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TIA/EIA-PN-3-4558-RV1 Rev. A of TIA TSB121
Post - BALLOT EDIT’S VERSION
2.5mm Audio Interface for Mobile Stations – TTY
June 25, 2003
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TSB-121 COPYRIGHT PAGE
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(To be supplied by TIA)
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CONTENTS
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1. INTRODUCTION
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2. REFERENCES
- Signal Reference Level Considerations
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3. GENERAL INFORMATION AND OVERVIEW
- Audio Link Interface
- Suggested Labeling
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4. PHYSICAL INTERFACE
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5. ELECTRICAL CONTACTS AND CHARACTERISTICS
- Design Goals
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6. RECOMMENDED PHYSICAL PARAMETERS
- Critical Physical Dimensions of the 2.5mm Male connection.
- Critical Physical Dimensions of the 2.5mm Female connection
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7. INTERCONNECT OPTIONS
- Option 1: Headset Connection
- Option 2: TTY Adapter “Vendor Specific”
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ANNEX A: End-to-End Signal Path
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ANNEX B: Blocking Capacitors in TTY/TDD and Mobile Signal Paths.
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ANNEX C: Hearing Carry over (HCO) and Voice Carry over (VCO)
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CHANGE HISTORY
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1. INTRODUCTION
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This Telecommunications Systems Bulletin (TSB) describes a possible
implementation of the interface between a mobile station and a TTY.
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Recognizing that:
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 The FCC Rule and Order CC Docket No. 94-102 "E9-1-1/TTY
Compatibility" requires wireless service providers to support TTY
compatibility for contacting assistance in an emergency.
 The CTIA/PCIA TTY Forum requested that TIA TR-45 specify a
2.5mm connection with appropriate electrical parameters that would
allow reliable audio interconnection between TTY’s and mobile
wireless handsets.
 The majority of legacy TTY terminals only support audio connection
to the telephone network via:
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 Acoustic coupling utilizing the wire-line handset placed into
flexible cups designed for Type G or Type K handsets. .
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 FCC Type RJ-11 modular connection. (FCC Part 68 compliant)
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Due to the wide variety of shapes and sizes of modern wireless
handsets, neither of these modes of connections, to a TTY, is
applicable to mobile wireless handsets.
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This TSB specifies an interface that will support direct audio
connections between TTY’s and mobile wireless handsets.
Revision 1 is the result of several months’ testing, in real-world
situations, following the initial publication version of TSB-121.
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2. REFERENCES AND DEFINITIONS
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The following standards pertaining to mobile stations may be useful in implementing
this TSB. At the time of publication, the editions indicated were valid. All standards are
subject to revision, and parties to agreements based on this TSB are encouraged to
investigate the possibility of applying the most recent editions of the standards indicated
below.
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
TIA/EIA-690: Recommended Minimum Standard for 800 MHz Cellular Subscriber
Units
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ANSI/TIA/EIA-98-C: Recommended Minimum Performance Standards for Dual-Mode
Spread Spectrum Cellular Mobile Stations
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TIA/EIA-136-270-B (March 31, 2000) TDMA Third Generation Wireless - Mobile
Stations Minimum Performance
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A TIA/EIA standard for 2.5mm connectors was not found. Various commercial
vendor’s drawings were consulted to generate an acceptable average.
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Signal Reference Level Considerations:
Digital Voice coders and de-coders in modern non-analog subscriber’s mobile handsets
require advanced techniques to establish proper signal levels. Steady-state sine wave
signals may give inaccurate measurements.
 IEEE 269 and IEEE 661 define the measurement of sensitivity and the calculation of
loudness rating.
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Artificial conversational speech is a test signal generated by inserting pauses in the
continuous artificial voice signal described by ITU-T Recommendation P.50.
The on-off temporal characteristics of conversational speech are defined in ITU-T
Recommendation P.59.
This test signal is useful for evaluating devices that are sensitive to the on-off nature of
conversational speech.
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
ITU-T Recommendation P.50 (1993): "Artificial voices".
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
ITU-T, Recommendation P.56 (1993): “Objective Measurement of Active Speech
Levels”
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ITU-T, Recommendation P.59 (1993): “Artificial Conversational Speech”
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Typical parameters of simulated speech include long-term average spectrum, shortterm spectrum, instantaneous amplitude distribution, speech waveform structure, and
the syllabic envelope.
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ROLR - Receive Objective Loudness Rating, a measure of receive audio sensitivity.
ROLR is a frequency- weighted ratio of the line voltage input signal to a reference
encoder to the acoustic output of the receiver.
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TOLR - Transmit Objective Loudness Rating, a measure of transmit audio sensitivity.
TOLR is a frequency-weighted ratio of the acoustic input signal at the transmitter to
the line voltage output of the reference decoder.
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3. GENERAL INFORMATION AND OVERVIEW
This TSB describes a recommended audio connection between a TTY and a mobile
station through the use of a 2.5mm jack and a plug for the physical connection and
the specification of the preferred electrical characteristics.
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This interface is defined at a point between the modulator/demodulator of the TTY
and the audio input/output of the mobile wireless handset (See Figure 1).
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
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The interconnection cable is considered to be part of the TTY.
Audio Link Interface
Mobile
Station
TTY
Figure 1
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Suggested Labeling:
The following labeling may appear:
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Wireless/TTY Compatible
with Select TTY Terminals
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ISO International Symbol
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4. PHYSICAL INTERFACE
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o The physical connection, between the Wireless Device and the TTY,
is a three-conductor 2.5mm stereo jack and plug.
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o The handset side of the interface is a female 2.5mm connector,
and at the TTY side is a male 2.5mm connector.
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o The interconnection cable is considered to be part of the TTY.
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o This TSB is written from the wireless device’s view that utilizes
the female connector.
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5. ELECTRICAL CONTACTS AND CHARACTERISTICS
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TIP (TIP): MIC - Mobile Station Microphone (input to Mobile Station)
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CENTER (RING): SPKR - Mobile Station Speaker (out of Mobile Station)
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SLEEVE: GND – Ground and shield
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MIC
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SPKR
GND
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Design Goals
MOBILE SUBSCRIBER UNIT
TTY DEVICE
TRANSMIT (MS MIC Input)
MS Tx AC
Impedance
MS Tx DC
Impedance
TTY Tx Signal Level = -26dBV +/- 6dB
Input
 TTY Tx AC Output
Z  2k
Impedance
Z  150
[1] [3]
Input

R  2k
TTY Tx DC Output
Impedance
[1] [3]
R = 2k to
6k
Note: Refer to Annex A for a Non-normative diagram.
RECEIVE
(MS Speaker Output)
TTY Rx Signal Level = -26dBV (nominal) [4]
MS Rx AC
Impedance
Output
MS Rx DC
Impedance
Output
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R  100k
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
TTY Rx AC
Impedance
Input
[1]
Z = 400 to
600
TTY Rx DC
Impedance
Input
R  100k
[1]
Table 1
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Z  150
Notes:
1.) Tolerances: +/- 20%
2.) “AC Coupling” is recommended on all audio outputs. (“DC Blocking” capacitors, etc.)
Refer to Annex B for non-normative clarification.
3.) TTY Output Impedance design goals of pre-2002 devices may not operate at these impedances.
4.) Received audio signal may be –7dBV to –42dBV (refer to Annex A ).
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6. RECOMMENDED “CRITICAL” PHYSICAL PARAMETERS
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“Flush” connections are necessary to allow secure connections.
- Connector assemblies with “Overmold” may not allow flush connections
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“Right Angle” assemblies provide additional strain relief, reducing disconnects.
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Use of connectors that provide a more secure connection by means of an indentation
in the male plug’s tip are preferred over a straight (flat) shaft.
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Cable Shielding: To achieve maximum RFI immunity, the use of a “Braided –
Coaxial” shield wire is recommended. “Spiral wrap” is not adequate. The
recommended material is tinned copper with no silver, (silver acts as a diode
rectifier at 1900MHz.)
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6.1 CRITICAL PHYSICAL DIMENSIONS OF THE 2.5mm
MALE CONNECTION:
(Not drawn to any specific connector manufacturer’s specifications)
1.0mm (max)
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10.3mm (Typical)
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MS
Xmit/MIC
MS
Rcv
Ground
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4.5mm (max)
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Indent for
Positive
Retention
2.5mm
CAUTION: Avoid “Overmold” of the connector housing
that may block secure connection.
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A Right Angle connection cable is recommended for additional “Strain Relief”
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6.2 CRITICAL PHYSICAL DIMENSIONS OF THE 2.5mm
FEMALE CONNECTION:
Preferred: Not Recessed
If Recessed: Clearance and Recess depths are critical
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Recess Clearance
Diameter
6mm (min.)
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Side-Sectional View
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Mounting
Hardware
(nut)
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Recess Depth
1mm (max.)
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Flush or slight protrusion
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Preferred: Flush Plug – Flush Jack
Preferred: Adequate Clearances
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Flush
Connection
Proper
Clearance
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NOT Preferred:
NOT Preferred:
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Female Jack Recess Depth Exceeds 1mm
- Female Jack: Inadequate Recess Diameter
- Male Plug: Excessive Overmold
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Over-mold
Interference
Interference
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NOTES:
 Female connection should not be recessed, to allow the male plug to be fully inserted.
If Recessed
 Recommended clearance diameter is 6mm (min.)
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Recommended maximum recess depth is no greater than 1mm.
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7. INTERCONNECT OPTIONS
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Option 1
Headset Connection
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TTY TERMINAL
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TSB-121
Reference Point
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TTY
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Option 2
TTY Adapter
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(Vendor-Specific)
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NOTES:
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1) The interconnection cable is considered to be part of the TTY.
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2) To avoid a possible interaction with the land network, it is suggested that the TTY’s
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RJ-11 connection to the PSTN should not be used while connected to the wireless
terminal.
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ANNEX A:
(NON-NORMATIVE INFORMATION)
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End-to-End Signal Path
The following illustrations are examples of Infra-structure signal levels expected along
an end-to-end path connection between the two TTY devices.
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Mobile TTY TRANSMIT
Signal Direction:
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TTY- MS
Interface
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RF air
Interface
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Switching
Network
Wireless
Base
Station
(BSC &
MSC)
Mobile
Station
TTY

RJ-11 User
connection
Central Office to
Switching Center
Local
Loop
Line
Loss
Central
Office
(CO)
TTY
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Transmit Level Plan
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At TTY/MS
–20dBV
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CO Output
–10dBm
TTY Input
-20 to –45dBm
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Note: The max signal of –20dBV results in a CO level of –10dBm; providing a 1dB
tolerance to the FCC Part 68 rule of –9dBm max. transmit power into the network.
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Mobile TTY RECEIVE
Signal Direction:
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TTY- MS
Interface
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
RF air
Interface
Switching
Network
Central Office to
Switching Center
RJ-11 User
connection
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TTY
Mobile
Station
Wireless
Base
Station
(BSC &
MSC)
Central
Office
(CO)
Local
Loop
Line
Loss
TTY
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At TTY/MS
–26dBV
Receive Level Plan
At BS/CO
–20dBm
TTY Output
-10 to –12dBm
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Note: At the TTY input from the MS, the tolerance is +14dB to -2dB
utilizing the MS volume control.
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ANNEX B:
(NON-NORMATIVE INFORMATION)
DC Blocking Capacitors in TTY/TDD
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To prevent a DC level conflict between a TTY device and mobile station, as well as for a
mobile station to detect a TTY device properly, the devices should provide DC blocking
capacitors on audio outputs. DC blocking capacitors are commonly used in modern
audio circuitry design, especially for devices powered by separate power sources.
Otherwise, the DC level on one side of the interface may bias the other side to an
undesired level which can cause saturation and distortion.
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TTY/TDD
MOBILE
STATION
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TTY Output
Impedance
MS Input
Impedance
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TIP
To MSMIC
RING
From
MS Spkr
2K - 6K
TTY Input
Impedance
MS Output
Impedance
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SLEEVE
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ANNEX C:
(NON-NORMATIVE INFORMATION)
Hearing Carry over (HCO) and Voice Carry over (VCO)
Both VCO and HCO features are voice communication applications. Therefore, in order
to make both features compatible with standard voice telecommunication products, VCO
and HCO have to meet ROLR and TOLR requirements.
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TOLR = -46dB +/- 5dB @ MRP (mouth reference point) for VCO
+3dB/Pa (Pascal Acoustic) is recommended at Mouth interface Reference Point
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ROLR = +51dB +/- 5dB @ ERP (ear reference point) for HCO
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To simplify the measurement of TOLR and ROLR for TTY/TDD manufacturers; the
following diagrams define the sound pressure level at MRP/ERP vs. the electrical
signal level at TTY-MS interface.
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TOLR
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TTY - MS
Interface
MRP
VCO/HCO
TTY/TDD
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+3 dBPa
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-26 dBV +/- 3 dB
+3 dB/Pa
-26dBV +/-3dB
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ROLR
TTY - MS
Interface
ERP
VCO/HCO
TTY/TDD
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-2 dBPa +/- 3 dB
-26 dBV
-2dB/Pa +/-3dB
-26dBV
These diagrams will give nominal ROLR and TOLR values to meet industrial
standards.
For ROLR, the TTY/TDD vender should also give the user volume controls to allow the
user at least 12dB up without clipping the signal.
For hands-free applications (not including a headset), the measurement should be
done at 30cm from MRP and ERP.
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CHANGE HISTORY
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DATE
June 2001
March- November,
2002
CHANGE COMMENTS
Original TSB-121 published; based on VIF (Vehicle
Interface).
ATIS TTSI requested changes
TR45.1 TSB121 AdHoc formed
 Most signal and impedance parameters changed
 Added TTY Symbol to indicate conformance.
 Show Headset as preferred, most common
 Enhanced graphic examples
 ADD: “Change History” section
Wireless and TTY Contributors to REV-1 of TSB-121
March 2002- November. 2002
TIA TR45.1 Chairman
John Kay – Motorola
[John.Kay@motorola.com]
TSB-121 Editor
Doug Neeley – Nokia
Doug.Neeley@nokia.com
saildoug@yahoo.com
Ameriphone: Alex Lai (Ameriphone/Plantronics)
ATIS:
Jim Turner
Ericsson: Matt Kaltenbach, Steve Coston, Jim Ragsdale
Krown:
Brian Davis
Lucent:
Jane Brownley
Dr.Steve Benno
Motorola: Steven Urbanski
Michael Renner
Nokia:
Daniel Ahlers, Ron Pedigo, Richard Sanders,
Haoye Shen, Ellen Sun, Steve Willhoff
UltraTec: Ron Schultz
Consulting Graphics Artist:
Joyce Neeley CCCC & Univ. Geneseo
Section 1, L-24 . for D.Devaney
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