1 INTRODUCTION AND SPECIFICATION
GENERAL
This handbook
describes:-
(1) the standard R499A receiver and the remote
control system (comprising motor switching unit
and RC116A control unit)
(2) the ISB version
of
the receiver (designated
R499/ISB) and remote control system (comprising
motor
switching unit and RC116/ISB control unit)
The ISB version
of
the receiver is intended for use
with the ARUIOA ISB Adaptor which
is
described in a
separate handbook entitled ISB
ADAPTOR
Type
ARUIOA.
The R499A
is
a solid state receiver designed for a
variety
of
applications in point-to-point communications.
It
is
especially adaptable to the requirements
of
individual
systems. The receiver employs single frequency conversion
and a nominal
IF
of
1.4
MHz,
with
an
AM detector and
a separate product detector for reception
of
SSB
signals.
The basic version
is
for
SSB
service,
but
by appropriate
specification
of
optional filters and BFO as internal
sub-units, full
CW
and DSB modes
of
reception are
possible. When used in conjunction with the type
ARUIOA ISB Adaptor unit, the receiver can
be
used for
the reception
of
ISB transmissions.
FREQUENCY COVERAGE
The basic frequency coverage
is
1.5
MHzto
30
MHz,
but filters can be fitted to give additional coverage
of
the
255
kHz to
525
kHz
band. Pre-aligned
HF
filter sets are
available for fitting after the receiver has been installed,
if
desired.
RECEPTION
MODES
Crystal filters are fitted according to the services
required, and are available for CW, SSB, DSB and ISB
modes
of
operation. The CW filter
is
optional for all
versions
of
the R499, as
is
also the BFO module.
The
CW filter and two other filters can be fitted.
By
suitable choice
of
local oscillator crystals, to
translate the wanted signal to
an
IF
signal within the
3 kHz passband
of
the
SSB
filter, and by selecting the
frequency
of
the re-insertion oscillator (two frequencies
are available, selected as required by the Channel switch),
the
SSB
filter may be used for the reception
of
the modes
of
transmission detailed in the specification.
For
optimum reception
of
AI however, use
of
the
CW filter with a 200 Hz bandwidth,
is
recommended.
For
A3, optimum performance
is
achieved by use
of
the
DSB filter which has a
~
kHz bandwidth.
AGC
Comprehensive distributed
AGC
is
employed with
different decay and attack times for various modes
of
operation. The full decay time
is
dependent
upon
accumulation
of
signal for
200
msec
or
more, which pre-
vents short bursts
of
noise from paralysing the receiver.
887-l
The decay time is automatically selected by a front-panel
Service switch,
but
an
additional switch enables the decay
time-constant to be divided by three, and
is
of
use during
rapid fading. The
AGC
can be switched off when
not
required.
Two
AGC
systems are incorporated. One
is
operated
by the output from the
RF
amplifier and controls an
attenuator
at
the front end. The other is fed from
the
last
IF
stage and
is
applied in sequence over three
IF
stages, as well as supplementing the front-end
AGC
action. Thus the aerial circuit is capable
of
withstanding
an
input
of
30V e.m.f. from a
50
ohm
source.
IF
AND AF GAIN
In
addition to selecting the bandwidth and
AGC
constants appropriate to the required service, the Service
switch also adjusts
IF
and
AF
gain so
that:
(1) All services give virtually the same
AF
output
level
(provided only
that
the signal is above
AGC
threshold).
(2) Any signal which
is
large enough to provide approxi-
mately
14
dB signal-to-noise ratio also provides full
AF
output
e.g. for a given signal-to-noise ratio, a
much
smaller signal
is
required in
CW
mode
than
in, for
example,
AM
mode; this
is
because
of
the narrower
bandwidth
of
CW
filters. Thus, the
IF
gain
is
increased
for
CW
reception so
that
a small
CW
signal can be heard.
SQUELCH
A squelch system
is
incorporated. To guard against
incorrect setting
of
the squelch control and consequent
loss
of
wanted signals, the squelch does not completely
cut off all output,
but
reduces it by approximately 30 dB
so as to keep the audio noise
output
below annoyance
level. This serves as an indication
that
the receiver is still
operative and allows wanted signals to be heard even
if
the squelch has been set
at
too
high a level.
OPTIMUM
CONTROL
SETTINGS
To assist operators unfamiliar with the receiver,
typical
or
normal settings
of
controls are indicated by
red spots. Once the controls are set to the indicated
positions, relatively
few
adjustments to the controls need
be
made.
As
a built-in check, the Service switch
has
a
TEST setting
at
which an
output
from the carrier rein-
sertion oscillator
is
injected into the first
IF
stage. Correct
operation
of
the IF stages
at
this setting
is
indicated
by
a
'test' reading
on
the front panel S-meter.
ADDITIONAL FACILITIES
For
ISB reception, the ARUIOA Adaptor
is
em-
ployed. One sideband filter
is
fitted in the R499A and the
other in the ARUlOA. Sideband filters for this purpose
are available with bandwidths
of
2.75kHz
or
5.75 kHz.
The R499A and the ARUlOA have separate
AGC
sys-
tems and line outputs with associated level adjustments.
In
addition, each unit has its own meter for monitoring
of
incoming signals and line levels. The internal loud-
speaker in the R499A can be switched to monitor the
output
from either unit. ·
1-1
