Goto Section: 68.300 | 68.317 | Table of Contents
FCC 68.316
Revised as of October 1, 2008
Goto Year:2007 |
2009
Sec. 68.316 Hearing aid compatibility: Technical requirements.
A telephone handset is hearing aid compatible for the purposes of this
section if it complies with the following standard, published by the
Telecommunications Industry Association, copyright 1983, and reproduced by
permission of the Telecommunications Industry Association:
Electronic Industries Association Recommended Standard RS–504 Magnetic Field
Intensity Criteria for Telephone Compatibility With Hearing Aids
[ Prepared by EIA Engineering Committee TR–41 and the Hearing Industries
Association's Standards and Technical Committee ]
Table of Contents
List of Illustrations
1 INTRODUCTION
2 SCOPE
3 DEFINITIONS
4 TECHNICAL REQUIREMENTS
4.1 General
4.2 Axial Field Intensity
4.3 Radial Field Intensity
4.4 Induced Voltage Frequency Response
Appendix A—Bibliography
List of Illustrations
Figure Number
1 Reference and Measurement Planes and Axes
2 Measurement Block Diagram
3 Probe Coil Parameters
4A Induced Voltage Frequency Response for receivers with an axial field
that exceeds −19 dB
4B Induced Voltage Frequency Response for receivers with an axial field
that exceeds −22 dB but is less than −19 dB
Magnetic Field Intensity Criteria for Telephone Compatibility With Hearing
Aids
(From EIA Standards Proposal No. 1652, formulated under the cognizance of
EIA TR–41 Committee on Voice Telephone Terminals and the Hearing Industries
Association's Standards and Technical Committee.)
1 Introduction
Hearing-aid users have used magnetic coupling to enable them to participate
in telephone communications since the 1940's. Magnetic pick-ups in
hearing-aids have provided for coupling to many, but not all, types of
telephone handsets. A major reason for incompatibility has been the lack of
handset magnetic field intensity requirements. Typically, whatever field
existed had been provided fortuitously rather than by design. More recently,
special handset designs, e.g., blue grommet handsets associated with public
telephones, have been introduced to provide hearing-aid coupling and trials
were conducted to demonstrate the acceptability of such designs. It is
anticipated that there will be an increase in the number of new handset
designs in the future. A standard definition of the magnetic field intensity
emanating from telephone handsets intended to provide hearing-aid coupling
is needed so that hearing-aid manufacturers can design their product to use
this field, which will be guaranteed in handsets which comply with this
standard.
1.1 This standard is one of a series of technical standards on voice
telephone terminal equipment prepared by EIA Engineering Committee TR–41.
This document, with its companion standards on Private Branch Exchanges
(PBX), Key Telephone Systems (KTS), Telephones and Environmental and Safety
Considerations (Refs: A1, A2, A3 and A4) fills a recognized need in the
telephone industry brought about by the increasing use in the public
telephone network of equipment supplied by numerous manufacturers. It will
be useful to anyone engaged in the manufacture of telephone terminal
equipment and hearing-aids and to those purchasing, operating or using such
equipment or devices.
1.2 This standard is intended to be a living document, subject to revision
and updating as warranted by advances in network and terminal equipment
technology and changes in the FCC Rules and Regulations.
2 Scope
2.1 The purpose of this document is to establish formal criteria defining
the magnetic field intensity presented by a telephone to which hearing aids
can couple. The requirements are based on present telecommunications plant
characteristics at the telephone interface. The telephone will also be
subject to the applicable requirements of EIA RS–470, Telephone Instruments
with Loop Signaling for Voiceband Applications (Ref: A3) and the
environmental requirements specified in EIA Standards Project PN–1361,
Environmental and Safety Considerations for Voice Telephone Terminals, when
published (Ref: A4).
Telephones which meet these requirements should ensure satisfactory service
to users of magnetically coupled hearing-aids in a high percentage of
installations, both initially and over some period of time, as the network
grows and changes occur in telephone serving equipment. However, due to the
wide range of customer apparatus and loop plant and dependent on the
environment in which the telephone and hearing aid are used, conformance
with this standard does not guarantee acceptable performance or interface
compatibility under all possible operating conditions.
2.2 A telephone complies with this standard if it meets the requirements in
this standard when manufactured and can be expected to continue to meet
these requirements when properly used and maintained. For satisfactory
service a telephone needs to be capable, through the proper selection of
equipment options, of satisfying the requirements applicable to its
marketing area.
2.3 The standard is intended to be in conformance with part 68 of the FCC
Rules and Regulations, but it is not limited to the scope of those rules
(Ref: A5).
2.4 The signal level and method of measurement in this standard have been
chosen to ensure reproducible results and permit comparison of evaluations.
The measured magnetic field intensity will be approximately 15 dB above the
average level encountered in the field and the measured high-end frequency
response will be greater than that encountered in the field.
2.5 The basic accuracy and reproducibility of measurements made in
accordance with this standard will depend primarily upon the accuracy of the
test equipment used, the care with which the measurements are conducted, and
the inherent stability of the devices under test.
3 Definitions
This section contains definitions of terms needed for proper understanding
and application of this standard which are not believed to be adequately
treated elsewhere. A glossary of telephone terminology, which will be
published as a companion volume to the series of technical standards on
Telephone Terminals For Voiceband Applications, is recommended as a general
reference and for definitions not covered in this section.
3.1 A telephone is a terminal instrument which permits two-way, real-time
voice communication with a distant party over a network or customer premises
connection. It converts real-time voice and voiceband acoustic signals into
electrical signals suitable for transmission over the telephone network and
converts received electrical signals into acoustic signals. A telephone
which meets the requirements of this standard also generates a magnetic
field to which hearing-aids may couple.
3.2 The telephone boundaries are the electrical interface with the network,
PBX or KTS and the acoustic, magnetic and mechanical interfaces with the
user. The telephone may also have an electrical interface with commercial
power.
3.3 A hearing aid is a personal electronic amplifying device, intended to
increase the loudness of sound and worn to compensate for impaired hearing.
When equipped with an optional inductive pick-up coil (commonly called a
telecoil), a hearing aid can be used to amplify magnetic fields such as
those from telephone receivers or induction-loop systems.
3.4 The reference plane is the planar area containing points of the
receiver-end of the handset which, in normal handset use, rest against the
ear (see Fig 1).
3.5 The measurement plane is parallel to, and 10 mm in front of, the
reference plane (see Fig 1).
3.6 The reference axis is normal to the reference plane and passes through
the center of the receiver cap (or the center of the hole array, for handset
types that do not have receiver caps).
3.7 The measurement axis is parallel to the reference axis but may be
displaced from that axis, by a maximum of 10 mm (see Fig 1). Within this
constraint, the measurement axis may be located where the axial and radial
field intensity measurements, are optimum with regard to the requirements.
In a handset with a centered receiver and a circularly symmetrical magnetic
field, the measurement axis and the reference axis would coincide.
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4 Technical Requirements
4.1 General .
These criteria apply to handsets when tested as a constituent part of a
telephone.
4.1.1 Three parameters descriptive of the magnetic field at points in the
measurement plane shall be used to ascertain adequacy for magnetic coupling.
These three parameters are intensity, direction and frequency response,
associated with the field vector.
4.1.2 The procedures for determining the parameter values are defined in
the IEEE Standard Method For Measuring The Magnetic Field Intensity Around A
Telephone Receiver (Ref: A6), with the exception that this EIA Recommended
Standard does not require that the measurements be made using an equivalent
loop of 2.75 km of No. 26 AWG cable, but uses a 1250–ohm resistor in series
with the battery feed instead (see Fig 2).
4.1.3 When testing other than general purpose analog telephones, e.g.,
proprietary or digital telephones, an appropriate feed circuit and
termination shall be used that produces equivalent test conditions.
4.2 Axial Field Intensity .
When measured as specified in 4.1.2, the axial component of the magnetic
field directed along the measurement axis and located at the measurement
plane, shall be greater than −22 dB relative to 1 A/m, for an input of −10
dBV at 1000 Hz (see Fig 2).
Note: If the magnitude of the axial component exceeds −19 dB relative to 1
A/m, some relaxation in the frequency response is permitted (See 4.4.1).
4.3 Radial Field Intensity .
When measured as specified in 4.1.2, radial components of the magnetic field
as measured at four points 90 ° apart, and at a distance ≥16 mm from the
measurement axis (as selected in 4.2), shall be greater than −27 dB relative
to 1 A/m, for an input of −10 dBV at 1000 Hz (see Fig 2).
4.4 Induced Voltage Frequency Response .
The frequency response of the voltage induced in the probe coil by the axial
component of the magnetic field as measured in 4.2, shall fall within the
acceptable region of Fig 4A or Fig 4B (see 4.4.1 and 4.4.2), over the
frequency range 300-to-3300 Hz.
4.4.1 For receivers with an axial component which exceeds −19 dB relative
to 1 A/m, when measured as specified in 4.1.2, the frequency response shall
fall within the acceptable region of Fig 4A.
4.4.2 For receivers with an axial component which is less than −19 dB but
greater than −22 dB relative to 1 A/m, when measured as specified in 4.1.2,
the frequency response shall fall within the acceptable region of Fig 4B.
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Appendix A—Bibliography
(A1) EIA Standard RS–464, Private Branch Exchange (PBX) Switching Equipment
for Voiceband Applications.
(A2) EIA Standard RS–478, Multi-Line Key Telephone Systems (KTS) for
Voiceband Applications.
(A3) EIA Standard RS–470, Telephone Instruments with Loop Signaling for
Voiceband Applications.
(A4) EIA Project Number PN–1361, Environmental and Safety Considerations for
Voice Telephone Terminals.
(A5) Federal Communications Commission Rules and Regulations, part 68,
Connection of Terminal Equipment to the Telephone Network.
(A6) IEEE Standard, Method for Measuring the Magnetic Field arould a
Telephone Receiver. (to be published)
[ 49 FR 1363 , Jan. 11, 1984, as amended at 61 FR 42187 , Aug. 14, 1996]
Goto Section: 68.300 | 68.317
Goto Year: 2007 |
2009
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