J5/J20 Rf; At3 Isolator - HP 8340B Manual

A18 LOW BAND POWER AMPLIFIER
The A18 low
band
power
amplifier is
a
bipolar amplifier that provides approximately
40 dB of
gain and
20 dBm of output power from 0.01 to
2.3 GHz.
At 20 dBm, harmonic output
is less than —25dBc.
The
A18A1 low band power amplifier bias assembly provides the
bias currents, the +20V,
and the
—10V required by the A18 amplifier. The
amplifier and bias board are matched and attached at the
factory; there are no adjustments or replaceable parts, and the two must be replaced together.
When
you turn the RF
off, or
operate the synthesizer in
high band, the —10V bias
is
removed,
shutting
off
the amplifier.
A63 RF ATTENUATOR
The RF attenuator provides 90 dB of
attenuation,
in
10 dB steps.
Combined with the
range of the ALC
loop, this gives the instrument
a
maximum setable power range of
+20
to —110 dBm. The step
attenuator functions
like four fixed attenuators (one
10,
one 20
and two
30
dB). Latching relays close
contacts that either insert
these attenuators
in
the
RF path or bypass them.
The attenuator
control and drive
circuitry
is located
on
the A24 attenuator driver/SRD bias board.
Insertion loss, with 0
dB
of attenuation selected,
is
less
than 2.8 dB
at 26.5 GHz.
J5/J20 RF OUTPUT CONNECTOR
The J5 (front panel)/J20 (rear panel) RF
output connector
is
not the same on both the HP
8340B
and
the 8341
B.
The
HP 8340B
has
a
male, precision 3.5 mm connector; the HP 8341 B
has
a
female
type-n
connector. Either type has an internal 1000 pF (non-replaceable) DC-blocking capacitor. The
blocking
capacitor can handle up to 50 Vdc.
ATI PERIPHERAL MODE ISOLATOR
The
AT1 isolator provides 20 dB of
isolation, and has less than
1 dB of insertion loss. AT1
improves the
match between the high band
power
amplifier and the switched
YTM.
AT3 ISOLATOR
The AT3
isolator improves the match between the
A15
low band low pass
filter and the A17 low band
mixer
with
20 dB
of
isolation. Coupled
RF
from the high band modulator splitter
is isolated from the
low pass filter, reducing any mismatch signal
propagated
as video feedthrough.
H-6
RF
Section Theory of Operation
HP 8340B/41B