HP 8340A Service Manual page 169

SMALL DELTA F SWITCH
US functions as a single-pole double-throw switch,
3 to 6 MHz from U2 or 0.15 to 0.30 MHz from Ul,
Up Converter. The required range is selected by a TTL signal
from the A42 PLL2 Divider)
levels to ECL levels.
For 20-30 loop sweeps between 5 kHz and 100 kHz,
HIGH and the 3 to 6 MHz divider output is routed to the A39 PLL3
Up Converter. For sweeps less than 5 kHz,
selecting the 0.15 to 0.30 MHz output.
0.1-5 MHz DELTA
For delta F or sweep widths of 0.1 to 5 MHz,
output is used. The output of U3 in Frequency Dividers
is routed through U6D,
switch with 90 dB of isolation in the off state. The TTL signal
(SWl from the A42 PLL2 Divider)
For maximum isolation,
separate packages. Any stray signals that do reach the output
will be a common-mode input to transformer Tl. Since Tl will only
respond to differential mode signals from U7D,
signals will be rejected.
C25 and Ll4 filter the output to reduce spurious responses.
Model 8340A - Service
E
on Pl-22. R33 and R34 shift the TTL
F SWITCH F
U7D, and Tl. This combination serves as a
the two gates
Scans by HB9HCA and HB9FSX
SW2 is a TTL LOW,
the 15 to 30 MHz
on Pl-24 controls this switch.
(U6D, U7D)
these common-mode
routing either
to the A39 PLL3
(SW2
SW2 is a TTL
(Block D)
are contained in
8-231/8-232