HP 8340A Service Manual page 209

YO FM Coil Drive
The FM Coil Driver
so that only the high frequency
applied to the YO FM Coil. The resulting output is the YO FM COIL
DRIVE current. The low frequency portion
summed with PRETUNE and applied to the YO Main Coil.
YO Main Coil Drive
The YO MAIN COIL DRIVE current is derived at the A55 YO Driver
from the PRETUNE and YO TUNE voltages. YO TUNE is summed
Block E) with the OFFSET voltage, and PRETUNE is scaled
Block A) by the GAIN adjustment. The YO MAIN COIL DRIVE current
is constructed- as a linear function of the desired YO frequency.
The OFFSET adjustment varies the offset of the curve; the GAIN
adjustment varies the slope. These two adjustments are used to
ensure the tuning accuracy of the YO versus PRETUNE voltage over
its full range of operating frequency. OFFSET has greater effect
on the low end of the range
effect on the high end
The Voltage-to-Current Converter
Driver and the A47 Sense Resistor Assembly are part of the same
circuit. (A47R6 and A47Ql are located externally to be properly
heat sunk.) This circuit converts the
and YO TUNE voltages to the YO MAIN COIL DRIVE current that
drives the YO Main Coil. This completes the YO loop which tunes
and phase-locks the YO.
8-286
Model 8340A - Service
(A49, Block I) has a 100 Hz high pass filter,
(>100 Hz) portion of YO TUNE is
(2.30 GHz), and GAIN has greater
(6.99 GHz).
(A55, Block B) on the A55 YO
Scans by HB9HCA and HB9FSX
(<100 Hz) of YO TUNE is
(scaled) sum of the PRETUNE
(A55,
(A55,