My preffered solution would be protective diode to keep base at -0,7 V
maximum.
Makes me sleep better when RF present! I'd hate to strech Zener avalanche
much.
73 de Mario, S56A, N1YU
----- Original Message -----
From: "Bill Turner" <dezrat1242@ispwest.com>
To: "Marijan Miletic, S56A" <s56a@bit.si>
Cc: <rtty@contesting.com>
Sent: Friday, December 31, 2004 2:37 AM
Subject: Re: [RTTY] QUESTION & ANSWER
> On Fri, 31 Dec 2004 00:25:22 +0100, Marijan Miletic, S56A wrote:
>
> >It would be healthy to add another 1 kOhm resistor from base to ground in
> >order to conform with -5 V max inverse voltage from PC COM port.
> >Shunt capacitor of 10 nF is also highly recommended at collector output
in
> >order to prevent RF feedback to base and subsequent blocking.
> >This solves 99% of hamradio problems but it is missing in 99% of
schematics!
> ___________________________________________________________
>
> I agree about the capacitor from collector to ground, but the resistor
> from base to ground isn't really necessary. Many hams don't know it,
> but the base-emitter junction of a typical small transistor acts like
> a five to seven volt zener diode when reverse biased, and it will
> simply conduct a tiny amount of reverse current, limited by the 1k
> resistor. Completely harmless.
>
> I have used the identical circuit built into a DB-9 connector for over
> ten years and it's still going strong, 45,000 QSOs later. :-)
>
> --
> Bill, W6WRT
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