HP 8340A Service Manual page 205

SWEEP GENERATOR DESCRIPTION
Introduction
The assemblies documented in this functional group that cause the
frequency of the 8340A to sweep are A58 sweep Generator,
Pretune/Delay Compensation board,
When the YO loop phase-locks at the start frequency of an
instrument sweep or at the start of a new band,
Pretune/Delay Compensation board provides PRETUNE voltage to the
A55 YO Driver. PRETUNE is a de voltage proportional to
frequency at which the YO is locking. The sensitivity of this
voltage is -2.5 volts/GHz. The A55 YO Driver converts this
voltage to a current
frequency. This current is fed to the YO Main Coil where it tunes
the frequency of the YO to be within the phase-lock range of the·
YO loop.
For sweep widths
YO phase-locked loop by activating the sample and hold, thus
holding YO TUNE con�tant at its phase-locked value. The A58 Sweep
Generator then provides a voltage ramp which is summed with the
PRETUNE voltage on the A54 YO Pretune/Delay Compensation board.
The resulting voltage ramp produces a current ramp from the A55
YO Driver board which in turn sweeps the frequency of the YO.
VSWP is also used on the A54 YO Pretune/Delay Compensation board
to produce another negative going ramp called VCOMP. This is
added to PRETUNE
eddy-current induced swept frequency error inherent in the YO
magnetic structure.
When a bandcrossing or end of sweep is reached,
Bandcross) and HSP
Marker/Bandcross board. This causes VSWP to pause
Then the instrument processor pulls LRSP
which resets VSWP to zero volts
. To erase the magnetic memory of the YO magnetic structure,
instrument processor initiates a retrace kick via the YO RETRACE
KICK PULSE Generator
Compensation board. This pulse is summed with the PRETUNE
voltage. The effect is to temporarily offset the YO frequency by
approximately -2.5 GHz. This intializes the domains in the YO
magnets.
Finally, the instrument processor sets PRETUNE to a value
proportional to the next lock frequency. When the loop is locked,
the sweep sequence is repeated.
Model 8340A - Service
which is also proportional to the lock
>5 MHz, the A49 YO Loop Phase Detector opens the
on the A55 YO Driver board to compensate for the
(High SweeP) are pulled LOW by the A57
•
(Block G) in the A54 YO Pretune/Delay
Scans by HB9HCA and HB9FSX
and A55 YO Driver.
the A54 YO
LBX
(Low Reset sweeP) LOW
A54 YO
the
(Low
(stop ramping).
the