DATE: 01 March 1993
8645A Synthesized Signal Generator
Serial Numbers: 0000A00000 / 3203A00368
RPP Module Modification Reduces Noise Floor of RF Output
Duplicate Service Notes:
8643A-01A
8644A-04
8644B-01A
70320A-01A
Parts Required:None
Situation:
The RPP (Reverse Power Protection) module protects the RF output circuitry from damage. Instruments with serial numbers noted above have +15 Vdc and -15Vdc bias voltage
connected to the RPP module. It has been noted that the noise floor of the instrument is
higher when the RPP module is connected to these bias voltages. Removing the bias voltages from the RPP module reduces the noise floor and does not affect the instrument’s
ability to protect the RF output circuitry. The typical reduction of the noise floor (for output levels less than -120 dBm) is 3dB.
8645A-02A
SUPERSEDES: 8645A-02
Continued
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© 1993 AGILENT TECHNOLOGIES
PRINTED IN U.S.A.
SERVICE NOTE
ADMINISTRATIVE INFORMATION
AUTHOR: LHL
ENTITY: 1000
MODIFICATION AVAILABLE
SERVICE NOTE CLASSIFICATION:
ACTION
CATEGORY:
LOCATION
CATEGORY:
CUSTOMER INSTALLABLE
ON-SITE
SERVICE CENTER
PERFORMANCE ENHANCEMENT
SERVICE/RELIABILITY ENHANCEMENT
AVAILABLE UNTIL:
ADDITIONAL INFORMATION:
AGREEABLE TIME
Modification purchased by
customer
NOTE: All instruments, with or without the bias voltages applied to the RPP module,
will meet or exceed published phase noise specifications. Other specifications such as
RPP trip level, maximum power, SWR, harmonics and residual FM are not affected by
removing the bias voltage. The main application affected by reducing the noise floor is
when the instrument is used to measure SINAD of an FM reciever.
Solution/Action:
Clip out or de-solder two jumper wires which connect +15 Vdc and -15Vdc to the RPP
Module. Refer to Figure 1 for module/component location. Re-calibration is not
required.
Service Note 8645A-02APage 2
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