Communication-concepts EB27A Engineering Bulletin User Manual download pdf

ARCHIVE INFORMATION

1RF Application Reports

GET 300 WATTS PEP LINEAR ACROSS 2 TO 30 MHz

FROM THIS PUSH-PULL AMPLIFIER

Prepared by: Helge Granberg

Circuits Engineer, SSB

(The heat sink shown with amplifier is sufficient only for short test periods under forced air cooling.)

This bulletin supplies sufficient information to build a

push-pull linear amplifier for 300 watts of PEP or CW output

power across the 2- to 30-MHz band. One of Motorola’s new

high-power transistors developed for single-sideband,

MRF422, is used in this application.

Like all transistors in its family of devices, MRF422

combines single-chip construction that is advancing the

state-of-the-art, and improved packaging to accommodate

the low collector efficiencies encountered in class B

operation. Rated maximum output power is 150 watts CW

or PEP with intermodulation distortion spec’d at – 30 dB

maximum, – 33 dB typical. Although not recommended, a

saturated power level of 240- to 250-W is achievable.

Maximum allowable dissipation is 300 W at 25°C.

Because of its excellent load and line voltage regulating

capabilities, an integrated circuit bias regulator is used in the

amplifier. The MPC1000, originally described in this bulletin,

consisted of a MC1723 chip and a built-in pass transistor.

The manufacture of this device has been discontinued

however, and the board lay-out was modified to incorporate

the above two in separate packages. The load regulation

typically measures less than 2% at current levels up to 0.5

A, which assumes an h

of 40 for the RF power devices.

The board surface provides a sufficient heat sink for the

2N5990 pass transistor, but a separate heat dissipator, such

as Thermalloy 6107 can be added if necessary. With the

component values shown, the bias is adjustable from 0.4

to 0.8 volts.

Gain flatness over the band is achieved using base input

networks R

and R

and negative feedback through R

and R

. The networks represent a series reactance of 0.69

ohms at 30 MHz rising to 1.48 ohms at 2 MHz. A single-turn

winding in the collector choke provides a low-impedance

negative feedback source, thus R

and R

determine the

amount. The reactance of C

reduces feedback at high

frequencies with the result that feedback increases an

average of 4 dB per octave at decreasing frequency.

MOTOROLA

SEMICONDUCTOR

Order this document

by EB27A/D



 Motorola, Inc. 1993

EB27A

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ARCHIVE INFORMATION 1

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Page 1 - ARCHIVE INFORMATION

ARCHIVE INFORMATIONARCHIVE INFORMATION1RF Application ReportsGET 300 WATTS PEP LINEAR ACROSS 2 TO 30 MHzFROM THIS PUSH-PULL AMPLIFIERPrepared by: Helg

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ARCHIVE INFORMATIONARCHIVE INFORMATION2 RF Application ReportsTransformer ConstructionFor continuous operation at full power CW, it isrecommended

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ARCHIVE INFORMATIONARCHIVE INFORMATION3RF Application Reports300-Watt Linear Amplifier Schematic DiagramC1 — 100 pFC2, C3 — 5600 pFC4, C5 — 680 p

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ARCHIVE INFORMATIONARCHIVE INFORMATION4 RF Application ReportsNOTE: Not to Scale           

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ARCHIVE INFORMATIONARCHIVE INFORMATION5RF Application ReportsMotorola reserves the right to make changes without further notice to any products h

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