Specifications

BATS AND PORTABLE BATS OPERATION
3-78
sponder will stop replying when the BATS transmitter is turned off, and begin replying when the
transmitter is turned back on, still with erratic ranges. If this is occurring, the operator should
lower the output power of the transmitter by changing the output jumper on the transmitter board,
or increase the transponder's lock-out time and use a longer interrogate interval.
D. Transponder replies accurately (in slant range) , but signals are distorted by mul-
ti-path.
When multi-path is affecting transponder replies, try the following:
1. Lower the hydrophone further from the hull or away from the reflecting object.
Usually multi-path comes from a reflection off the hull or from an object close to the hull and ar-
rives at the hydrophone within one millisecond or two of the direct arrival.
2. Lower the transponder output power.
If changing the threshold does not eliminate the problem, lowering the transponder output, if pos-
sible, may allow the reflected signal to attenuate to a level where it is rejected by the system, but
still receive the direct signal. This is usually only a problem in fresh water where there is less sound
absorption than in sea water.
E. Transponder responds inaccurately (case B or C) and hydrophone receives reflect-
ed signals.
If the operator observes both erratic range and erratic bearing values, the problem is most likely
some combination of multi-path interference, and the operator should try the following:
1. Lower the interrogation repetition rate. In most cases, one signal every three seconds
should give any transmitted or received multi-path bounces time to fade out before the next signal
is initiated.
2. If a slower repetition rate does not solve the problem (or if the repetition rate is already
slower than two or three seconds), the operator should try to isolate the sources of multi-path and
resolve the independent factors using the above guidelines.
F. Transponder responds correctly and hydrophone receives correctly giving accurate
slant ranges but erratic bearings.
This is usually a sign of low signal to noise ratio at the hydrophone. The hydrophone receives the
signal and causes a valid detection but the data processing performed on the wideband signal is
not consistent enough for a bearing calculation. In this case the detected signal is usually flagged
with a low quality factor. To improve Signal to Noise ratio at the hydrophone:
1. Use a “louder” sound source. If the configuration is fixed can a directional beacon with
higher source level be used?
2. Lower the hydrophone to reduce ship radiated noise.