Instruction manual

ACU-1000 Operations Manual
Interoperability Now 2-97
how long it takes the module to detect a valid signal in receive audio inputs, plus the time the
radio requires to switch into the RX mode. Keep the sampling window width as short as
possible, because a gap is put into the transmit audio during this time; but not too short or COR
sampling will be ineffective because the system does not have sufficient time to respond. The
factory set value of 150 msec is about the minimum practical value for most radios, while some
radios require a window of 250 msec or more.
2.17.2.8 Noise Reduction Value (DSP only)
The DSP-2 uses time domain mode noise reduction, designed to peak up any correlated
information (such as speech), in the audio passband. It reduces noise by forming dynamic
bandpass filters around correlated information, thus automatically reducing the bandwidth to
the minimum necessary to pass the information. This type of noise reduction is most effective
on purely random noise, such as white or pink noise, and less effective on impulse noises. The
noise reduction value allows the amount of noise reduction to be set in ten steps from off to
maximum. Increasing the level provides more actual noise reduction, but may give a “surging”
quality to the recovered audio depending on its frequency content. Reducing the level lowers
the noise reduction but may provide the best sounding audio in some cases. The best setting in
a particular application depends on the noise level and represents a balance between noise
reduction amount and ultimate audio quality.
The factory default is Off.
2.17.2.9 Audio Muted when Squelched (DSP only)
This selection determines whether the module’s audio output to the ACU-1000 internal bus
(and therefore, to other modules in the system) is muted when the module is not detecting
COR. The default setting mutes the audio when squelched, but sometimes other system
requirements (such as the need for full-time monitoring of an input signal) may dictate the
audio be not muted.
Default setting is muted.
2.17.2.10 Transmit Keying Tones/Keying Tone Amplitudes (DSP Only)
The DSP-2 can mix keying tones with it’s transmit audio output. This allows the DSP-2 to
signal a connected transmitter to key using only the audio output lines, eliminating the need for
an extra wire to carry the PTT output. Keying tone types include a 1950 Hz continuous tone
and the EIA Keying Sequence (see below). Factory default is No Keying Tones.
The Keying Tone Amplitude configuration item command pertains only to the amplitude of the
1950 Hz continuous keying tone relative to the transmit audio output. The selections are 0= -6
dB, 1= -9 dB, 2= -12dB, and 3= -15dB. The default setting is –9 dB.
The DSP-2 can produce the EIA tone keying sequence using function tone F1. The EIA tone
keying sequence has three tones, produced in succession:
• High level Alert Tone, 2175 Hz tone for 125 msec @ +10dB (also called “High Guard
Tone”).