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

A6 Output (HP 8648A) The output assembly takes the 500 to 1000 MHz signal from the A5
assembly and the 1 GHz LO signal from the A4 assembly to generate
the output frequency range of 0.1 to 1000 MHz in three bands. The
output assembly also handles the filtering, AM, and amplitude leveling
functions.
The three frequency bands range from 0.1 to 249 MHz, 249 to
501 MHz and 501 to 1000 MHz. The 0.1 to 250 MHz band is
heterodyned from the 1 GHz LO signal and the 500 to 1000 MHz main
band signal. The 250 to 500 MHz signal is derived by dividing the
500 to 1000 MHz main band signal by two.
Filtering is handled by separate low-pass filters for each frequency
band.
AM is done using two separate modulators, one for the divide band
and one dual-output modulator for the main and heterodyne bands.
The AM signal from the A3 modulation section for both modulators is
summed into the ALC loop integrator.
Amplitude leveling is handled with an ALC loop to lock the level
and an amplitude DAC to set the level. The error signal from the
ALC integrator is sent to either of the two modulators along with the
summed AM signal.
The output assembly contains a calibration EEROM that contains
calibration data. This data must be regenerated anytime an A6
assembly is replaced.
A6 output The A6 output module works in conjunction with the A10 frequency
(HP 8648B’C’D)
extension module and differs from HP 8648A operation in the
following ways:
1. AM is input to the output module only for frequencies
5 1000 MHz. For higher frequencies, this signal goes to the A10
frequency extension module.
2. The ALC detector voltage for all frequencies (not just > 1000 MHz)
is now generated on the A10 frequency extension module.
3. The range of the RF input to mixer in the A6 Output has been
changed to allow the mixer to output signals between 9 kHz and
249 MHz to the Al0 frequency extension assembly.
A7 Attenuator The attenuator assembly contains the attenuators, the
reverse-power-protection circuitry and the temperature-sense
(HP 86484 circuitry
The attenuator assembly contains a calibration EEROM that contains
calibration data. This data must be regenerated anytime the A7
assembly is replaced.
Theory of Operation 5a-7