A203
BAND
3
h4lCROWAVE CONVERTER
The A203 Microwave Converter consists of three sub-assemblies.
A201A Voltage Control Oscillator
A201B IF Amplifier
A202 Microwave big)
CAUTION
Disassembly of the A202 Microwave assembly, or
removal of
it
from the A201A VCO or A201 B IF
.-.
Amplifier will void the EIP warranty.
The assembly drawing and schematic for both the VCO and IF circuits are included only for reference. The
entire A203 assembly must be tested
as
a
complete unit to ensure proper performance of the counter.
Repair of the A202 Microwave assembly can only be done
at
the factory. The VCO and IF Amplifier
boards require special test equipment, therefore field repair
is
not recommended.
The Band
3 Converter
is
a
complete microwave subsystem (see Figure 2031) which converts an input signal
in the 1 to 18 (26.5)
GHz range down to an IF of 125MHz. Down conversion
is
achieved in this heterodyne
system by combining the input signal with
a
harmonic of
a
precisely known reference signal (Fvco). The
mixer then produces
a
signal (FIF) equal to the difference between the input and reference harmonic. If
this difference
is
close to 125MHz.
it
is
amplified to
a
level of about OdBm and then counted. The input
signal
is
then determined from the equation FIN
=
NFVCO
+
FIF. FVCO
is
set by the instrument pro-
gram via
a
phase locked loop located on the converter control board (A108) and
is
thus known exactly.
Harmonics of the VCO are produced by the comb generator and coupled to the mixer. The frequency
ranges of the VCO and IF are such that for any VCO frequency and any input frequency, only one harm-
onic can produce an IF frequency. The YIG filter located between the RF input
and.the mixer
is
used to
approximatley determine the input frequency and from this information the desired values of N,
FVCO
and
+/-
are determined.
Two other outputs are obtained from the Band 3 Converter. The first
is
an analog signal which
is
a
measure
of input RF power. The second
is
a
digital signal (IF THRESHOLD) which indicates that an IF signal
exists
at
a
level of -3dBm or greater.
).
Scans by ArtekMedia © 2007
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