Tektronix 492 Operator's Handbook

ATTEN dB and MIN NOISE / MIN DISTORTION selectors .
The microcomputer assumes the MIN RF ATTEN dB
selection is the minimum attenuation required for the
expected signal
levels . It does
not
reduce RF
attenuation
below this value . It also selects the best ratio of RF
attenuation and IF gain according to the MIN NOISE / MIN
DISTORTION mode ( see description that follows ) . MIN
RF ATTEN selects the lower limit reference level range . As
MIN RF ATTEN dB is increased , the lower limit reference
level is raised an equal amount . At dB minimum
attenuation , the lower limit reference level is -123 dBm .
At 10 dBm minimum attenuation , the reference level goes
to 113 dBm
, etc.
The reference level increments depend on the Vertical
Display mode and FINE selector mode . Reference level
steps for the log displays are 10 dB and 1 dB with FINE off ,
and 1 dB and 0.25 dB with FINE activated ( 0.25 dB steps
apply to the AA mode ) . For LIN displays with FINE off , the
microcomputer
selects
the
reference level
, which is
the
equivalent
of an 8 -
division
signal ,
where
the
bottom of
the
crt graticule is zero volts and the top of the crt graticule is
eight times the vertical display factor . The display factor
changes in a 1-2-5 volts / division sequence . For LIN
displays with FINE on , the reference level changes in 1 dB
steps and the scale factor is 1/8 the voltage equivalent of
the reference level .
DELTA A MODE
To select this mode , activate 2 dB / DIV and FINE ; the
REF LEVEL readout becomes * 0.00 dB and the
REFERENCE LEVEL steps in 0.25 dB increments .
The AA mode is useful for measuring relative amplitude
differences of signals more accurately . This is because the
gain distribution ( IF gain and RF attenuation ) is not
changed when
AA mode
is
activated . The REF
LEVEL
is
changed by
shifting the
log amplifier
offset . The
measure
ment
range
of the AA mode
is at least
from 10 dB
above
to
40 dB below the reference level established when the
mode was activated ; however , the overall instrument
display characteristic of -123 dBm to +30 dBm cannot be
exceeded . The asterisk in the REF LEVEL readout remains
until the AA mode gain distribution is changed .
The AA mode is canceled when either FINE or
2 dB / DIV are deactivated , or a selector that could change
gain
distribution ( MIN
RF
ATTEN or MIN
NOISE ) is
changed .
The
analyzer also
deactivates
AA
mode
when
EXT MIXER or an external mixer frequency range is
selected
.
492
Operator's
Handbook
3-7

Tektronix 492 Specifications

General

Brand	Tektronix
Model	492
Category	Measuring Instruments
Language	English