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G8MNY > TECH 12.10.25 16:45l 66 Lines 3357 Bytes #9 (0) @ WW
BID : 42630_GB7CIP
Subj: Comms Noise Squelch IC
Path: JH4XSY<N3HYM<VE3CGR<IR0AAB<I0OJJ<N6RME<CX2SA<ED1ZAC<GB7CIP
Sent: 251012/0740Z @:GB7CIP.#32.GBR.EURO #:42630 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To : TECH@WW
By G8MNY (Correction Nov 09)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
This is an old circuit that was published in Sept 1982 Electronic's World
By LJ Forrest.
I have used a HiFi version on the HiFi sound channel on 23cms ATV repeater
GB3HV in an attempt to remove radar zips, as well as providing a squelch.
It uses an KB4432, KB4436 or TDA1001(A) IC, that has 5 NPN emitter follower
buffers, an FET switch, a Schmitt Trigger, a monostable & a regulator. So it is
possible to make up the circuit with discreet components if you can't source
this old IC.
+ve ﾄﾄ100Rﾄﾂﾄﾄﾄﾄﾂﾄﾄﾄﾄﾄﾂﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾂﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾂﾄﾄﾄﾄﾄﾂﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄｿ
ｳ +=== 150R 47n ===220n 1K8 ｳ ｳ
ｳ 47uﾃﾄﾄﾄﾄﾄ)ﾄﾄﾄﾄﾄﾄﾄﾄｴﾃﾄｿ ﾃﾄﾄﾄﾄﾄ5K6ﾄﾄﾄｴ ｳ ｳ/e
ﾚﾄﾄﾄﾄﾄ)ﾄﾄﾄﾄ)ﾄﾄﾄﾄﾄ)ﾄﾄﾄﾄﾄｿ ｳ ﾃﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄ)ﾄﾄﾄﾄﾄ)ﾄﾄﾄﾄ6K8ﾄﾄﾄｴT1
ｳ ｳ ﾚﾄﾄｴ ﾃﾄﾄｴﾃﾄｴ ｳ ｳ ｳ ｳ ｳ\
ｳ ｳ ﾁ ｳ ｳ1n 4K7 3K3 ｳ ﾚﾄﾄﾄﾄﾄ)ﾄﾄﾄﾄﾄ)ﾄﾄﾄﾄﾂﾄﾄｿ ｳ
ｳ ｳ 16ﾃﾄ68Kﾄｴ15 ｳ14 ｳ13 ｳ12 ｳ11 ｳ10 ｳ9 ｳ 330R ｳ
ｳ ｳ ﾚﾄﾅﾄﾄﾄﾄﾄﾅﾄﾄﾄﾄﾄﾅﾄﾄﾄﾄﾄﾅﾄﾄﾄﾄﾄﾅﾄﾄﾄﾄﾄﾅﾄﾄﾄﾄﾄﾅﾄﾄﾄﾄﾄﾅﾄｿ 6K8 ｳ2n2 ｳ
ｳ ｳ ｳ-ve ｳ ｳ ﾚﾄﾄﾄﾁﾄﾄﾄﾄﾄﾁﾄﾄｿ ﾚﾁﾄﾄﾄﾄﾄﾁｿ reg ｳ ｳ === ｳ
ｳ ｳ ｳ ﾀﾄｴ>ﾄﾄﾁﾄｴ shcmit agc ﾃ>ｴ mono ｳ ｳ ﾁﾄﾄﾁﾄ ｳ
ｳ 33K ｳ ﾀﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾙ ﾀﾄﾄﾄﾂﾄﾄﾄﾙ ｳ 6k8
ｳ ｳ ｳ fetﾚﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾙ ｳ ｳ
Rx ｳ ｳ ｳ ﾚﾄｴ>ﾄﾄｿ ﾚﾄｴ>ﾄﾄﾂﾄo/'oﾂﾄﾄｴ>ﾄｿ ﾚﾄﾄｴ>ﾄｿ ｳ ｳ
Inputｳ ｳ ﾀﾄﾅﾄﾄﾄﾄﾄﾅﾄﾄﾄﾄﾄﾅﾄﾄﾄﾄﾄﾅﾄﾄﾄﾄﾄﾅﾄﾄﾄﾄﾄﾅﾄﾄﾄﾄﾄﾅﾄﾄﾄﾄﾄﾅﾄﾙ ｳ Output
>ﾄｴﾃﾄ)ﾄ3K3ﾄﾁﾄﾄﾄﾄｴ1 ｳ2 ｳ3 ｳ4 ｳ5 ｳ6 7 8 ｳ +
1u +ｳ ｳ ｳ 6n8=== 1K8 ｳ ﾀﾄ6K8ﾄﾂﾄﾄﾄﾄﾄﾄﾄﾄｴ>ﾃﾄﾄﾄﾄﾄﾄﾄ)ﾄﾄﾂｴﾃﾄ>
ﾃﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄ)ﾄﾄｴﾃﾄｴ ﾀﾄ12Kﾄｴ 1K8 \ｳ ｳ ｳ 1uF
47K ｳ 1n ﾀﾄﾄ12Kﾄﾄﾄﾄﾄﾄﾙ ｳ T2ﾃﾄﾂﾄﾄﾄﾂﾄﾄﾄﾂﾄﾄ6K8ﾄｴ 6K8
Pre === ===6n8 e/ｳ un 6K8+ ｳ10u +ｳ ｳ
Sensｳ n22ｳ ｳ ｳ mute ｳ === 10u=== ｳ
ﾄﾄﾄﾄﾁ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ﾁﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾄﾁﾄﾄﾄﾁﾄﾄﾄﾁﾄﾄﾄﾁﾄﾄﾄﾄﾄﾄﾁﾄﾄﾁﾄﾄﾄ
HOW IT WORKS
The input signal is fed via a RF filter to biased up the emitter follower amp
on Pin 1. Pin 2 output feeds two paths 1/ the audio path, where it goes to a
low pass Butterworth filter Pin 3 & 4 amp, & 2/ the noise path, where it feeds
an adjustable high pass Butterworth filter on Pin 15 & 16 amp. The noise amp
feeds the Schmitt trigger with a level following AGC. With no noise the
monostable is not triggered. The un-triggered monostable operates the FET hold
level switch that lets the audio pass to the storage CR & to the last buffer
amp Pin 5 & 6.
With impulsive noise present, the high frequency content will operate the
Schmitt & triggers the short time mono, which turns off the FET path for a few
mS. During this time, the mean level stored on CR is used to hold the AF level
during the break into the last buffer.
With constant noise the Schmitt trigger output also drives PNP T1 that after a
fraction of a second charges up the squelch time constants to operate NPN T2
that mutes the output.
See my Tech bul "Simple Carrier Squelch"
Why don't U sent an interesting Bul?
73 De John, G8MNY @ GB7CIP
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