HP 8340B Manual page 183

A54 YO Pretune/Delay Compensation Assembly Theory of Operation
The A54 YO pretune/delay compensation
assembly performs three major functions:
•
It
provides
a
DC voltage (PRETUNE) to
the ASS YO driver that
is
proportional to the frequency to
which the
YO
is
being phase-locked. The YO sensitivity of this line
is
—2.5
V/GHz
(of YO
fre¬
quency).
PRETUNE
is
also used by the A28 SYTM driver to tune the A13 switched YIG-tuned
multiplier (located in
the RF
section).
•
It
generates
the kick pulses that are necessary at
a
YO
retrace to eliminate magnetic hysteresis.
These pulses are of constant amplitude, corresponding to about 2.5 GHz, and are of varying
width. The width is
a
function
of the
YO
start frequency and sweep
width of the previous sweep as
well as the
YO
start frequency of the next sweep. These pulses are subtracted from the phase-
lock
PRETUNE
voltage and temporarily tune the
YO 2.5 GHz below
the
next phase-lock
fre¬
quency.
•
It
provides a
voltage (VCOMP) to the ASS YO driver that compensates for
the
YO's
normal delay at
start of sweep.
ASS YO Driver Assembly Theory of Operation
The ASS
YO driver performs the following
functions:
•
It
acts as a
voltage-to-current converter to change the
PRETUNE voltage (sensitivity
=
—2.S
V/
GHz)
to
YO
main coil
current
(sensitivity
is
approximately 24 ma/GHz). The two
sensitivities
mentioned above are expressed
in
terms
of
YO frequency,
not
RF output frequency.
•
It
provides the summing point for the low frequency portion
(<100
Hz) of
the
YO phase-locked
loop error voltage (YO TUNE).
•
It
provides the summing point for the
YO delay
compensation voltage
(VCOMP).
•
It provides the summing point for the YO
coil
offset current.
•
It provides the driver
circuitry for the YO retrace
kick pulse.
HP 8340B/41B
Sweep Generator
-
YO
Loop Theory
of Operation D-13