Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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This invention relates to an electronic interface for
use with a mobile radio transceiver as part of a telephone
network to permit transmission and automatic/manual
reception of both voice and analog data information.
This interface accommodates units normally connected
to standard telephone land line networks such as telephone
units, cordless telephones, answering machines, facsimiles,
computer modems, etc.
Both simplex and duplex radio transceivers make up the
family of mobile radios. The interface accommodates these
various styles of radio transceivers using MTS, IMTS,
*NOVATEL 400 MHZ Cellular and the 800 MHZ Cellular.
Mobile radio units are used extensively in remote
areas in which conventional telephone lines are not
available. Frequently, for example, oil wells are located
in areas which are not serviced by the telephone network.
The rapidly expanding field of communication by data
transmission means such as facsimile and computer modems
have made available to surveyors, oil drilling operators,
etc., a valuable tool in providing instantaneous
information from one site to another. The lack of a
telephone system to remote areas has limited the efficiency
of this data transmission process.
In Canadian Patent 1,223,059 which issued June 16,
1987 to Polanski Electronics Limited, there is disclosed an
interface to permit transmission of signals between a data
transfer unit and a radio transceiver. The 1,223,059
patent discloses an interface having a receiving circuit
and a transmitting circuit, an analog data bus to transfer
data between the device and the circuits and a switch to
connect either the receive circuit or the transmit circuit
to the device.
The present invention overcomes the requirement of the
switch means by having both the receive and transmit
circuits operationally connected between the device and the
radio. The device of the present invention further provides
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a selectlon mode whereby the caller may dlrect the lnterface
unlt to couple the radlo to one or more receive units such as
a facslmlle unlt, answering machlne or computer modem. The
present interface also allow~ for the un-attended reception
of an lncoming radlo call to an answering machine or a data
devlce. Presently, incoming calls must be answered by the
radlo user to accept the call and to manually acti.vate any
devlces connected, such as facslmiles. After data completlon
the operator would then have to place the radio on-hook. The
1~ devlce of the present invention further provides loop current
for detectlon of a load on either port to connect that unit
to the receive and transmit circuits of the lnterface. This
elimlnates the need for manually switching from VOICE TO DATA
to connect the device. Control of the selection means is
performed by the sender by transmitting a code, such as a
selected keypad on a telephone to make the appropriate
selectlon. In the transmit mode, the call is placed as in
normal radlo operatlon and when contact with the unit at the
answering end is completed, the facslmile or modem is
connected for normal transmission. Therefore, in accordance
wlth the pre~ent lnvention, there is provlded an interface
means for use with a mo~lle radio to permit the radio to
receive and transmlt data and voice information, the inter-
face means includes connector means for connectlng the
interface to the radio, port select means including means to
selectlvely couple the interface means to one or more means
to recelve or transmlt data and voice information, converter
means adapted to interconnect the connector means to the port
select means, circult means responsive to a receive single
3~ from the radlo operable to select receive data information
means coupled to the port select means, circuit means
respons~ve to transmit signals from the transmit information
means to operate the radlo in a transmit mode, and a power
supply to provide operating power to the interface.
The preferred embodiment of the present invention will
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now be descrlbed in greater detail with reference to the
appended figures whereln:
Flgure 1 is an overall system ~lock diagram;
Figure 2 is a block dlagram of the interface of the
present lnven~ion;
Figure 3 is an illustration of the radio connections;
Flgure 4 illustrates the 2 to 4 wlre converter;
Figure 5 is a flow chart of the lnterface logic;
Figure 6 lS a clrcuit dlagram of the inter~ace power
supply; and,
FlgUre 7 lS a circult dlagram of the interface logic
board.
Referring in1tlally to Figure 1, there is illustrated,
in block form, the overall relationship of the components o~
the system according to the present invention. It is assumed
that within the operat1on of the telephone company 10, there
is a mobile radio facility including a mobile radio operator
12. Many of the present mobile radio systems rely on a
central operator to intercept and pass through calls orlgin-
atlng from a remote station, and in those cases, the systemo~ the present invention also relies on the mobile operator.
A standard land line telephone system 14 links the telephone
company 10 to the main office or base station 16. The mobile
unit 24 i~ located at a remote station 18 without normal
telephone servlce. Calls originating from the mobile radio
are transmitted from the mobile's antennae 20 to the trans-
mlssion tower 22 and, hence, to the mobile operator 12. On
some simplex and duplex radio systems there is no telephone
operator required to ass1st in placing calls to or from a
mobile radlo, such as in cellular radio. The present
interface will transmlt and receive data without -the neces-
slty o~ the telephone operator intervention.
The mobile station 18 as shown in the block d1agram
includes the mobile radio 24 with antennae 20, the interface
26, which is the subject of the present invention, and a
facs1mlle machlne 2~ and/or an an~wering machine 30. It is
al~o w1thin the scope of this lnvention that the interface
unit 26 may be connected to a computer modem ~not shown) and
other such devlces whlch may be connected to a telephone
unit.
When the mob1le radlo 24 is to be used as a facsimlle
sendlng devlce, normal radio connectlon is made to the mobile
operator 12 who, ln turn, patches the call through to the
telephone ln the base statlon 16. When contact has been
completed wlth the base station telephone, the interface unit
26 is actlvated by the operator and the facsimile message is
transmitted through the system in an analogous manner to
messages whlch are transmitted over a land line telephone
system. Slnce communicat1on to the base station may require
the asslstance of the mobile operator, it is not possible in
tho~e cases for the present system to program -the facsimlle
machine to automatlcally send or transmit data information.
The system, however, does permit automatic and unat-
tended reception of audio messages or data transmissions.
The call orIg1nator at the base off1ce 16 makes contact by
telephone to the mobile operator 12 who then patches the call
through to the mobile radlo 24 in the normal manner. The
mob1le radlo 24 receives the telephone ring signal and,
provid1ng the lnterface 26 lS powered on and the facsimile
unit 28 and answering machlne 30 are on hook, the interface
will connect the lncoming call to PORT A. If the operator of
the radlo transceiver wishes to leave a recorded message the
interface 26 may be set up to have the answering unit 30
answer automatlcally to recelve the call and in turn, provide
the caller with a recorded message. The interface 26 may
also be programmed to have the answerlng machine 30 automati-
cally recelve the call and to, in turn, provide the caller
Wl th a recorded message as to the proper procedures to follow
in sending the facsimile transmission. This instruction
could be that pressing # 8 on the caller's touch-tone phone
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would actlvate the facslmile ln PORT B ~o connect to the
transcelver for facslmlle data trans~er.
The overall systern wlll now be descrlbed in greater
detail wlth reference to the lnterface block diagram shown in
Flgure 2.
The radio connectlon sectlon 40 includes a multi pin
connector whlch provides all necessary connections. Figure 3
lllustrates the relatlonship between a conventional radio
connector and the connections to the interface unlt.
Tne audlo receive signal 46 from the radlo and the
transmit signal 48 to the radio pass from the connector to
the two-to-four wlre converter 50 b~ way of an audio buffer
44. The audio buffer provides gain control on the receive
path to ad~ust the incoming signal to an optimum level at the
input to the facslmile machine. The audio buffer 44 also
includes means to adjust the transmit level in order to
accommodate differlng levels required for different radios.
This adjustment lS set by the installer according to specifi-
cations. The audio buffer 44 also includes operational
2~ ampliflers to reject power supply noise in order to aid in
nolse reduction. The receive and transmit signals are fed to
the two-to-four wire converter 50 which converts the separate
receive and transmit paths of the radio to the single two
wire path of a standard telephone. The converter design is
based on a subscriber loop interface circuit 52 (SLIC) which
is available from manufacturers in the form of an integrated
circuit requiring only a few auxiliary components. The
converter performs the functions of telephone hook switch
detection, ring relay driving, and two-to-four wire conver-
sion. The two-to-four wire converter is shown in greater
detail in the block diagram of Figure 4.
In Figure 4, the balance circuit 54 associated with the
SLIC is required to provide an impedance match between the
interface and the telephone equipment. This is a simple R-C
network. The converter must provide suffic1ent channel
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separation and compensation such that receive signals do not
get retransmitted causing erroneous activations of the voice
activated circuit.
Transient protection 56 on the telephone side is
required to protect the interface from inductive switching
spikes. This will be in the form of flyback diodes with
performance equivalent to a *Motorola MDA 220/210G.
The ring relay 58 is controlled by the SLIC 52 which, in
turn, is controlled by the logic section 70 to be described
hereinafter. The ring relay 58 switches the telephone feed
between normal loop voltage and the ringing voltage. An
important function of the SLIC 52 is to switch off the
ringing voltage when the telephone service goes off hook.
Returning to Figure 2, the port select relay and driver
60 is a simple double pole/double throw switch that connects
either PORT A or PORT B to the two-to-four wire converter
50. The port selection command is a logic level signal from
the logic section 70. If necessary, this logic signal could
be boosted by a relay driver to give adequate current drive
to the relay coil 58. The relay must be chosen to withstand
the ringing and switching voltages on the telephone interface
and the shock and vibration of the mobile environment.
The power supply 80 is designed to provide sufficient
loop voltage and loop current to operate the system. The
loop voltage i5 generated using a switching power supply.
The ring generator 82 requires a minimum voltage of 50 volts
RMS superimposed on the loop voltage. The ringing voltage is
a rough sine-wave at typically 2OHZ. It can vary peak-peak
with a nominal voltage of 60 volts p.p. The voltage of the
rails will be chosen to give a -48 volt plus or minus 6 volt
DC offset.
The VOX circuit 90 detects transmitted levels from both
the facsimile and the answering machine connected to PORT A
or PORT B. Levels greater than a threshold cause the push to
talk button on the radio to be activated. Any audio level
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a~ove the threshold lnput triggers the push to talk on the
rad1o. The c1rcult has an adjustment for minimum on time
(nom1nally 2 seconds) and a separate adjustment for turn off
tlme tafter the on time has expired - nominally 0 2 seconds)
us1ng flxed res1stors. The threshold is adjustable by the
installer.
The call and tone detector l00 sets a call alert signal
102 to a loglc high when the received audio level reaches a
factory set threshold while the selected port is on hook.
Call detect1on is performed using an op amp comparator with a
filtered output to reject spurious response. The tone
detector sets a tone detected s1gnal 104 to a logic high when
a part1cular frequency is detected in the received audio.
The specif lC frequency used is chosen for ease of implementa-
t1on in the absence of other operational considerations.
The logic section 70 controls the operation of the
elements within the interface unit. The logic section
follows the protocol shown in the interface logic flow chart
of Figure 5. The control panel ll0 allows the operator to
manually reset or power off/on the interface. The control
panel also contains visual indicators in the form of LEDs to
indicate to the operator the status of the operation.
For greater detail with respect to the interface circuit
and the power supply, reference may be made to the detailed
circuit diagrams shown in Figures 6 and 7.
For operation of a call originating from the facsimile,
the interface unit can be powered off or on. The call is
established in the conventional manner using the mobile radio
including confirmation that another facsimile machine is
3~ connected at the base station. At power-up PORT A is
selected by default and at the end of every call handled by
the interface, the unit automatically returns to a PORT A
select. It is to be understood that either PORT A or PORT B
can accommodate either a facsimile unit, an answering machine
or a computer modem. The port required for the send opera-
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tlon is selected by the activation of the unit connected tothat port. The fac~lmile unlt lS thus operated in the manual
mode. When the facslmile unit goes off hook, the radio
cradle switch is activated (regardless of whether the handset
is in the cradle or not), and the radlo handset is usually
dlsabled, and the microphone insulated as not to transmit
induced nolse onto the transmit data. This may vary depend-
lng on the style of radio. The audio circuits are then
automatically dlverted to -the interface, and data transmis-
sion can commence. The voice activated switch (VOX circuit)detects the presence of a transmit audio signal and controls
the push to talk input to the radio accordingly.
Upon completion of the facsimile transmission, the
facslmile unit automatically hangs up or goes on hook. At
this time, the interface unit can be turned off if desired by
the operator and the radio is enabled for conventional use.
Incoming calls may be received in either manual mode or
automatic mode. In manual mode, incoming calls for conversa-
tion can be handled in the normal manner through the handset,
providing that the loop interface is not powered up. If the
interface is powered up, it will ring the selected port when
an incoming call is detected. The device on that port may
answer the call before the user and i it does, the radio's
handset may be disabled. In this instance, -the user can then
either disable the interface and use the radio in the
conventional method or allow the device to operate and handle
the call automatically.
For automatic reception, the interface unit is powered
up and both ports are in the on hook condition. An incoming
call generates a tone on the speaker, and when the interface
detects this tone, the ringing process is initiated on the
selected port. As indicated previously, PORT A is selected
by default at power up and at the end of each call handled by
the lnterface. If the selected port does not answer (go off
hook) within several rings (7), the interface selects PORT A
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and returns to the ready state. If the selected port goes
off hook, the radlo cradle switch is actlvated (regardless of
whether the handset is in the cradle or not), the radio
handset is usually disabled, the audio circuits are automati-
cally diverted to the interface and transmission can com-
mence. Once the call has been established to the selected
port, the calling party can select the other port by pushing
a selected digit, for example, keypad # 8 on the touch tone
phone. Upon reception of that tone, the interface switches
to the other port and restarts the ringing process. If the
other port does not answer within five rings, the call is
terminated, PORT A is selected, and the interface returns to
the ready state. This provision for switching ports remotely
has been implemented so that an answering machine can perform
its usual function of transmitting and receiving messages,
and also ~o instruct the caller on how to leave a facsimile
message. Thus, both a voice and facsimile message can be
left during the same incoming call.
~lthough the foregoing description has been directed
primarily to facsimile units and answering machines, it is to
be understood that the interface can be programmed to access
a computer modem connected to either port. It is also within
the scope of the invention to provide more than two ports
such that a facsimile unit, an answering machine and a
computer modem and other analog data or voice devices
normally assoclated with telephone networks can be connected
to the interface unit and, hence, accessible by the mobile
radio. For example, a cordless phone has been tested on the
interface and it adds extra features to the interface
systems. It allows a remote answer capability to the radio
if, the caller is physically away from the radio. The system
is limited mainly by the working range of the cordless phone.
On some radio transceivers, placing a call is also available
through the cordless phone.
Also, an answering machine that can be accessed by a
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remote beeper can offer the operator a system which he/she
can retrleve their message by calling their own radio and
after the answerlng machine answers activate their remote
beeper.
While there has been shown and described a preferred
embodiment of the invention, it will be appreciated that
various modifications and adaptations of the invention will
become readily apparent to those skilled in the art and it is
intended that such obvious modifications and adaptation be
1~ encompassed Wl thin the claims appended hereto.
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