Installation guide

Troubleshooting
Block Descriptions for Option UNJ and Option 506
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Frequency Control
Frequency accuracy and stability are established with the A18 Reference (Option UNJ or Option 506),
A15 Sampler (Option UNJ or Option 506), A16 Frac-N (Option UNJ or Option 506), and the A12 CPU.
Frequency Generation
The YIG oscillator, on the A21 YTO Driver (Option UNJ or Option 506), generates frequencies from
4 GHz to 8 GHz. For frequencies from 250 MHz to 4 GHz, the YIG oscillator is tuned in the 4 to 8 GHz range
and the output is divided by 2, 4, 8, or 16. If the desired frequency is below 250 MHz, an additional mixer is
used. For frequencies > 4 GHz and ≤ 6 GHz (Option 506) the YIG frequency is not divided.
To change frequencies, the A12 CPU controls the A21 YTO Driver and coarse tunes the YIG with a voltage
provided by the pre-tune DAC. The A15 Sampler compares the signal from the YIG to a reference signal and
generates an error voltage proportional to the frequency error. This voltage is summed with the pre-tune DAC
voltage and corrects (fine tunes) the YIG’s output frequency.
The reference signal is provided by the VCO on the A16 Frac-N that is phase-locked to a 10 MHz reference on
the A18 Reference. The A15 Sampler down converts the YIG frequencies to make the comparison with the
reference. The comparison is done by a phase detector, which generates an output voltage proportional to the
difference in frequency/phase. This voltage tunes the YIG until there is no difference in frequency/phase.
Output Power Leveling/Automatic Leveling Control
Output power control circuitry consists of a detector, integrators, two ALC modulators, and other associated
circuitry. This circuitry is commonly referred to as the Automatic Leveling Control (ALC) loop. A small
portion of the RF signal is detected and converted to a dc voltage. In closed loop operation, a comparison is
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 and A14 Extended Frequency Output (Option 506) 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
and A14 Extended Frequency Output (Option 506) while FM and PM modulations are routed to the
A16 Frac-N (Option UNJ or Option 506).
Digital Modulation
The A10 I/Q Multiplexer routes the front panel I/Q baseband signals to the A13 Output and A14 Extended
Frequency Output (Option 506) 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