HP 8648 A/B/C/D - Changpuak.ch

A10 Frequency
Extension
(HP 8648BKYD)
A 11 Attenuator
(HP 8648B/C/D)
Al2 Reverse Power
Protection
(HP 8648BKYD)
5a-8 Theory of Operation
The main input to the A10 frequency extension module is the 9 kHz
to 1000 MHz RF from the A6 output module. It operates in three
frequency bands to cover the extended frequency range of the
HP 8648B/C/D:
9 kHz to 1000 MHz
> 1000 MHz to 2000 MHz
> 2000 MHz to 4000 MHz
For frequencies 5 1000 MHz, the module operates as an amplifier
and provides a dc voltage to the A6 output module that is used for
ALC. This dc voltage represents the detected RF output level from
the module and is used as an input to the ALC integrator on the A6
module.
For RF output frequencies between 1000 and 2000 MHz, a doubler
is used on the 500 to 1000 MHz input signal. Three bandpass filters
are used over this frequency range to control harmonics. A pre-level
detector provides a dc voltage to the A6 output module that is used to
drive the ALC loop integrator on the A6 output module. An additional
ALC loop is provided on this module for frequencies > 1000 MHz.
For RF output frequencies between 2000 and 4000 MHz an additional
doubler is used. For this frequency range, the signal from the A6
output module is between 500 and 1000 MHz. ALC operation is the
same as for the 1000 to 2000 MHz band.
The A10 assembly contains a calibration EEROM that contains
calibration data. This data must be regenerated anytime the A10
assembly is replaced.
The attenuator is a 4-section attenuator (10, 20, 30, and 60 dB
sections) that provides 130 dB attenuation in 10 dB steps.
Calibration EEROM on the motherboard contains calibration data
specific to this assembly. It needs to be updated whenever the
attenuator is replaced.
The reverse power protection assembly is designed to protect the
instrument from power applied to the RF output from an external
source. It opens the RF path when an excessive power level is
detected. When it is tripped the front panel indicates that RF power
is off. To reset the RPP assembly, just turn the RF power on again.
Calibration EEROM on the motherboard contains calibration data
specific to this assembly. It needs to be updated whenever the RPP
assembly is replaced.