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SINGLE-PING ECHO-RANGING |
If the conning officer requires a range more accurate than his periscope
can give, he may order, "QB, get a single-ping range." The sonar operator
then aims his projector at the target and shoots out a single burst of supersonic sound called a ping. The time until the echo returns gives a measure
of the target's range. There will be a series of small echoes, called reverberations, but the clear note of the main echo from the target can generally be distinguished.
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This requires two additional units of
equipment, different from those which
have been discussed so far.
The Driver sends a pulse of current
of supersonic frequency to the projector, which projects a ping into the
water. There are two drivers, both located in the forward torpedo room. One
is connected to the QB projector; the
other is used with either the QC projector (echo-ranging) or the NM projector (echo-sounding to get the depth
of water beneath the keel).
The Range Indicator is a giant electric stop-watch which measures the
time between the ping and the return
of the echo. Its dial is marked off in
yards so that the range can be read
directly.
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WCA, WCA-1, and WCA-2 Range Indicators
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WCA and WCA-1
The black panel containing four screw
driver adjustments appears only on WCA
and WCA-1 range indicators. Power can
be obtained from a generator or from the
ship's AC.
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WCA-2
In WCA-2 the screwdriver adjustments
have been replaced by hand switches.
There are no generator buttons because
this model operates entirely on ship's AC.
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Advantages of QB for single-ping echo-ranging
Although either QB or QC can be used to get a single-ping range, QB
is better for several reasons:
1. You are more certain of getting a good range on a single ping. Although both send out about the same strength of sound, QB can pick up a weaker echo.
2. You do not have to be so exact in setting the tuning dial when using
QB. With QC, it is necessary to tune to an exact frequency.
3. If you have been using JK for listening, before you can use QC, it
is necessary to turn the input switch to QC and train the QC bug halfway
around the bearing circle. With QB you are ready to ping instantly.
QC must be used when the target bears between 250 degrees and 290 degrees relative.
At these bearings the QB projector is blanked out by the JK/QC projector,
which is then between it and the target.
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How to set the controls for a single-ping range on QB
On the QB receiver-amplifier
1. Use the frequency on which you have been listening, which should be
about 28 kc, because you have raised the tuning to narrow the target.
2. Be sure filters are on BROAD-FLAT.
3. Be sure the driver-power switch is on HIGH.
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How to set the controls for a single-ping range on QC
On the QC receiver-amplifier
1. Turn input switch to QC. Train the projector through half a circle
so that the QC bug is on the bearing of the target.
2. Tune exactly to the frequency written above the tuning dial. Very
accurate tuning is extremely important.
3. Be sure filters are on BROAD-FLAT.
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How to get a single-ping range
by the audible method
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1. Train the bug 2 degrees toward, the target's
bow from the bearing where the sound
is loudest. Turn the gain down to protect your ears.
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2. Just before the white light slit reaches
zero, move the switch to AUDIBLE,
keeping one hand on this switch.
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3. When the slit has passed 300 yards, return the gain to its former level in order
to get a louder echo.
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4. Keep your eyes on the revolving slit and
listen intently for the echo. Disregard
the rolling reverberations, and concentrate on catching the clear note of the
returning echo from the target. At the
instant it comes, note the reading on the
scale. This is the range.
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5. When the slit reaches 4000 yards, return
the switch to MANUAL KEYING.
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When and how to use the visual method
Sometimes when your submarine is within 1500 yards of the target, the
visual method may be used instead of the audible method. This requires two
changes:
1. Instead of setting the switch at AUDIBLE, above it to VISUAL.
2. When the light slit arrives at zero, an arc of red light will flash, indicating that the ping is going out. Following this there will usually be a
series of little red flashes caused by the reverberations. Then a good solid red
flash will come at the same time that you hear the target echo. Read the
range at the trailing edge of this flash.
This visual method involves two serious dangers. First, if the gain on
the receiver-amplifier is set too high, you will get a confusing series of red
flashes all over the dial from the reverberations. Second, to flash the red light
requires more current than to produce an echo in the headphones; so you are
likely to get no flash at all from a weak echo.
Why submarines do not echo-range continuously
Since the speed of surface escort ships produces a noise level too high
for efficient listening, they depend heavily on echo-ranging to detect submarines. In fact, surface escorts echo-range continuously. But submarines hardly
ever echo-range, because a submarine has to keep its location secret from the
enemy. Continuous pinging would be a dead giveaway.
When the submarine conning officer needs a sonar range, he allows the
operator only a single ping. For the submarine's purpose a successful single
ping range is sufficient -- and it's fairly safe.
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