Operation - HP AR Operating And Servicing Manual

output must be kept away from the input to avoid the possibility of
feedback.
2-4 OPERATION
The input circuit of the Model 460AR is a terminated transmission
line with a characteristic impedance of 200 ohms.
The output circuit has an impedance of 280 ohms (resistive). The
load impedance determines the gain of the amplifier. Therefore.
it is not neces sary to match the load to the output of the amplifier
unless the gain is adversely affected. Shown below are two dia-
grams for connecting a matched or unmatched load to the Model
460AR using a 200 ohm cable.
Connect acros s output Jack
inside instrument
200
ohms
load
,-,
4'-----+/-'
.-0--'- - - - - ,
Model 460AR
OUTPUT
~~~----'
-L"""
200 ohm cable
<
,
,
\
•
j
,
,
620 To any
ohms
load
Model 460AR
OUTPUT
200 ohm
cable
The GAIN control will vary the gain of the amplifier over a range
of approximately 6 db. This control is provided so that the gain
of the amplifier can be set to a known value if nec-es sary.
There
is no feedback in the amplifier. so the gain is directly proportional
to the Gm of the tubes. The gain is also determined by the output
load and will vary with output load in accordance with the relation
280 X ZL
280
+
ZL
The Wide Band Amplifier can be used with the <$Model 410 Vacu-
um Tube Voltmeter to provide additional sensitivity in measuring
high frequencies. A special adaptor is available to connect the
probe of the Model 410 to the output terminal of the amplifier.
The overall frequency response of the Model 460AR. in combina-
tion with the Model 410. is within 1 db out to 190 me. This combi-
nation will give a full scale meter reading on the Model 410 with
1/10 volt applied to the input of the Model 460AR.
-4-