Installation guide

Troubleshooting
Block Descriptions for Option 501, 502, 503, 504
1-119
made between a reference voltage and the detected voltage. If the detected and reference voltage levels agree,
the modulator drive current remains constant. If the detected and reference voltage levels do not agree, the
modulator drive current changes causing the RF output power to increase or decrease until the reference and
detected voltages agree. In open loop operation or ALC OFF mode, only the reference voltage is used to
control the modulation drive current. The reference voltage is determined by the desired power setting and
includes the stored calibration data used to compensate for any losses that occur after the detector. The
reference voltage is generated on the A13 Output by a DAC and is controlled by the A12 CPU.
Analog Modulation
An Internal Modulation Source Function Generator, located on the A23 Motherboard, is used to provide
AM, FM, PM, and Pulse modulation capabilities. To improve phase modulation control, this function
generator is tied to the 10 MHz reference signal from the A18 Reference. The function generator’s signal is
routed to the A18 Reference, which contains a multiplexer. The multiplexer is controlled through the front
panel and may be used to select the modulation source. External modulation may be applied through the
EXT 1 and EXT 2 front panel inputs. There is also a feature that allows internally generated signals to be
routed to the LF Output on the front panel. AM and Pulse modulation signals are routed to the A13 Output
while FM and PM modulations are routed to the A17 Synthesizer (Option 501, 502, 503, 504).
Digital Modulation
The A10 I/Q Multiplexer routes the front panel I/Q baseband signals to the A13 Output so that they can be
used to modulate the RF signal. The A10 I/Q Multiplexer also routes the front panel I/Q signals to the rear
panel. Along with the original I/Q signal, an inverted I/Q signal is available at the rear panel.
If the signal generator contains an A7 Baseband Generator (Option 001 or Option 002), it may provide the
baseband I/Q signals; it also has the capability of burst modulation. The A10 I/Q Multiplexer may select
which baseband signal to use and route the signal in the same manner as the external front panel I/Q signals.
The I/Q signals are simultaneously routed by the A10 I/Q Multiplexer to the A18 Reference so they may be
used to modulate AM, FM, and PM.