BEXT PJ 250 - Recommended Test Equipment; Maintenance and Adjustments

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This module is composed of a board shielded by a metal box mounted on the left side near the rear panel,
as shown in Fig.3. on this board, the electronics detect any system anomaly such as excessive SWR,
internal or antenna, over-temperature or overdrive, This module will also, whenever possible, reset the
system to its original conditions, after a fault has occurred.
RF POWER AMPLIFIER
The module is placed in the upper right side of the amplifier. This module is totally shielded and placed
on a heat sink (see Fig.3). This circuit delivers 300W with 25-30W of drive and is supplied by a dedicated
power supply. The quiescent parameters of each module are:
Vdc=28V Ia=15A Pout=250 W
The active devices employed are BJT NPN MOTOROLA (MRF317).
LOW PASS FILTER
This filter is fitted in a metallic box mounted on the heat sink on the right position as shown in Fig.3.
Thanks to this low pass filter the harmonic suppression is greater than 75 dBm.
DIRECTIONAL COUPLER
This circuit is placed on the upper right side of the amplifier and fitted on the rear panel as shown in
Fig.3. This module makes the measurement of the forward and reflected power.
RECOMMENDED TEST EQUIPMENT
INSTRUMENT TYPE SUGGESTED MODEL CRITICAL SPECIFICATIONS
Non Inductive Bird 50 ohm P > 250 W
Dummy Load
Spectrum Analyzer Advantest 10KHz-3.5GHz
MOD. R4131D
FM Monitoring R/S
Demodulator MOD. F.A.M.
Digital Multimeter MOD. Metrix
Calibrated in-line Bird MOD. 43 50 ohm
Wattmeter with Sample
Exciter BEXT Frequency 87.5-108MHz
MOD TEX 30 Pout from 2W to 30W
Dummy Load 25 ohm P 500W
MAINTENANCE
INTRODUCTION
The following section provides general maintenance information and electrical adjustment procedures for
the PJ250 Amplifier. Maintenance is divided into categories dependent upon the complexity of the
procedure and the test equipment required to complete the maintenance.