An
extended hysteresis facility allows for
extended electronic control of RF output level
without
introducing mechanical attenuator
transients when testing squelch systems.
A low intermodulation
mode can be selected which disables the RF levelling
system and
improves
the
intermodulation
performance when
combining
the
outputs of
two
signal generators.
A choice of calibration units
is
available
to the operator and provision is made
for the
simple conversion of units
(for example, dBm to jiV). Calibration
data
for
the output level is
held
in
memory
and may be altered from
the front panel or over the interface bus.
The output level
can be offset by up to ±2 dB by keyboard entry. Offsets
from the
calibrated value
may be used to compensate for
cable or switching losses external
to
the
generator. This facility can
be used as a means of deliberately offsetting
the output level to
ensure that
all generators in an area give identical
measurements. While using the offsetting
facility,
the principal calibration of the generator
is not lost and may be returned
to at any time.
An electronic
trip protects the generator output against reverse
power of up to 50 W,
preventing
damage to output circuits when RF or DC
power is accidently applied.
Modulation
Comprehensive
amplitude, frequency (plus wide bandwidth
FM), phase and optional
pulse
modulation are provided for testing a wide
range of receivers. An internal modulation
oscillator is provided, having
a
frequency
range of 0. 1 Hz to 500 kHz, with
a resolution of
0.1 Hz. A
second modulation
oscillator
can be included
as an option. Two independent BNC
inputs on the front panel allow external
modulation signals to be mixed with
the
internal
signal(s). Therefore,
a maximum of four modulation sources may
be
available
at one time. These
sources
may be combined to give the
single, dual, composite and dual composite modes,
see
'MODULATION MODES’,
Chap.
3-1
.
The signalling facility allows testing
of radio equipment with sequential and sub-audible
tone capability.
The
sequential
calling tone system
is
accessible
from
the
utility menu for all four
modulation
modes. Sub-audible calling
tones are specified
within
the modulation source select
display.
Incrementing
All major parameters can
be incremented or decremented in step
sizes entered
via
keyboard entry
or the GPIB. If no step size
is entered for a parameter, the steps are preset to
1 kHz for earner frequency,
1 kHz for modulation oscillator and LF frequency, 1
kHz for FM
deviation,
1
%
for
AM depth and 1 dB for output level.
In addition the rotary
control can be used to vary the parameter with the sensitivity
of the
knob being changed
by means of the
xlO
and
-*-10
keys.
Sweep
The sweep
capability of the 2040 series allows comprehensive
testing of systems. Four
parameters
are used to specify sweep; start, stop,
number of steps and time per step. These
are
specified by the user, with
upper and
lower
limits for the parameter values
being dependent on
the function.
The sweep markers menu is available
by soft key selection on the sweep display,
allowing the placement of up
to
five user
defined markers.
Non-volatile
memory
The non-volatile memory allows
50 complete instrument settings,
50
partial
settings, 100
carrier frequency
settings, 20 sweep settings and 20 signalling
tone sequences to be stored for
later
use at any time.
46882-074C
1-3
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