Instruction manual

ACU-1000 Operations Manual
2-92 Interoperability Now
There are some circumstances when it’s important that incoming DTMF not be interpreted by
the ACU-1000 as control input, but instead must be passed to other equipment. The settings
used are different depending on whether the module that’s passing on the DTMF is a PSTN-2
module (which regenerates DTMF) or any other type of module (which do not).
2.17.2.5.1 Transmitting DTMF via a PSTN Module
If the system will be used, for example, to allow a radio user to control a telephone answering
machine via DTMF, the following will occur:
A radio with a DTMF keypad will transmit to a radio wired to a DSP-2 module. This DSP-2
will be cross-connected to a PSTN-2 module that is hooked to a phone line. If the radio user
creates the cross-connection using the DTMF keypad, the DSP-2 module must be in the
Command Mode when he does so. He must then use the keypad to put the DSP-2 module into
the Data Mode. When in the Command mode, DTMF coming into the DSP-2 module is
interpreted as system command input. When in the Data Mode, the incoming DTMF is
interpreted as control characters intended for other equipment and all DTMF (other than the
DTMF sequence that signals the module to return to the command mode) is not interpreted as
control commands. See Section 3.5.1.9 for more information about the Command and Data
Modes.
While in the Data Mode, the DTMF from the radio is detected by the DSP-2 module and
relayed via the CPM-4 module to the cross-connected PSTN-2 module as serial data. The
PSTN-2 regenerates and transmits the DTMF characters into the phone line. This Data Mode
regeneration cleans up the DTMF, so any noise or frequency-response related distortion of the
DTMF characters (caused by radio transmission of the DTMF) is not passed on to the phone
line.
When the system is used in this way, the DSP-2 module should have its DTMF Mute Timer
turned on, so that only the regenerated DTMF will be sent via the phone line.
2.17.2.5.2 Transmitting DTMF via a Module other than the PSTN-2
If it is desired that DTMF characters be passed through the system, being sent out by a module
other than a PSTN-2, the DTMF mute timer must be turned off. This is required because only
the PSTN-2 regenerates DTMF; the others will just pass it through like any other program
audio. The DTMF mute timer must be set to off on the module that receives the DTMF or it
cannot be passed on to the cross-connected module or modules.
Please note that it is possible, but not advisable, to retransmit DTMF, bringing DTMF into the
ACU-1000 on one radio via a DSP-2 module and then retransmitting the DTMF on a second
radio via a cross-connected DSP-2 module. The normal FM noise that will accompany the
DTMF, along with frequency response related distortion (caused by pre-emphasis & de-
emphasis in the radio audio circuits) may have an adverse affect on DTMF signal quality and
detection.
Since the majority of systems do not use DTMF signaling, the factory default sets the module
with the DTMF Mute timer turned off.