Model 618B Sect.IV Page 17
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PART 1 - REPLACING ATTEI? JATOR PROBE 8) Remount RF OUTPUT connector. Tighten
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cable clamp.
Power from the resonator is coupled to the RF
OUTPUT jack at the front panel through an as- 9) After the assembly is replaced, an error of
,. sembly consisting of the panel jack, a length of a few decibels may exist in the calibration of the
RG-55/U cable, and the attenuator probe. The attenuator dial.
attenuator probe is terminated by a special re-
sistor, R203, which is made by coating platinum
on a glass bead. This resistor should normally
last for the life of the equipment even if subject PART 2 - ATTENUATOR DIAL ALIGNMENT
to shock and vibration.
1) The following equipment- will be required for
Should the resistor become broken or otherwise this operation:
defective however, the complete attenuator as-
sembly must be replaced. The stock number for a. An @ Model 4778 Thermistor Mount or
this assembly is listed in the Table of Replaceable equivalent. The @ Model G485B Detector
Parts (Section V). Mount and G281A Waveguide to Coax Adapter
plus the @ Model J485B Detector Mount and
J281A Waveguide to Coax Adapter can also
If the glass bead becomes broken, the following two be used.
symptoms will usually be present:
b. An @ Model 430C Microwave Power Meter.
- No rf output will be obtained, or will be obtained
with erratic frequency response. 2) Connect rf power meter such as @ Model 430C
to output end of output cable by means of a ther-
- The dc resistance between the center pin of the mistor mount such as @ Model 477B. The @ -
RF OUTPUT connector and ground will be very .. Model G485B Detector Mount and G281A Wave-
large. guide to Coax Adapter can be used from 3800 to
5850 mc. The @ Model J485B Detector Mount
and J281A Waveguide to Coax Adapter can be used
Replace a defective attenuator assembly as follows: from 5850 to 7600 mc.
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1) Remove the four screws holding the RF OUT- 3) Turn signal generator on and allow a 20 minute
PUT connector to the front panel. warm up period with modulation selector switch
in CW position.
2) Release attenuator cable from under cable
4) Turn modulation selector switch to OFF po-
clamp.
sition, adjust zero set controls in generator and
power meter to zero, and return modulation se-
3) Remove mounting screw which holds the rack lector switch to CW position. To prevent drift
to the aluminum block on the attenuator probe.
due to temperature change make these adjustments
as quickly as possible.
4) Lift mounting block and probe from the cir-
cular waveguide housing. 5) Tune signal generator to 3800 MC and adjust
power set control for zero dbm indication on power
5) Use care in handling attenuator probes. The set meter in generator.
glass bead resistor can be broken by twisting the
cable. Mounting block comes affixed to new probe. 6) Adjust detector mount for maximum reading
on power meter with generator output attenuator
set to 7 (-7 dbm). Record frequency and external
6) Insert new probe into the waveguide only as far
power meter reading. If the 477B Thermistor
as is necessary to match up the block mounting
mount is used, no adjustment of the detectormount
holds. Insert mounting screw and tighten. will be required.
7) Carefully thread cable under cable clampand 7) Repeat step 6 every 200 mc across entire fre-
around casting to front panel. Avoid twisting quency range. Change detector mount and adaptor
cable more than one-quarter turn. as explained in step 2 at 5850 mc. |
ACEC
