ARA-1 Operations Manual
5-6
INTEROPERABILITY NOW
5.7
Ping Pong
“Ping Pong” is a descriptive term for a very disruptive behavior that some types of radios exhibit:
when cross-connected (conferenced within a SIP PBX); each causes the other to repeatedly key
momentarily. The full activity may be difficult to diagnose when the radios are cross-connected
a large distance apart over a network (allowing only one radio to be seen at a time), but the one
visible radio will repeatedly key momentarily. The ARA-1 has a configuration feature that can
prevent this disruptive behavior.
The root cause is the tendency of some radios to inappropriately unsquelch momentarily at the
end of each transmission. That is, a radio receives a PTT input, putting it into the transmit mode,
and when the PTT input ends, the radio not only drops out of the transmit mode but jumps
momentarily to the unsquelched receive mode, even though there is no external RF input to cause
the radio to unsquelch.
Remember that for any pair of cross-connected radios, whenever one radio is unsquelched, the
other is keyed. If a radio of the pair exhibits the “momentary inappropriate unsquelch after PTT”
behavior, any cross-connected radio will momentarily (and inappropriately) transmit. If both
radios unsquelch momentarily at the end of each transmission, the system will repeatedly “ping
pong,” with first one radio keyed momentarily and then the other.
This effect can be experienced when the PTT inputs are activated by either a COR input or by
VOX (as some radios will send out a noise burst after they unkey).
To prevent this, first use the ARA-1 front panel LEDs to determine if the particular radio make
and model connected to the ARA-1 exhibits the “inappropriate COR after PTT” behavior. The
Channel Active LED lights whenever the ARA-1 is detecting active COR. During the system
configuration process, simply observe this LED after the radio keys. If it flashes on momentarily
at the end of each key sequence, turn on the adjustable
Radio COR Inhibit Time
(see Section
3.3.1) and increase the time value until the condition no longer occurs. This function instructs
the module to ignore any unsquelch detection (COR) that occurs immediately following the
cessation of a transmit sequence. The duration of the timer is adjustable to optimize for different
radios, which may exhibit the inappropriate unsquelch indication for times as short as 100
milliseconds, and as long as several seconds.
5.8
False Keying
The ARA-1 has a feature to prevent the radio cabled to the ARA-1 from keying up frequently
(that is, going into TX mode) due to background noise coming in on the network audio (for
example, from connected SIP Phones in high-noise locations or multiple SIP Phone users all
conferenced together, with one or two users breathing heavily while they are supposed to be just
listening). The ARA-1’s
Network COR Type
can be switched to
VMR
mode. VMR stands for
Voice Modulation Recognition; with this mode enabled, the radio will key only if there is actual
speech detected in the audio from the network.
End of Section 5