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3RF Application Reports

300-Watt Linear Amplifier Schematic Diagram

C1 — 100 pF

C2, C3 — 5600 pF

C4, C5 — 680 pF

C6, C7 — 0.10 µF

C11 — 470 pF

C12, C13 — 0.33 µF

C14 — 10 µF – 50 V electrolytic

C15 — 500 µF – 3 V electrolytic

C16 — 1000 pF

R1, R2 — 2 x 3.3 Ω, 1/2 W in parallel

R3, R4 — 2 x 3.9 Ω, 1/2 W in parallel

R5 — 47 Ω, 5 W

R6 — 1.0 Ω, 1/2 W

R7, R8 — 1.0 k, 1/2 W

R9 — 18 k, 1/2 W

R10 — 8.2 k, 1/2 W

R11 — 1.0 k Trimpot

D1 — 2N5190

L1, L2 — Ferroxcube VK200 20/4B

L3, L4 — 6 ferrite beads each,

Ferroxcube 56590 65/3B

Q1, Q2 — MRF422,

Q3 — 2N5990

T1, T2, T3 — See text

All capacitors except electrolytics and C16

are chips —

Union Carbide type 1813 and 1225, or

Varadyne size 18 or 14, or equivalent

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For production quantities, the braid in T

may be made

of brass or copper tubes with their ends soldered to pieces

of PC board laminate. See cover picture and Motorola

AN-749 for details.

The bandwidth characteristics of these transformers do

not equal those of the transmission line type, but they’re

much easier to duplicate.

The measured performance of the amplifier is shown in

figures 1, 2, and 3 and harmonic rejection data in table 1.

* A similar product is available from Fair-Rite Products Corp., Wallkill,

N.Y.,12589

Registered trademark of DuPont

PCB, chips capacitors, transformers T

, T

, and ferrite beads

are available from: COMMUNICATIONS CONCEPTS, 2648 N. Ara-

gon Ave., Kettering, Ohio 45420. Telephone: (513) 294-8425.

Table 1. Output Harmonic Contents,

Measured at 300-W CW

(all test data taken using a tuned output,

narrow band signal source).

2nd 3rd 4th 5th

f (Mhz) (dB below the carrier)

30.0 – 38 – 25 – 34 – 48

20.0 – 33 – 13 – 43 – 45

15.0 – 50 – 10 – 51 – 47

7.5 – 40 – 30 – 55 – 47

4.0 – 37 – 22 – 55 – 37

2.0 – 36 – 18 – 45 – 37

1 2 3 4 5

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