Instruction manual
ACU-1000 Operations Manual
2-106 Interoperability Now
• Interconnecting multiple active PSTNs together on the same net can sometimes cause
hybrid unbalance issues. Please contact the Raytheon factory for further suggestions and
guidance if this is required as there are complex tradeoffs required.
2.17.4 LP-2 Configuration items
2.17.4.1 DTMF Mute Timer
When a module is not in the Data Mode (See Section 3.5.1.9), all DTMF signals detected in the
receive audio are interpreted as commands meant for the receiving module. When the DTMF
Mute Timer is enabled, the DTMF command signals are “Muted”; that is, they are not passed
on to the ACU-1000 internal audio bus to be routed to another module, nor are they sent back
out in any module’s TX audio. A module cannot instantaneously mute a DTMF signal; some
time is required to detect its presence. Therefore, when a DTMF signal first becomes present in
the receive audio, a short burst is passed through. The DTMF mute timer ensures, if a long
string of DTMF characters are present in the receive input, a short burst of only the first DTMF
character is passed through. This is accomplished by muting the audio as soon as the first
character is detected, and then keeping the audio muted until the first character is complete, and
until enough of the next character has been received so it is detected. Each time a new DTMF
character is detected, the timer is reset. When the timer expires (because no new DTMF
character is detected in the receive input), the audio is no longer muted.
The factory default is DTMF Mute Timer Disabled, as the majority of ACU-1000 systems do
not employ DTMF control. This setting allows the DTMF signals to be passed through the
system like all other audio. It also prevents inevitable occasional “falsing” on voice signals that
are similar to a DTMF character; this falsing would momentarily mute throughput audio.
If DTMF control is used, it may be desirable to mute the DTMF characters as they may be
annoying to other system users, and a timer setting 1 second works well in most cases. If the
setting is too low (because some system users transmit DTMF characters slowly), a short burst
of DTMF will be passed through at the start of each DTMF character. The timer should be set
to a value that is longer than the maximum time elapsed between the end of one DTMF
character and the start of the next.
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).
2.17.4.1.1 Transmitting DTMF via a PSTN Module
If the system will be used, for example, to allow a local phone user to control a telephone
answering machine via DTMF, the following will occur:
A local phone with a DTMF keypad will send DTMF characters to an associated LP module.
This LP module will be cross-connected to a PSTN module that is hooked to a phone line. If
the local phone user creates the cross-connection using the DTMF keypad, the LP module must
be in the Command Mode when he does so. He must then use the keypad to put the LP module
into the Data Mode. When in the Command mode, DTMF coming into the LP module is
interpreted as system command input. When in the Data Mode, the incoming DTMF is