Klein 3900 Series Operation And Maintenance Manual page 24

1-6
CHAPTER 1 Overview
The two transducer arrays are each composed of piezoelectric ceramic sub-arrays
that operate as both transmit and receive elements. Each set of sub-arrays is
arranged into a continuous line array spanning an overall aperture of
48 centimeters.
The towfish electronics is divided into four individual boards: a 900 kHz
Transceiver board, a 445 kHz Transceiver board, a Power Supply board, and a
Multiplexer board. A block diagram of the towfish is shown in Figure 1-3.
445 kHz and 900 kHz Transceiver boards.
Transceiver boards each include a transmitter which produces a transmit pulse,
at the start of a swath, that illuminates the sea floor over a defined footprint.
The pulse length is adjustable for both the 445 kHz and 900 kHz channels. For
the 445 kHz channel the selections are 16, 25, 32, and 100 µs. For the 900 kHz
channel the selections are 8, 20, 60, and 100 µs. The transmitters are connected
to both the port and starboard transducer sub-arrays, and they operate at a
center frequency of 445 kHz. The transmitters are Class-D switching types
coupled through a double tuned transformer to the transducer sub-arrays.
The 445 kHz and 900 kHz Transceiver boards each include a receiver which
processes the backscatter information by applying fixed gain, time varied gain
(TVG) and frequency filtering to the input voltage signals received from the
individual sub-arrays in the transducer arrays.
The receivers first process the transducer data by isolating the input
preamplifier electronics from the high voltage transmit signal via a
transmit/receive (T/R) switch. The T/R switch is automatic and requires no
intelligent control. After the transmit waveform has decayed, the switch closes
to allow the receive signals to enter a fixed gain low noise preamplifier stage.
The output of the preamplifier is input to a voltage controlled amplifier (VCA)
which performs the TVG function. The gain versus time relationship, TVG,
that is applied identically to all channels is digitally synthesized from a
predefined curve stored in a PROM on the Multiplexer board. Provision has
been made for the storage of alternate TVG curves but in practice it has been
found that the use of these has been limited to test procedures.
Series 3900 Sonar System Operations and Maintenance Manual
NOTE The transducers are side specific and are not interchangeable.
The 445 kHz and 900 kHz
11214510, Rev. 02