TM 11-6625-2837-14&P-7 TECHNICAL MANUAL OPERATOR'S ...

SERVICE SHEET 7
TM 11-6625-2837-14 & P-7
NOTE
When a malfunction occurs, refer to Section VIII of the Model 8660-series mainframe manual to begin
troubleshooting (Systems Troubleshooting Guide). If the information then indicates possible problems in the RF
Section, refer to the Systems Troubleshooting information Service Sheet 1 in this manual. This information may be
used to isolate the defect to the RF Section, another plug-in, or the mainframe. If the problem is in this plug-in, refer
to Service Sheet 2 for further troubleshooting information .
PRINCIPLES OF OPERATION
General
The detected signal output from the A4 Detector Amplifier Assembly is coupled into the A3 ALC Amplifier Assembly where it is
compared to the reference input. Any difference in dc input levels causes an error output signal (i.e., a change from the loop quiescent
state) at the difference amplifier output A3TP1. The error signal is coupled through the Gain-Shaping Amplifier to the A5 Modulator
Assembly which controls the RF output level. The change in RF output level is reflected in a dc level change at the input to the dc
amplifier. The change serves to balance the original error output signal at A3TP1.
A10 Reference Assembly
The Reference Assembly output is coupled to the ALC circuit where it is compared to the Detector Amplifier output. An error signal is
generated which causes the RF signal to follow the reference dc level or, in AM mode, a low frequency ac signal which is
superimposed on the reference dc output.
A reference dc level is established by A1OVR1. This dc level is coupled to the inverting input of AlOUl where (in the +10 dBm range
only) a small RF Detector diode linearity compensation current is added from the 10H input through resistor AlOR14. The output of
AlOUl passes through a remotely controlled attenuator or an adjustable voltage divider which includes R1 VERNIER Control. This
provides fine adjustment of the reference output, i.e., the RF Output level over a 10 dB range.
The Amplitude Modulation drive signal is input at the non-inverting input of A1OU1. The AM Gain input is a dc compensation signal
which effects the level of the AM drive input. As the VERNIER control is rotated cw, the dc level goes more negative which increases
the RF Output level. At the same time a negative change of the AM Gain compensation increases the modulation drive signal
attenuation of the AM drive signal input to A10U1. The resulting increase in modulation drive signal at the output of AlOUl tends to
keep the percentage modulation level constant with change in RF output level.
In the remote mode, the front panel VERNIER control of the RF output level is inhibited and the 1 dB step attenuator assumes
"vernier" control over
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