Instruction manual

ACU-1000 Operations Manual
4-2 Interoperability Now
If the users of one of the radio systems connected to the ACU-1000 regularly miss the initial
syllables of messages from all other radio systems (or other interoperability system members,
such as dispatchers or telephone users), the DSP-2 associated with the system missing the
initial syllables needs to have its TX Audio delay setting increased. A trunked radio system is
the most common and most obvious example of this condition because of the time it takes a
trunked radio to acquire an open channel.
4.2.1 Trunked Channel Acquisition Delay
800 MHz Trunked Radio Systems (and other trunked systems) are a very common public safety
communications format. When trunked system users begin a transmission, their radios must
first communicate with the Trunking Controller. The Trunking Controller has ultimate control
of each radio’s TX function. When a trunked system radio PTT input is activated, the Trunking
Controller first ensures that the user’s radio is on an open channel, and then provides a tone to
the user. This tone signals that it’s now OK to begin speaking. This is an incomplete overview
of Trunked Radio operation, but the concept essential to interoperability is the time gap
between when a user activates a radio’s PTT switch and when that user may begin speaking.
This gap poses a problem to any Interoperability System. When the trunked radio system is
cross-connected to another radio, the operator of the other radio does not hear the “Channel
Ready” acknowledgement tone (also called the “go ahead” tone), and may not even be aware
that he is cross-connected to a trunked system. If this radio operator simply begins talking,
the first syllables or words will be lost while the trunked radio is silent and waiting to acquire
a free channel. This is simply not acceptable in the circumstance when interoperability is most
frequently needed- during a disaster or other unusual event when clear communication is
crucial.
The solution is to add delay to the audio that’s being patched from other radios into the trunked
system by increasing the TX Audio Delay setting of the associated DSP-2 module. This TX
audio delay should match or exceed the channel acquisition time. This holds up the RX audio
from cross-connected radios until the trunked radio is ready to begin transmitting.
Be sure to take into account the fact that channel acquisition times are increased when the
Trunked System is exceptionally busy. Since any type of incident that requires interoperability
is likely to be very busy for all communications, the Interoperability System must have the
ability to add sufficient audio delay to compensate. Keep in mind that the ACU-1000 allows
quick “on-the-fly” adjustment of the delay time either at the incident scene, or remotely using
the ACU Controller or the WAIS Controller.
Refer to Figure 4-1 and Figure 4-2 on the following pages for an illustration of the problem and
how it can be resolved.