300w PA using a MRF300AN transistor by Sergey EX8MLE

300 watts 70 MHz linear power amplifier using an MRF300AN transistor

The power amplifier is designed to be used in amateur radio stations of 70 MHz band. The circuit is typical and does not require any explanations. RF chokes and matching networks coils are built on the PCB which makes this amplifier easy to replicate. It can be tuned to operate on the 50 MHz or 144 MHz band by changing the capacitors values and their connection points in Z1, Z2 matching networks. All the measurements of this amplifier parameters were made with the low-pass filter tuned for the 70 MHz band.

Please contact Sergey EX8MLE if you would like to buy an assembled PA or a PCB.

Parameters

Frequency Range – 70-72 MHz
Input/Output impedance – 50 ohms
Vdd = 50 V
Idq = 100 mA
Id = 7,2 A
Pin = 1,75 W single tone
Pout = 300 W CW
Gps = 22,3 dB
nD = 83%
Class – AB

Circuit diagram

Printed Circuit Board

Populated PCB

Low Pass Filter

Output Spectrum

Parts list

Part	Description	Part Number	Manufacturer
Q1	RF Power LDMOS Transistor	MRF300AN	NXP
PCB	FR4 1.6 mm 1 oz
C1	4700 pF Chip Capacitor	700B472KT50XT	ATC
C2	330 pF Chip Capacitor	100B331JT200XT	ATC
C3	56 pF Chip Capacitor	100B560KT500XT	ATC
C4	470 pF Chip Capacitor	100B471JT200XT	ATC
C5, C6	68 pF Chip Capacitor	100B680GW500XT	ATC
C7	100 pF Chip Capacitor	100B101JT500XT	ATC
C8	33 pF Chip Capacitor	100B330JT500XT	ATC
C9, 10	470 pF Chip Capacitor	100B471JT200XT	ATC
C11	1 n Chip Capacitor	1206C102KAT2A	Kyocera
C12, C15, C16	10 n Chip Capacitor	1206C103KAT2A	Kyocera
C13	100 n Chip Capacitor	1206C104KAT2A	Kyocera
C14	4.7 mF SMD Tantalum Capacitor	T491B475M016AS	KEMET
C17, C18, C19, C20, C21, C22	1 n Chip Capacitor	100B102JT50XT	ATC
C23	10 n Chip Capacitor	1812B103K302NT	Walsin Technology
C24	220 mF, 63 V Electrolytic Capacitor	CE1J221M1XANG	Sanyo
D1	5.1 V Zener Diode	BZV55C5V1-TP	MCC
D2	1SS355VMFH	1SS355VMFHTE-17	ROHM
R1, R2	Ω 2512	RC2512FK-0710R	YAGEO
R3	Ω 2512	RC2512JK-07100R	YAGEO
R4	kΩ 0805	RC0805JR-072K2	YAGEO
R5	1 kΩ 0805	RC0805FR-071K	YAGEO
R6	10 kΩ Thermistor	NTC-MF52-103F3435	Shenzhen Haiwang Sensor
R7	22 kΩ 1206	RC1206FR-0722K	YAGEO
R8	4.7 kΩ 1206	RC1206FR-074K7	YAGEO
R9	5 kΩ	3292W-1-502LF	BOURNS
R10	10 Ω 1206	RC1206FR-0710R	YAGEO
L1, L2	See text circuit diagram
Z1, Z2	See text circuit diagram