Introduction; Logic Circuit Symbols; Normal Mode; Signal Input - Racal Instruments 9916 Workshop Manual

INTRODUCTION
4. 1 Apart from some switches and certain items of the power ,supply the circuit for
the instrument is mounted on one main p.c.b. assembly, with smaller assemblies
for the display, the frequency standard, and the LF Mul tipl ier and Battery Power Supply
options.
LOGIC CIRCUIT SYMBOLS
4.2 Extensive use is made of integrated circuits (ICs). These are identified by a
number and suffix letter.
In
the circuit description a particular IC pin will be
identified by a reference such as IICl0/2
1
/
which indicates pin 2 on that particular gate.
The logic sysmbols used
in
the circuits are those found in most manufacturers IC data sheets,
to which reference should be made if detailed information is required. The CDI chip lC4
is, however, obtainable only through the Service Department of Racal-Dana Instruments Ltd.
NORMAL MODE
Signal Input
4.3 Two input channels, designated 'A' and
'B',
cover the full frequency range of the
instrument. Separate input sockets are provided. Details of the frequency
coverage are given in the Technical Specification.
I
A' Channel Ampl ifier
4.4 The signal to be measured is applied to the front panel HNC socket SK51, and
passes via C36 and the contact of the overload relay RLA-1 to the AGC attenuator.
This is a PIN diode network, D11, D12, D13, D14 and D15.
4.5
The signal leaving the attenuator is amplified in a wideband VHF amplifier
IC26 and a transistor stage 09. It is then passed via C50
to
the prescaling
divider IC18. The output at IC18/4 is passed via the emitter follower 011 and amplifier
stage 012 to IC9b/3, part of the signal selection syttem described in paragraph 4.17.
AGC and Attenuator
4.6 The amplified signals at IClS/l0 are applied via C49 to the AGC detector
D16/C53. Increasing amplitude causes the poteMial at the D16/C53 junction to
go less positive.
4-1
9916 Vol. 2