Sect. li Page 2 Model 205AG
load, the Load Switch must be turned on, otllerwise
the OutputLevel M!ter andthe Attenuator indications
will not be correct. The Load Switch shoul,dbe oH
when the instrument is connected to loads within
the range of the line matching impedance!),
For example: with an OutputLevel Meter indication
of 40 volts and the output attenuators set at 40 db,
we find from Figure 2-1 that the true output voltage
into 600ohms would be 40 volts multiplied by 0. 01
or 0.4 volts. To convert this to a voltage across
a 200ohm matched load multiply by 0. 577or 0. 4 x
0. 577= 0.2308 volts.b. Turn the power switch to ONandallow ~pproxi-
mately five minutes for the instrument to stabi-
lize. Setthe Freq. ~nge control andthe frE~quency
dial sothat their indications whenmultiplied together
equal the desired frequency. For example: Fre-
quency dial indication 20, FREQUENCY RANGE
X100, 20x 100= 2000cycles/second.
2-4 INPUT LEVEL METER OPERATION
The Input Level meter is an independentaudio tre-
quencyvacuumtubevoltmeter, suitable for monitor -
ing the output voltage of a device under test. The
meter is calibrated involtsanddbabove 1 milliwatt
in 600ohms whenthe INPUT ATTENUATOR (DB)
switch is on zero.
c. Settheoutput attenuators and the AMPLrrUDE
control to obtain the desired outputlevel Dis-
tortion in the output will be minimized by I~eeping
the OutputLevel meter indication near maxim.umand
reducing the output with the output attenuators. When making comparative measurements across a
constant impedance the meter and INPUT ATTENU -
ATOR (DE) switch will indicate directly the change
in db in the circuit under test.
2-3 OUTPUT LEVEL METER OPERATION
The Output Level meter is calibrated directly in
output voltage and db above 1milliwatt when the
instrument is operating into a 600 ohm load and
both output attenuators are set at zero.
Whenusing the Input Level meter to monitor a 600
ohm circuit, the power level in db above 1 milli-
watt is equal to the meter indication plus the indi-
cation of the INPUT ATTENUATOR (DB) switch.
Whenmaking power measurements in circuits with
impedances below 600ohms, the absolute level in
db aboveor below 1 milliwatt is equal to the level
indicated onthe meter plus the INPUT ATTENU -
ATOR (DB) switch indication plus a correction
factor for the circuit impedance. Figure 2-2 gives
correction factors for impedances between 1 and
600ohms.
With any matchedload (50, 200, 600, or 500(]lohms)
the output power in db above or below 1milliwatt
is equal to the Output Level Meter indication less
the output attenuator settings. For examp,le: an
Output Level meter indication of +35db anda total
output attenuation of 45 db will produce an output
levelof -10 dbm into a matched load.
Figure 2-1 is a chart of meter voltage multiplying
factors for any value of output attenuation. With
the IM:PEDANCEswitch set at 600ohms andan in-
ternal or external 600ohm load, the output 1roltage
will be the Output Level meter voltage ind:ication
multiplied by a factor obtained from Figure 2-1
opposite the total output attenuation. For e~a.mple:
with the output attenuators set for 40 db aU Output
Level meter indications should be multiplied by
.01 to obtain the true output voltage into a 600ohm
load.
The input voltage level for any range of the INPUT
ATTENUATOR (DB) switch is thevoltage indicated
by the Input Level meter multiplied by the factor
indicated below for the particular range of the IN-
PUT ATTENUATOR (DB) switch in use.
To obtain the true output voltage into a 50, 200 or
5000ohm load the following factors must be~Lpplied
to the true voltage across a 600ohm matched load.
600 Ohm Voltage
Multiplying Faetor
Laad Impedance
50
200
5000
0.289
0.577
2.89
00090-2
