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I
36) As shown in Fig.
4-3, pressing the S/N key causes the output of the
oscillator to be stored as the S component.
(In this case,
10-dB
signal is applied to the measurement circuit because the output
amplitude of 4.0 dB is displayed,
and the output is not terminated
with a 600-ohm load.)
The INPUT LEVEL meter
(T)
goes into the 10-dB
range and indicates 10 dB
<3.2 V).
The S/N meter @ is placed in
the 0-dB range.
The operation described above is performed for 1.5
seconds as shown in Fig.
4-3.
The S component is then eliminated
and only the N component is left.
(The S component input level of
10 dB is stored and the INPUT LEVEL meter
(7)
retains the deflec¬
tion.)
Because the oscillator provides no output, most of the N
component is the residual noise within the measurement circuit.
The
S/N ratio is calculated from the stored S level and the residual N
level; the range of the meter
(5)
automatically changes, and the
meter provides direct indication of the S/N ratio.
37) The REF ADJ knob
(lO)
has no effect while the S/N ratio is measured.
38) The LPF's and HPF are used for limiting the bandwidth in which the
N component is detected.
Turning on the 30 kHz or 80 kHz LPF key
decreases the deflection of the S/N meter because the S/N ratio is
increased.
The residual noise can be checked by observing the
monitor output with an oscilloscope.
39) The meter range can be switched manually by pressing the RANGING
key
(G)
with the LED in the key on indicating MANUAL mode.
In
this mode,
after the S/N key is pressed and the S component stored,
the 0-dB meter range display LED is lit if the input meter range is
appropriate for the input S component level.
To read the S/N
ratio,
lower the range to the desired level by pressing the T
key of the MEASUREMENT RANGE select keys (G) ■
If an incorrect
input meter range is selected, either LED-built in the INPUT RANGE
OVER/UNDER keys
(G)
annunciates,
indicating excessive input
(OVER)
or too little input
(UNDER)
for 1.5 seconds of S component
measurement period.
Select another range by pressing the key until
the annunciator goes off
during S component measurement.
-When the
key is pressed,
S/N will be measured^without the need of pressing
the S/N key again.
...
After S component has been removed in S/N measurement, the UNDER
.j
Xight will be on.
Note that this is not a warning but a normal
o
N
state measuring N component.
i
X)
M
4-17
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