Assembly Instructions Chapter 4

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LX Series Power Amplifier Assembly Chapter 4, Circuit Descriptions

LX Series, Rev. 0 4-1

Chapter 4

Circuit Descriptions

The RF from the exciter/driver assembly

connects from the RF Output “N” Jack J25,

through a RG-55 cable, to the PA RF Input

SMA Jack J200, located on the rear of the

PA chassis assembly. The RF Input is

cabled through UT-141 to port J111 on

the main chassis. Jack J1 on the PA

module assembly connects to the J111

port when the module assembly is slid

into place.

The RF output from the 2 way UHF

combiner connects to the PA RF Output

Jack J2, located on the rear of the PA

Module. Jack J2 on the PA module

connects to the J115 port, on the main

chassis assembly, when the module

assembly is slid into place.

4.1 (A4) Power Amplifier Module

Assembly (1302868; Appendix B)

The Power Amplifier Module Assembly

contains (A1) a UHF Phase/Gain Board

(1303213), (A2) a 150W Driver Pallet,

Dual Output (1303293), (A3 & A4) UHF

RF Module Pallet Assemblies (1300116),

(A5) a 2 Way UHF Combiner Assembly

(1303208), (A6) an Amplifier Control

Board (1301962) and (A7) a

Temperature Sensor IC.

4.1.1 (A1) UHF Phase/Gain Board

(1303213; Appendix B)

The RF input from J1 on the PA assembly

connects to J1 on the Phase/Gain Board.

The UHF phase/gain board provides the

circuits that adjust the gain and the

phase of the RF signal for the PA

amplifier assembly in which it is

mounted. The input signal connects to

the gain circuit through the capacitor

C13. The gain circuit consists of U1,

R16, CR4, R22, R17, CR5, R23, R27 and

the gain pot, R25. U1 is a 90°, 2-way

splitter. The signal at pin 1 of U1 is split

and applied to pins 3 and 4. The signal

reflects off CR4 and CR5 and is passed to

pin 2. The gain between pins 1 and 2

changes with the voltage applied across

CR4 and CR5. This voltage is controlled by

the gain-adjust pot R25. The more

positive the voltage, the more the diodes

CR4 and CR5 conduct therefore the less

gain through the circuit. The gain

controlled output is coupled through C14

and the pi-type divider circuit consisting of

R8, R5 and R9 that drops the level before it

applied to the phase-shifter circuit.

The level controlled signal connects to the

phase-shifter circuit that consists of U2,

C20, C21, CR2, and CR3. U2 is a 90°, 2-

way splitter. The signal at pin 1 of U2 is

split and applied to pins 3 and 4. The signal

reflects off CR2 and CR3 and is passed to

pin 2. The phase shift between pins 1 and

2 changes with the voltage applied across

CR2 and CR3. This voltage is controlled by

the phase-adjust pot R24 through R26,

R18 and R19. +12 VDC from an external

switching power supply is applied to J3 on

the board and is used as the reference that

is applied to the phase-control pot. The

gain and phase controlled output connects

to J2 on the board.

4.1.2 (A2) 150 Watt Driver Pallet

Assembly, Dual Output (1303293;

Appendix B)

The output of the Phase/Gain Board is

connected to the input J1 of (A2) the 150

Watt UHF amplifier assembly. The

assembly contains a 150 Watt CW UHF

Driver Board, Dual Output (1303169).

4.1.3 150 Watt Driver, Dual Output

(1303169; Appendix B)

The board operates class AB and is a

highly linear broadband amplifier for the

frequency range of 470 to 860 MHz. It can

deliver an output power of 150 watts

(CW) with approximately 14 dB of gain.

Summary of content (5 pages)

PAGE 1
LX Series Power Amplifier Assembly Chapter 4, Circuit Descriptions Chapter 4 Circuit Descriptions The RF from the exciter/driver assembly connects from the RF Output “N” Jack J25, through a RG-55 cable, to the PA RF Input SMA Jack J200, located on the rear of the PA chassis assembly. The RF Input is cabled through UT-141 to port J111 on the main chassis. Jack J1 on the PA module assembly connects to the J111 port when the module assembly is slid into place.
PAGE 2
LX Series Power Amplifier Assembly Chapter 4, Circuit Descriptions The amplification circuit consists of LDMOS transistors Q1 and Q2 connected in parallel and operating class AB. The paralleling network is achieved with the aid of 3 dB couplers U3 and U4. The quiescent current settings are achieved by means of potentiometers R6 and R10. C39 and C38 are adjusted for best response. The settings are factory implemented and should not be altered.
PAGE 3
LX Series Power Amplifier Assembly 4.1.6 (A5) Amplifier Control Board (1301962; Appendix B) The amplifier control board provides LED fault and enable indications on the front panel of the module and also performs the following functions: overdrive cutback, when the drive level reaches the amount needed to attain 110% output power; and overtemperature, VSWR, and overdrive faults.
PAGE 4
LX Series Power Amplifier Assembly amplifier U17 or U18 at high current shut down should be greater than 15 Amps. U14B is used to turn Off the gate of Q10 in the event of high power supply voltage, approximately +35.4 VDC. U14A is used to keep the FET disabled in the event of low power supply voltage, approximately +25.4 VDC. Current monitoring sections of the board. The ICs U16, U17 and U18 along with associated components set up the current monitoring sections of the board. R67, R68 and R69 are 0.
PAGE 5
LX Series Power Amplifier Assembly and connected to the Reflected Power Shutdown circuit at CR28. The low shuts off Q14 causing pin 3 to go high that is connected to the inverter U15C. The output of U15C goes low producing a Reflected Power Fault that is connected to an output of the board, the Fault Alert circuit and also shuts down Amplifier #1. Gain of the power measurements is completed through software. Only the Aural Null and Offset Null need to be done through front panel pots.