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G8MNY > TECH 14.07.03 23:49l 43 Lines 1743 Bytes #999 (0) @ WW
BID : 5665_GB7CIP
Read: DB0FHN GUEST OE7FMI
Subj: DC/RF Sensing PA Switching
Path: DB0FHN<DB0RGB<DB0MRW<OK0PKL<OK0PPL<RZ6HXA<HA3PG<DK0WUE<GB7FCR<GB7CRV<
GB7CIP
Sent: 030714/2010Z @:GB7CIP.#32.GBR.EU #:5665 [Caterham] $:5665_GB7CIP
From: G8MNY@GB7CIP.#32.GBR.EU
To : TECH@WW
For PA with RF/DC sense switching (as some rigs put out DC on Tx), that used a
diode to detect any +ve signals (RF/DC) on the transceiver to operate the PA
PTT system....
The time constants are ok for SSB & FM, but 22uF can be omitted for FM only.
TR1 & 2 BC107 etc, TR3 a TIP type PNP, D1 rf diode 1N4148 etc, D2 1N4001.
HOW IT WORKS
D1 detects RF & passes any DC to turn on TR1. TR1 turning on charges up the
22uF & makes TR3 initially conduct to give fast Tx attack. When 22uF is over
2V TR2 is turned on & passes higher base current into TR3 via a Tx LED ensuring
it is well turned on. The 150K +ve feedback ensure snap action.
External PTT earth can be put in/out on TR2 collector.
1n
Rig -------!!----> RF to Drive Relay
! !
100K _!_
! \ /D1 ___________+12-24V
! --- !/e
! ! .----------------------------! TR3
! ! ! ! !\
! ! ! Ext o__ 330 !
! 22K !/ PTT ! LED ! !___________Drive, O/P
! !----! TR1 !----!<!--- ! Power & Fan
! ! !\e !/ ! Relays
! === !--47K------! TR2 !
! !10n !+ ! !\e !
! ! === !------)----150K--------!
! ! !22u ! ! _!_
! ! ! 10K ! /_\ D2
! ! ! ! ! !
--------------------------------------------------
I have found it was heat sensitive, due to the sensitivity of the 1st NPN.
/QSL
73 De John, G8MNY @ GB7CIP
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