Principles Of Operation - HP 8481H 8482H Operating And Service Manual

HP 8481H/82H
Service
Table 6. Code list of Manufacturers
Mfr
Code
Manufacturer Name
Address Zip Code
00000
ANY SATISFACTORY SUPPLIER
00S43 HOFFMAN ENG CO DIV OF FED CARTRIDGE
ANOKA MN 55303
01686 RCL ELECTRONICS INC
NORTHBROOK IL US 60062
01766 INTL CRYSTAL MFG CO INC
OKLAHOMA CITY OK
73102
0S876
U S POLYMERIC INC
STAMFORD
CT 06904
06383 PANDUIT CORP TINLEY PARK
IL US
60477
09969 DALE ELECTRONICS INC
YANKTON SD US 57078
12344 TALLY CORP
KENT UA 98031
12498 CRYSTAL0NICS, DIV TELEDYNE
CAMBRIDGE MA 02140
1970! MEPC0/CENTRALA8 INC RIVIERA
FL US 33404
28480 HEWLETT-PACKARD CO CORPORATE HO
PALO ALTO CA 94304
46384
PENN ENGINEERING
&
MFG CORP
D0YLEST0UN PA US
18901
84830
LEE SPRING CO BROOKLYN NY US
11219
Principles
Of
Operation
Bulkhead assembly A1 presents a 50-ohm load to the RF signal
applied to the power sensor. The RF signal absorbed by the
thermocouples generates a dc voltage that is proportional to the RF
input power.
Components A.2E1 and A.2E2 are ferrite beads situated in the black
plastic block through which the wires from Al pass to A2-. Each
ferrite bead increases the self-inductance of the wire passing through
the bead, causing this portion of wire to act as an RF choke. The
result is to minimize RF feedthrough to the A2 input amplifier
assembly.
The dc output from the bulkhead assembly is applied to the two
field-effect transistors (FE-T's) in A2U1. These transistors function as
a sampling gate (or chopper). The sampling rate .is controlled by a
220 Hz square wave supplied by the power meter. The sampling gate
output (at pin 3 of A2U1) is a 220 Hz square wa.ve having a voltage
proportional to the RF power input.
The output of A2U1 is amplified about 700 times by an operational
amplifier made up of A2Q1 and the first amplifier stage in the power
meter. Figure 4 is a simplified diagram of the complete operational
amplifier.
15