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G8MNY > TECH 14.07.03 23:48l 31 Lines 1125 Bytes #999 (0) @ WW
BID : 5664_GB7CIP
Read: DB0FHN GUEST OE7FMI
Subj: Transistor PA Biasing
Path: DB0FHN<DB0RGB<DB0MRW<OK0PKL<OK0PPL<RZ6HXA<HA3PG<DK0WUE<GB7FCR<GB7CRV<
GB7CIP
Sent: 030714/1955Z @:GB7CIP.#32.GBR.EU #:5664 [Caterham] $:5664_GB7CIP
From: G8MNY@GB7CIP.#32.GBR.EU
To : TECH@WW
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 track the PA temperature,
TR2 needs heatsinking so it is also convenient to mount it close to TR1. Bias
adjustment can be done by adjusting the 1K but never change it just for a
preset without a min 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 --------------------
! ! !
! ! 22R 10W
! 1K !
10u ! ! !/c
=== !-----------!
! ! TR2 !\e +570mV
! c\! TR1 !----------RFC to PA
! !-----------! ! ! Bases
! e/! 5R6 === ===
! ! ! 1n! ! 10u
0V -------------------------------
/QSL
73 De John, G8MNY @ GB7CIP
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