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Maintenance
ANALOG TRANSCEIVER: BOARD
Functional description
The analog transceiver board , split beam , contains a four-channel
transmitter
and a four-channel receiver. The transducer is
connected to the board through
plug P3. The board operates together with the digital transceiver board which
digitizes amplitude and phase data to a format suitable for
microprocessing.
The single-
beam version of this board is identical to the split-
beam version
except that it only contains a one-channel
transmitter and receiver
, and has no
outputs for phase information.
Transmitter
Refer to the lower part of Figure
9. The transmitter is controlled by two TTL-
signals , the trigger
signal
TXI
and the signal 2xfo which decides the trans-
mitter frequency
fa. Both signals are generated on the PC interface board
, and
are dependent on transmitter frequency
and menu settings. The transmitter
has one transformer with four outputs.
While receiving, the four channels
are
separated by anti- parallelled diodes. The transmitter has built- in short- circuit
protection and has also a fuse in front for battery short- circuit protection
The TX-
pulse is indicated by the LED across the transformer primary (located
for easy
viewing on the front of the
board). The transmitter
power can be
halved by mounting link A instead of link B on
the transformer primary
side.
There are four separate output
channels.
Receiver
Refer to the upper part of Figure
9. The receiver has four separate
receiver
inputs
, one from each of the transducer
elements. It has a
TR-switch which
protects the receiver while transmitting, and it can
take an amplitude of 5
volts RMS before it saturates. The gain over the
input filter is about 16
dB and
another 14 dB
comes in the
following transistor network. The next amplifier
stage is a low-noise op amp and
gives about 30 dB gain. The next amplifier
stage gives also about 30 dB gain and it
includes a low-
Q bandpass filter as
well.
At the end of each channel there is a precision comparator with a TTL-output
which goes to the phase detector at the digital transceiver board. The input of
the comparator
is saturation protected with
a voltage divider. The supply
voltage to the comparators
comes from separate voltage regulators because of
noise considerations.
The four TTL outputs
represent relative phase angles.
P3405E/B
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