o Set, Telephone, Hand 220A--RF Modified

    o Set, Telephone, Hand 2220B--Modified

    o Dial--(TOUCH-TONE dial only) RF Modified

    o Set, Hand G--RF Modified



4.    INSTALLATION


4.01 TELEPHONE SETS EQUIPPED WITH 425J OR 4010E NETWORKS

      (a) Installed in usual manner

      (b) For  connections see connection section  of  type  set
          modified

      (c) Sets are shipped with speech equalization option leads
          insulated and stored:

          (1) For loops greater than 500 ohms leave insulated and
          stored.

          (2)  For  loops  500 ohms or less connect  "H"  or  "N"
          (Yellow)  and  "J"  or  "V"  (Orange-Black)  leads   to
          terminals  RR and R respectively,  on the 425J or 4010E
          network.


4.02  Modified TRIMLINE Telephones

      (a) Install in usual manner

      (b) See Section 502-321-400 for connections


4.03  1542A Inductor (Fig. 5)

      (a) Use as connecting block for telephone set cord.

      (b) Locate as near as possible to wall-type sets.


4.04  40BA Capacitor (Fig. 6)

      (a) Install near and connect to protector with as short as
          possible inside wire.

      (b) Station wires must connect to the capacitor

      (c) Mounted inside when outside protector is used

      (d) PROTECTOR GROUND MUST BE UPGRADED TO THE BEST  POSSIBLE
          GROUND AVAILABLE.


5. MAINTENANCE


5.01   Normal maintenance can be performed on modified  telephone
sets. Modified TOUCH-TONE dials and G-type handsets are available
from the local distributing house for maintenance.

                               END



Fig. 3--1542A Inductor schematic


                          1542A
                         INDUCTOR
                    __________________
RING               |R1              R |            RED
-------------------|-o--^^^^^^^^^^--o-|----------------
                   |                  |
TIP                |G1              G |          GREEN
-------------------|-o--^^^^^^^^^^--o-|----------------
                   |                  |
GROUND             | B              Y |         YELLOW
-------------------|-o-------\------o-|----------------
        LINE       |__________\_______|  SET CORD
                               \
                                \
                          REMOVABLE LINK



Fig. 4--40BA Capacitor Schematic


            0.25uF   0.25uF     0.25uF  o.25uF
      --------| (------| (----o---| (-----| (------|
      |                       |                    |
      |                       |                    |
      |                       |                    |
      |                       |                    |
      |                       |                    |
      |                       |                    |
      |                       |                    |
      |                       |                    |
      o                       o                    o
     TIP                   GROUND                RING



--
Julian Macassey, n6are  [e-mail]  ucla-an!denwa!bongo!julian
742 1/2 North Hayworth Avenue Hollywood CA 90046-7142 voice [phone]

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From: Julian Macassey <[e-mail]>
Newsgroups: comp.dcom.telecom
Subject: Re: Radio Interference to Phones
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Date: 2 May 91 07:40:31 GMT
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                   INFORMATION BULLETIN
             Federal Communications Commission
                  Field Operations Bureau
_________________________________________________________________
                     Telephone Interference
                     ----------------------

This  document has been prepared to assist you  in  understanding
why  interference  to your telephone system  occurs.  Recommended
solutions   for  you  and  your  authorized   telephone   service
technician are also provided.

                                        Bulletin FO-10
                                        September 1986


                WHY TELEPHONE INTERFERENCE OCCURS

Telephone   technology  today  uses  circuitry  which,   if  left
unprotected,  will  respond to the radio frequency  (rf)  signals
from nearby radio transmitters such as Amateur, Citizens Band and
AM/FM  broadcast stations.  When the telephone circuitry responds
to the rf signal you hear the interference on your telephone. The
rf  signal can be entering at the telephone instrument or on  the
inside or outside wiring.

Cordless telephones are also susceptible to rf signals.  Cordless
phones  are low-power transmitters using  radio  frequencies.  As
with  any radio transmitter,  they can receive interference  from
other  nearby transmitters.  Interference can also occur if  your
neighbor's  cordless  phone is using the same radio frequency  as
yours.  Since  the FCC does not offer interference protection  to
cordless   telephones,   you  should  contact  your   dealer   or
manufacturer for assistance when interference occurs.


                      RECOMMENDED SOLUTIONS

The  installation  of  a modular filter is suggested as  a  first
step.  Modular filters are available from most telephone  stores.
It can be easily installed by you if your telephone has a modular
jack.  You may wish to verify if the filter can be returned for a
refund if it does not eliminate the interference.
The  effectiveness of filtering may vary according to the type of
telephone  you  are  using.  Also,  modifying  certain  types  of
telephones,  as suggested below, may be impractical or expensive.
When  it  is,  consider changing to another brand or  model  with
better interference protection.

If you have taken the above steps,  and the interference is still
present, the telephone instrument or wiring will probably have to
be  filtered.  YOU  SHOULD NOT INTERNALLY MODIFY  THE  INSTRUMENT
YOURSELF  NOR  ATTEMPT  FILTERING  OUTSIDE  PHONE   LINES.   ONLY
AUTHORIZED  SERVICE  TECHNICIANS MAY INTERNALLY MODIFY  TELEPHONE
INSTRUMENTS.  ONLY TELEPHONE COMPANY PERSONNEL MAY FILTER OUTSIDE
TELEPHONE  LINES.  This  rule is designed to ensure  that  phones
continue to comply with FCC registration standards.

Interference  picked up by the inside wiring can be corrected  by
installing  SHIELDED  inside wiring.  If you have  subscribed  to
inside line maintenance,  the local telephone company can install
shielded  inside wiring for you.  If you have NOT  subscribed  to
inside line maintenance,  they can still perform this service for
a fee.


                   SERVICE TECHNICIAN SECTION

If  your customer has tried the modular filter and shielded their
inside wiring and the interference is still present, we recommend
you filter the inside of the telephone instrument.
Interference   in  older  rotary  dial  phones  (without  special
features)  can  usually  be  resolved  by  bypassing  the  carbon
microphone.  Install  a 0.001 mfd ceramic disc capacitor  in  the
back of the mouthpiece in the handset. Where possible, solder the
capacitor  directly  to the microphone contact fingers  with  the
shortest possible leads.

Phone instruments with special features such as memory, automatic
redial,  speakers, push-button dialling, and sound amplification,
contain  components which are sensitive to rf signals.  Shielding
and  bypassing of these components are necessary to  isolate  the
affected  circuit(s).  Refer to the design  specifications.  Bell
System  technicians may refer to the Bell Systems Practices Plant
Series Manual Section 500-150-100 for necessary modifications.

Another  possible  solution would be to  install  ferrite  cores.
These  are donut-shaped devices through which the phone cord  can
be wound.  Ferrite cores are available in various sizes.  Use one
with a hole large enough to permit passing the phone cord through
it two or three times.

To  install  a  ferrite core,  first disconnect  the  phone  cord
between  handset and telephone base.  Loop the phone cord through
the core two or three times.  Tape or fasten the core as close as
possible to the handset.  Reconnect the phone cord.  Two  ferrite
cores  on the handset might be necessary.  If so,  place one near
the handset and another near the telephone instrument.

If  the interference continues after filtering the phones  and/or
installing inside shielded wiring,  the interference is  probably
entering  the  system  through  the  outside  wiring.  The  local
telephone  company  service  department should be  contacted  for
assistance.  Only telephone company personnel may filter  outside
telephone  lines.  Two devices which may be used for  eliminating
outside interference are:

-a  40 BA capacitor installed at the service entrance  protector,
and

-a 1542A inductor installed at the connector block.

Your  next  step  would  be  to  have  the  telephone  instrument
filtered.   If  you  own  your  phone,   contact  the  dealer  or
manufacturer for assistance. If you lease your phone, contact the
local phone company's service department.  You may wish to  share
the  Service Technician Information section of this document with
the technician assigned to assist you.

Even  though you may be experiencing interference to  other  home
electronic entertainment equipment, such as televisions, stereos,
or  VCRs,  the telephone should be filtered.  If the rf signal is
entering  the  telephone system,  the interference  can  only  be
eliminated  at the point of entry.  Filtering or shielding of the
phone instrument also offers future protection to your  equipment
from other rf signals.

You  may  provide  to  the FCC the name  and/or  address  of  the
owner/operator   of  the  radio  equipment  involved  when  other
equipment  is receiving interference.  The FCC  will  communicate
with  that  person  to  determine  if  they  can  assist  you  in
eliminating the interference.  FCC office addresses are listed at
the end of this document.

     CAUTION:   Only    authorized   service   technicians    may
                internally  modify  telephone  instruments.  Only
                telephone  company  personnel may filter  outside
                telephone lines.
                                    END
--
Julian Macassey, n6are  [e-mail]  ucla-an!denwa!bongo!julian
742 1/2 North Hayworth Avenue Hollywood CA 90046-7142 voice [phone]