Rf Path Block Description (Frequency Generation, Level Control, And Modulation); Frequency Generation; A29 20 Ghz Doubler; A6 Frac-N - Agilent Technologies PSG Series Service Manual

Troubleshooting

RF Path Block Description (Frequency Generation, Level Control, and Modulation)

RF Path Block Description
(Frequency Generation, Level Control, and Modulation)

Frequency Generation

The RF is used to generate, modulate and control the level of the output frequencies. The Synthesis Loop
Block Description describes how the fundamental frequencies of 3.2 GHz to 10 GHz are generated using the
YO, Sampler, and Frac-N. Frequencies below 3.2 GHz are generated by dividing down the fundamental
frequency. Output frequencies between 3.2 and 10 GHz are the RF fundamental frequencies generated by the
YIG Oscillator. Output frequencies of 10 and 20 GHz are generated by doubling the 5 to 10 GHz fundamental
frequency. Output frequencies above 20 GHz are generated by doubling the 10 to 20 GHz frequencies. The RF
Path consists of the A29 20 GHz Doubler, A6 Frac-N, A8 Output, A30 Modulation Filter, and A27 40 GHz
Doubler.

A29 20 GHz Doubler

Besides providing signal to the A5 Sampler as discussed in Synthesis Loop overview, the A29 20 GHz Doubler
is a key par of the RF path. For output frequencies below 3.2 GHz, the A29 20 GHz Doubler provides RF input
to the A6 Frac-N For output frequencies 3.2 to 10 GHz, the A29 20 GHz Doubler passes through the YIG
Oscillator frequencies. For output frequencies of 10 to 20 GHz, the A29 20 GHz Doubler doubles the 5 to
10 GHz fundamental. For frequencies 3.2 GHz and above, the A29 20 GHz Doubler output is routed to the
A30 Modulation Filter.

A6 Frac-N

The A6 Frac-N is part of the Synthesis Loop and the RF path. Frequencies below 3.2 GHz are generated on
the A6 Frac-N by dividing down the fundamental frequency. Frequencies above 3.2 GHz do not go through the
A6 Frac-N. On the A6 Frac-N, the RF signal from the A29 20 GHz Doubler is amplified, filtered, divided, and
then amplified again before being routed to the A8 Output.
A pre-level bias voltage from the A8 Output is fed back to the A6 Frac-N to maintain the desired RF output
level from the A6 Frac-N to the A8 Output. If the A8 Output is removed from the signal generator while the
signal generator is powered on, the correct bias is maintained and the RF power level to the A8 Output can be
checked.

A8 Output

The A8 Output provides pre-level bias voltage to the A6 Frac-N, RF output leveling control, pulse modulation,
and amplitude modulation, and frequency under range circuitry. The ALC diode is used to control the RF
output power for frequencies up to 3.2 GHz. With no bias applied to the ALC diode output power goes to the
minimum level the circuit can provide. In closed loop operation, the A10 ALC uses a negative voltage from the
detectors to maintain the bias on the ALC diode. Pulse modulation (RF pulsed on) is achieved by applying a
+5 Vdc to the pulse circuitry on the A8 Output. Under range frequencies below 250 MHz are generated on the
A8 Output by mixing the RF signal with a 1 GHz signal from the A7 Reference. The A8 Output signals pass
through the A23 Low Band Coupler/Detector before going to the A30 Modulation Filter.
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