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Tables 1 through 8 provide information that is useful in troubleshooting the A4A9 IF Control
Assembly.
Table 1 (0.0 to -1.9 dB Control Truth Table) and Table 2 (0 to -9 dB Control Truth Table)
illustrate the A4A9 IF Control control line switching for the A4A5 Step Gain variable and
fixed attenuators. These tables must be used in conjunction with one another. Table 1 is the
truth table for the variable attenuator control lines (A.1 dB, A.2 dB, A.4 dB, A.8 dB, and Al
for the fixed attenuator control lines (A2 dB, A4 dB, and A8 dB) of the Input Latches (A)
function block on the A4A9 assembly. Together these two tables can be used to determine the
states for each of these control lines for reference levels in 0.1 dB steps. As the reference level
changes, 0.1 dB to 9.9 dB of attenuation is added or removed from the IF signal path.
When using Table 1 (0.0 to -1.9 dB Control Truth Table) and Table 2 (0 to
Note
-9 dB Control Truth Table) for troubleshooting, the reference level must be
I
input using the front-panel keyboard. The truth tables (Tables 1 and 2) are
not valid when the spectrum analyzer is using correction factors (KSX) or
when the RPG knob is used to change the reference level. The fixed and
variable attenuators are set differently than the truth tables show in these
modes.
Table 1 shows the variable attenuator control line states for each .l dB step of reference level
between 0 dBm and -1.9 dBm. This table repeats for every 2 dB change of the spectrum
analyzer's reference level. For example, in addition to this being the truth table for reference
levels between 0.0 and -1.9 dBm, it is also the truth table for reference levels between -2.0
and -3.9 dBm, between -4.0 and -5.9 dBm, between -6.0 and -7.9 dBm, between -8.0 and
-9.9 dBm, and so forth.
Table 2 shows the fixed attenuator control line states of reference levels between 0 dBm and
-9 dBm. The fixed attenuators change the reference level in 2 dB steps. This table repeats
itself with every 10 dB change of the spectrum analyzer's reference level. For example, in
addition to this being the truth table for reference levels between 0 and -9 dBm, it is also
the truth table for reference levels between -10 and -19 dBm, between -20 and -29 dBm,
between -30 and -39 dBm, and so forth.
To determine the levels for all control lines at the outputs of the input latches, both Table 1
and Table 2 must be used. For example, if the reference level of the spectrum analyzer is 0.0
and Al dB are high. Table 2 shows that the state of control line A8 dB is high. Thus when
the spectrum analyzer has a reference level of 0.0 dBm, control lines A.1 dB, A.8 dB, Al dB,
and A8 dB are high at the output of the input latches (Function Block A).
As another example, if the spectrum analyzer has a reference level of -33.4 dBm, use the
-2 (-3) dBm row of Table 2 because it is representative for reference levels from -30 dB
through -39 dBm. Use the -1.4 dBm column of Table 1 because Table 1 is representative for
reference levels between -32 dBm and -33.9 dBm. Using Tables 1 and 2, a reference level
of 33.4 dBm has control lines A.1 dB, A.4 dB, A2 dB, and A4 dB high at the output of the
input latches.
4 A4A9
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