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G8MNY > TECH 27.02.26 17:11l 64 Lines 3156 Bytes #10 (0) @ WW
BID : 53154_GB7CIP
Subj: A Simple V.O.X. Circuit
Path: JH4XSY<N3HYM<GB7YEW<GB7CIP
Sent: 260227/0810Z @:GB7CIP.#32.GBR.EURO #:53154 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (Updated Sep 09)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
Here is a 3 transistors 6 diodes circuit that is a Voice Operated Tx PTT
control as well as an ANTI VOX circuit to stop mis-operation from Rx noise.
SCHEMATIC
ﾚﾄﾄﾄﾄﾄﾄｿﾚﾄﾄﾄｿﾚﾄﾄﾄﾄﾄﾄﾄﾄｿﾚﾄﾄﾄﾄﾄﾄﾄﾄﾄｿﾚﾄﾄﾄﾄﾄｿﾚﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄｿﾚﾄﾄﾄﾄﾄｿﾚﾄﾄﾄﾄﾄﾄﾄﾄｿ
>ﾄｴ RFI ﾃｴMICﾃｴ AF ﾃｴSet Decayﾃｴ Set ﾃｴ LEVEL ﾃｴ Set ﾃｴ AF ﾃﾄ<Rx
MicｳFilterｳｳAMPｳｳDETECTORｳｳ Time ｳｳLevelｳｳCOMPARITORｳｳLevelｳｳDETECTORｳ LS
In ﾀﾄﾄﾄﾄﾄﾄﾙﾀﾄﾄﾄﾙﾀﾄﾄﾄﾄﾄﾄﾄﾄﾙﾀﾄﾄﾄﾄﾄﾄﾄﾄﾄﾙﾀﾄﾄﾄﾄﾄﾙﾀﾄﾄﾄﾄﾄﾂﾄﾄﾄﾄﾙﾀﾄﾄﾄﾄﾄﾙﾀﾄﾄﾄﾄﾄﾄﾄﾄﾙ
ﾚﾄﾄﾄﾄﾄﾁﾄﾄﾄﾄｿ
ｳPTT DRIVERﾃﾄﾄ>PTT
ﾀﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾙ
CIRCUIT
VOX TIME VOX GAIN ANTI VOX Smooth
+ﾚﾄﾄﾄﾄﾄﾂﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾂﾄﾄﾂﾄﾄﾄﾂﾄﾄﾄﾄﾂﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾂﾄﾄﾄﾂﾄﾄﾄﾄﾄﾂﾄﾄﾄﾄﾄﾄﾄﾄﾄ<+9-15V
100u === _ｳ_ 2uFｳ+ ｳ ｳ ｳ ｳ +ｳ10u _ｳ_
_ｳ_ D1\_/ === ｳ 220K ｳ ﾚﾄ>10K === /_\ D5
ﾃﾄﾄﾄﾄｿ ｳ === VAR ｳ PNPｳ/e POT ｳ ｳ
ｳ Ge_ｳ_D2 10K ｳu1 ｳ 220K<ﾄﾄﾂﾄﾄｴ ｳ ｳ D4 ｳ+10u
10K /_\ Geｳ ｳ ｳ POT ｳ ｳ\ ﾀﾄﾄﾄﾁﾄｴ>ﾃﾄﾁﾄｴﾃﾄﾄ47Rﾄ< LS
ﾚﾄﾄﾄﾄﾄｴ ｳ D3 ｳ ｳ ｳ ｳ 10M ｳ DETECTOR
ｳ ﾃﾄｴﾃﾄﾁﾄｴ<ﾃﾄﾁﾄﾄﾁﾄﾄﾄﾁﾄﾄﾄﾄﾙ ﾀﾄﾄﾄﾄ(ﾄﾄﾄﾄﾄﾄﾂﾄﾄﾄﾄﾄﾄﾄﾄﾄﾂﾄﾄﾄﾄﾄﾄ> PTT
10M ｳ u1 DETECTOR ｳ ｳ ｳ
ｳ ｳ/ 4K7 ｳ/ BC107 _ｳ_
ﾄﾄｴﾃﾄﾁﾄｴ BC109 ﾃﾄﾄﾄﾄｴ NPN /_\ back
u1 FB ｳ\e 4K7 ｳ\e D6 ｳ EMF
MIC ｳ ｳ ｳ ｳ
ﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾁﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾁﾄﾄﾄﾄﾄﾄﾁﾄﾄﾄﾄﾄﾄﾄﾄﾄﾁﾄﾄﾄﾄﾄﾄ< GND
MIC AMP PTT DRIVER
All diodes are 1N4148 or Germanium point contact type.
HOW IT WORKS
The BC109 Mic high gain amp is RF protected by the Ferrite Bead on the base
lead. Its' low level output is voltage doubled with Germanium diodes D2 & D3
into double time constants Caps to give fast attach & slow decay time
responces. The rectified DC is referenced from the +ve rail less the voltage
drop of Silicon diode D1 together with the germanium detector diodes, this
makes the Mic Audio detector very sensitive! The voltage is put across the 220K
VOX gain pot, & the hang time determined by the 220K decay variable control
that discharges the capacitors.
The gain controlled sample of the DC switches on the PNP which turns on the NPN
PTT drive transistor, that is protected from rig relay back EMF by D6. The 10M
from the PNP base to NPN collector, gives positive feedback hysteresis if
needed (SCHMITT) for snap on-off action.
High level LS audio is also voltage doubled with Silicon diodes D4 & 5 to give
DC that feeds the ANTI VOX control, this DC is used on the emitter of the PNP
to stop the PTT operating from loud RX LS audio that may be heard by the mic.
See my Tech Bul "Rig DC Power & RF Hazards"
Why Don't U send an interesting bul?
73 De John, G8MNY @ GB7CIP
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