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G8MNY > TECH 02.04.04 12:18l 35 Lines 1267 Bytes #999 (0) @ WW
BID : 51175_GB7CIP
Read: DB0FHN GUEST OE7FMI
Subj: Transistor PA Biasing
Path: DB0FHN<DB0RGB<OK0PPL<DB0RES<ON0AR<WB0TAX<ZL2TZE<GB7YFS<GB7CIP
Sent: 040402/0959Z @:GB7CIP.#32.GBR.EU #:51175 [Caterham] $:51175_GB7CIP
From: G8MNY@GB7CIP.#32.GBR.EU
To : TECH@WW
By G8MNY (graphics updated 11/03)
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. TR1 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. TR2 needs heat sinking so it
is also convenient to mount it on close to TR1.
Bias adjustment can be done by adjusting the 1K but never change it just for a
preset without a safe minimum series R!
The MAX base current, about 500mA is available, this is limited by the 22R &
should be enough current for a 50W UHF/VHF or 100W HF PA.
PTT
Switched
+12V ÄÂÄÄÄÂÄÄÄÄÄÄÄÄÄÄ¿
³ ³ 22R 10W
³ 1K NPN ³
10u ³+ ³ TR2³/c
=== ÃÄÄÄÄÄÄÄÄ´TIP
³ ³ ³\e +570mV
³ ³ TR1 ÃÄÄÄÄÂÄÄÄÂÄÄÄ RFC to PA
³ c\³ ³ ³ ³ Bases
³ ÃÄÄÄFBÄÄÄ´ ³ +³
³ e/³ NPN 5R6 === ===
³ ³ ³ 1n³ ³10u
0V ÄÄÄÁÄÄÄÁÄÄÄÄÄÄÄÄÄÄÁÄÄÄÄÁÄÄÄÁÄÄÄÄ
/QSL
73 De John, G8MNY @ GB7CIP
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