Instruction manual

ACU-1000 Operations Manual
Interoperability Now 2-93
2.17.2.6 COR Type, VOX/VMR Threshold, Hangtime, and Audio Delay (DSP Only)
The DSP-2 and RDI-1 modules must have positive knowledge an input audio signal is present
so they know when to key an associated transmitter. A signal that provides this information is
called COR (for Carrier Operated Relay, sometimes referred to as COS Carrier Operated
Squelch). The RDI-1 can handle hardwire COR signals only, but the DSP-2 module can use an
external hardwire COR line, an internal VMR (Voice Modulation Recognition) algorithm, or a
VOX Squelch. In a full duplex connection, it may be desirable to ignore COR activity
altogether and never mute the incoming audio. The correct selections depend on the type of
radio or other equipment that is connected to the DSP-2 receive audio input.
• FM Radios- For best reliability, use a hardwire COR signal, if one is available from the
radio’s own squelch circuit. If no hardwire COR signal is available, and the radio has a
squelch circuit, use the radio’s squelch in conjunction with VOX mode. VMR should be
used for FM radios that must be operated with an open squelch (receiver noise is present
when there is no signal). The VOX cannot be used in this condition because it will open on
receiver noise, but the VMR opens only on speech, not on receiver noise. When used in
this mode, the VMR threshold must be set to Med2 or High to avoid falsing on white noise
from the FM discriminator.
• AM Aircraft Radios- Again, the best choice is a hardwire COR line from the radio, if one
is available. If this isn’t an option, VMR should be used. VMR thresholds of Low or Med1
may be most appropriate for this application.
• HF SSB Radios- The only reliable choice for HF radios is VMR. VMR thresholds of Low
or Med1 may be most appropriate for this application.
• Non-Radio Applications- The choice for these applications is hardwire COR, if this signal
is available. If not, use VOX if the audio is relatively noise-free; use VMR for noisy
signals.
Whenever VMR or VOX are selected, the DSP-2 will switch to default audio delay and
hangtime settings that work well for each of these COR types. These default settings are
recommended, but not mandatory except as explained below. When VMR or VOX is selected,
the defaults are set. The user may then make a change in these settings if any are necessary.
The Audio Muted When Squelched configuration item may be turned off so the module ignores
COR and does not mute incoming audio when COR is active. This may be desirable for full-
duplex setups. Disable muting when using the HSP-2A to monitor a module or group of
modules.
To set up the DSP-2 for best operation with each of the COR choices:
• Hardwire COR- The only parameter that needs to be set is the COR polarity. If the radio’s
COR output goes low when a signal is being received, set the input to active low; if the
radio’s COR output goes high when a signal is being received, set the input to active high.
• VOX- The VOX algorithm will signal COR present whenever the incoming audio exceeds
a set threshold. The signal can be tones, voice or noise. The VOX algorithm is looking for
any audio signal above the set threshold. Three parameters determine how the VOX