Specifications

BATS AND PORTABLE BATS OPERATION
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3.6 TROUBLESHOOTING ACOUSTIC PROBLEMS
3.6.1 TRANSPONDER MODE
A transponder emits an acoustic signal of a known frequency in response to an acoustic interroga-
tion pulse sent from the BATS Transceiver. The primary advantage of using a transponder is that
the target range can be measured directly from the round-trip travel time of the acoustic signals.
A transponder, therefore, is NOT subject to the "cone of operation" limitation that applies when a
pinger is used.
A potential (minor) disadvantage in using a transponder (over a responder) is that both the inter-
rogate pulse and the transponder's response may be subject to multi-path.
A high noise and/or multi-path environment may cause any of the following situations:
A. Transponder cannot "hear" interrogate pulse.
In an extremely noisy environment, it may be impossible for the transponder to distinguish an in-
terrogate pulse in the noise flooding its receivers. In the worst case, the transponder simply won't
reply, and is essentially lost for tracking purposes. A pinger or responder is a better choice for
such an environment.
B. Transponder accepts noise or extraneous signals at the correct interrogate fre-
quency.
In this case, transponder replies will be random and uncoordinated with the interrogate pulses.
The operator may observe correct bearing information although range is random and incorrect. To
determine whether this is the case, turn the BATS Transceiver transmitter off and observe whether
the transponder is still replying. If it is, the operator should try to identify and eliminate the source
of the false interrogate signal or noise. If the source cannot be eliminated, it is necessary to
change the interrogate frequency, or switch to pinger or responder operation, or possibly reduce
the sensitivity or frequency of the transponder receiver. It is also possible that there is an interfer-
ence signal from some other sound source that is the multiple of the Multibeacon frequency caus-
ing the detection rather than the Multibeacon triggering on noise. If it is another sound source then
it usually is of a repetitive nature, whereas if the Multibeacon is triggering on noise the detection is
more random.
C. Reflected interrogate signals cause extra transponder replies.
Most transponders are designed with a 'lock-out' (usually 1.5 - 1.75 seconds), or limit on the rate
at which the transponder can reply, to prevent this from occurring. The operator should be aware
of such a limitation, so that he does not interrogate at a rate too fast for the transponder.
In rare circumstances, the transponder can be replying to a distant reflection of the interrogate
signal in addition to the direct signal. (The reflected signal comes in after the lock-out.) If this is
the case, the operator observes correct bearing values with erratic ranges as above, but the tran-