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G8MNY > TECH 08.04.12 09:39l 39 Lines 1348 Bytes #999 (0) @ WW
BID : 30521_GB7CIP
Read: GUEST
Subj: Transistor PA Biasing
Path: IZ3LSV<IK2XDE<DB0RES<ON0AR<UA6ADV<GB7CIP
Sent: 120407/2240Z @:GB7CIP.#32.GBR.EU #:30521 [Caterham Surrey GBR] $:30521_GB
From: G8MNY@GB7CIP.#32.GBR.EU
To : TECH@WW
By G8MNY (Updated Aug 07)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
Here is a simple circuit that can deliver the peak base current needed for
linear SSB operation, that works very well. It uses 2 TIP type NPN transistors,
3 Rs, & suitable RF filtering for the band in use. T1 must be bolted close to
the PA devices so that it's emitter base voltage can tracks the PA temperature,
the base is protected from RF with a ferrite bead. T2 needs heat sinking so it
is also convenient to mount it on close to T1.
Bias adjustment can be done by adjusting the 470R but never change it just for
a preset without a safe minimum series R!
The MAX base current, about 1A is available, this is limited by the 10R &
should be enough current for a 50W UHF or 100W VHF or 200W HF PA.
PTT
Switched
+12V ÄÂÄÄÄÂÄÄÄÄÄÄÄÄÄÄ¿
³ ³ 10R 10W
³ 470R NPN ³
10u ³+ ³ T2³/c
=== ÃÄÄÄÄÄÄÄÄ´TIP
³ ³ ³\e +570mV
³ ³ T1 ÃÄÄÄÄÂÄÄÄÂÄÄÄ RFC to PA
³ c\³ ³ ³ ³ Bases
³ ÃÄÄFBÄÄÄÄ´ ³ +³
³ e/³ NPN 5R6 === ===
³ ³ ³ 1n³ ³10u
0V ÄÄÄÁÄÄÄÁÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÁÄÄÄÁÄÄÄÄ
Why Don't U send an interesting bul?
73 De John, G8MNY @ GB7CIP
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