Installation guide

Troubleshooting
Block Descriptions for Option 501, 502, 503, 504
1-127
A18 Reference (Option 501, 502, 503, 504)
or A18 Reference (Option 501, 502, 503, 504 with Option 1E5)
or A18 Reference (Option UNJ or Option 506) The A18 Reference is the heart of the Analog Modulation
Block and is responsible for routing all analog modulation drive input signals to the appropriate drive
circuits. The Internal Modulation Source Function Generator (located on the A23 Motherboard), EXT 1 and
EXT 2 (located on the front panel), as well as Audio 1 and Audio 2 (located on the A10 I/Q Multiplexer) input
signals can all be individually switched to AM, FM, and Pulse modulation drive circuits.
The modulation drive outputs are:
• Frequency Modulation (FM)
— On Option 501, 502, 503, 504 signal generators, this drive signal goes to the
A17 Synthesizer (Option 501, 502, 503, 504) and is used to modulate the VCO.
— On Option UNJ and Option 506 signal generators, this drive signal goes to the
A16 Frac-N (Option UNJ or Option 506) and is used to modulate the Frac-N VCO.
It is also routed to the YO DRIVER and used to modulate the FM coil of the YIG; the YIG is located on
the A21 YTO Driver (Option UNJ or Option 506).
• Phase Modulation(PM)
PM uses the same signal flow as FM, but is filtered differently.
•PULSE Modulation
This drive signal is directed to the A13 Output and is used to drive the Scan/Burst modulator, which in
turn, pulse-modulates the main RF signal.
• Amplitude Modulation (AM)
This drive signal is directed to the A13 Output and is used to drive the Scan/Burst modulator and the
ALC modulators, which in turn, amplitude modulate the main RF signal.
• LFO out drive signal
This drive signal is directed to the front panel and is used to modulate external equipment.