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2.6.11 dB Applications
2.7 DMM SETUP PROGRAMS
Measuring
Circuit Gain/Loss-Any
point in a circuit can
be established
as the OdB point. Measurements
in that cir-
cuit are then referenced
to that point expressed
in terms
of gain (+dB) or loss (-dB).
To set the zero dB point pm-
teed as follows:
There are eight DMM setup programs available from the
front panel of the Model 199, as summarized
in Table 2-6.
These programs
are described
in detail in the following
paragraphs.
1. Place the Model 199 in AC volts and dB.
2. Connect
the Model 199 to the desired location
in the
circuit.
3. Press the ZERO button. The display will read OdB.
4. Gainlloss
measurements
can now be made referenced
to the OdB point.
Program Selection-Programs
can be selected by pressing
SHIFT DMM SETUP on the front panel. To scroll through
programs, press the NEXT key. Once the desired program
is displayed, perform the necessary operation, as described
below.
Measuring
Bandwidth-The
Model 199 can be used to
determine
the bandwidth
of an amplifier
as follows:
1. Connect a signal generator and a frequency
counter to
the input of the amplifier.
Data Entry-The
IEEE-488 primary
address program re-
quires numeric data entry. To enter data, use the data en-
try keys (O-9). The cursor location for data entry is indicated
by the bright, flashing display digit. The cursor moves right
each time a number
is entered.
The cursor will wrap
around to the left after exiting the right most digit. When
the desired value is displayed,
press SHIFf
to program
the value.
2. Set the Model 199 to AC v&s
and autorange.
3. Connect
the Model 199 to the load of the amplifier.
4. Adjust the frequency of the signal generat& until ape+
AC voltage reading is measured on the Model 199. This
is the center frequency.
Alternate
Condition
Selection-Most
DMM setup pro-
grams have a&mate
conditions
that can be selected.
TO
toggle the conditiop,
press uprange or dowmange to alter-
nate between
the the two selections.
5. Press SHIFT dB button and then press the ZERO but-
ton. The OdB point is now established.
6. Increase the frequency input until the Model 199 reads
-3.OOdB. The frequency
measured
on the frequency
counter is the high-end
limit of the bandwidth.
7. Decrease the frequency input until the dB reading again
falls to -3.OOdB. The frequency measured on the signal
generator
is the low-end limit of the bandwidth.
Exiting
DMM
Setup-To
exit DMM
setups,
repeatedly
press NEXT and scroll through the complete
list in the
UlH-l".
Table 2-6. DMM Setup Programs
Note: The bandwidth
of the Model
199 is typically
3CKlkHz. Do not use this application to check amplifiers
that exceed the bandwidth
of the Model 199.
/ Program Description
Determining
Q-The
Q of a tuned circuit can be deter-
mined as follows:
1. Determine
the center frequency
and bandwidth
as ex-
plained
in
the
previous
application
(Measuring
Bandwidth).
Software
revision level
Multiplexer
on/off
IEEE Primary Address
Line frequency
(50 or 6OHz)
Save instrumerit
setups
2. Calculate
Q by using the following formula:
Q = Center Frequency/Bandwidth
Reset instrument
REV.A0.66+'
MUX ON
26 IEEE*
FREQ=6OHz'
SAVE NO
LEDS OFF
DEBUG
OFF
RESET NO
*Factory default values shown. 6Oti
is default in the U.S.
O=lY
Display Message
upon Entry
J
"Revision
level may vary.
2-16
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