GENERAL INFORMATION
A choice of calibration units is available to the operator and provision is made for the
simple conversion of units (for example, dBm to
μ
V). 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 accidentally applied.
Modulation
Comprehensive amplitude, frequency (plus wide bandwidth FM), phase and optional
pulse modulation are provided for testing a wide range of receivers. The instrument also
provides internally generated modulation wave forms or the testing of Instrument Landing
Systems (ILS) and VHF Omni-Range (VOR) beacons. Two internal modulation oscillators are
provided, each having a frequency range of 0.1 Hz to 500 kHz, with a resolution of 0.1 Hz. Two
independent BNC inputs on the front panel allow external modulation signals to be mixed with
the internal signal(s). Therefore, a maximum of five modulation sources may be available at one
time. These sources may be combined to give the single, dual, composite, dual composite and
avionics modes.
The signaling 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 five
modulation modes. Sub-audible calling tones are specified within the modulation source select
display.
Avionics modes
The avionics capability provides internal generation of waveforms suitable for testing
Instrument Landing Systems (ILS) and VHF Omnidirectional Radio Range (VOR) systems.
ILS mode
In ILS mode the SDM (Sum of Depth of Modulation) of the 90 Hz and 150 Hz tones is
entered to a resolution of 0.1% AM depth. The DDM (Difference in Depth of Modulation) is
entered to a resolution of 0.01% depth for a DDM up to 20% and 0.1% for higher DDM settings.
A choice of which tone is dominant is available to the user. DDM is also displayed in
μ
A, to a
resolution of 0.01
μ
A.
The 30 Hz repetition frequency of the ILS waveform can be adjusted in 0.1 Hz steps. For
0% DDM additional modulation signals can be added to the ILS waveform.
Marker beacon mode
In marker beacon mode the outer, middle and inner beacons can be tested by simple key
selection.
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