(1)
Voltage Scales
See F i g u r e s
There are t w o black voltage scales : a scale ©
graduated 0 to 10 and a scale © 0 to 3. When the
R A N G E selector @ is a t "1 V \ f o r example, the
division 10 on the scale ® indicates 1 V . A t the " 0 . 3 V "
position, the division 3 on the scale ® indicates
300 m V . S i m i l a r l y , the other R A N G E selector positions
show their f u l l scale values.
(2) d B
Scale
In general, the dB values are expressed in d B V which
is a unit referenced by OdB equal to 1 V . T h e division
10 a t the scale ® corresponds to 0 dB on the dB scale,
which is a voltage r a t i o scale. Since the R A N G E
selector has 12 range positions in steps of 10 d B , the
voltage r a t i o of 0.3mV to 100V is 110dB attenuation.
Assume a reference voltage level on the scale @ be
1V w i t h the R A N G E selector a t "1 V," a given voltage
can be read as low a s - 7 0 d B ( 0 . 3 m V ) by turning the
selector d o w n w a r d . F u r t h e r , a s the scale ® a l l o w s
reading to - 2 0 d B ( 0 . 0 3 m V ) , you can continuously
measure the voltage r a t i o a s high a s - 9 0 d B ( 0 . 0 3 m V
to 1 V ) . The read of - 9 0 d B mea»~~ a signal-to-noise
- 9 -
r a t i o of around 1 0 d B . A l s o , the dB scale a l l o w s
continuous measuring up to +40dB(1 to 100V) by
turning the selector upward.
(3) d B m
Scale
In general, v o l t m e t e r s have a reference level division
of OdBm equal t o 0.775V ( 1 m W power) induced across
a 6 0 0 O resistance load. Therefore, the d B m scale is
a v a i l a b l e to measure a power level referenced to 0
d B m , w i t h the impedance of the given power c i r c u i t
being 6 0 0 O pure resistance. Where measured across
specific resistance loads, f o r example, 1 0 k O , other
t h a n the 6 0 0 O load, the levels are sometimes
expressed in d B s .
Figure 3 - Meter Scale Graduation
