A14 High Band Power Amplifier; A16 High Band Modulator/Splitter; A17 Low Band Mixer - HP 8340B Manual

The YIG tuned
filter is
a
tunable bandpass
filter.
It is
tuned to the RF output frequency by the SYTM
coil
drive-current (supplied
by the
A28 SYTM
driver).
The filter
bandpass frequency
is determined
by
a
small
YIG sphere whose resonant
frequency depends on the strength of the surrounding magnetic
field.
The magnetic
field is
established by
an
opposing pair of electromagnet
coils.
Changing the
current through the coils changes the magnetic
field
strength, and, consequently, the bandpass
fre¬
quency. Typically, the bandcross
is
±12
MHz.
A14 HIGH BAND POWER AMPLIFIER
The
A14 high band power amplifier
is
a
GaAs
FET (gallium arsenide field
effect transistor) that covers
the
2.3
to
7.0 GHz
frequency range. The amplifier provides approximately 26 dBm output power. The
small-signal gain
is
typically 25 dB, but at
maximum leveled output, the
amplifier can be 10 dB
into
compression.
A
7.0
GHz notch filter reduces harmonics out of
the
amplifier. This filter is
switched
in
when
the
amplifier operates below 4.5
GHz.
A15 LOW BAND LOW PASS FILTER
The A15
low
pass
filter attenuates harmonics from the 3.7 GHz
oscillator to minimize unwanted
mixing
products produced
in the A17 low band mixer.
A16 HIGH BAND MODULATOR/SPLITTER
The
A16 modulator/splitter divides the YIG
oscillator output into three
paths:
•
The low band output provides LO drive for the low band mixer.
•
The
high
band output feeds the
high band amplifier.
•
The third output feeds the AUX
OUTPUT
via
an internal coupler.
A17 LOW BAND MIXER
The A17 mixer mixes
a
fixed 3.7 GHz signal with the swept 3.71 to
6.0 GHz YO output, producing the
0.01
to 2.3
GHz RF
output of low band.
A
3.7 GHz directional filter (before the single balanced mixer) and
a
2.75 GHz
low pass
filter (at the
output) minimize
unwanted mixing products. The swept YO
output,
after passing through the A16
modulator/splitter, acts as the local oscillator signal for
the mixer. Conversion loss is
approximately
9
dB at 1
GHz
HP 8340B/41B
RF
Section Theory of Operation H-5