[nos-bbs] PTT protection circuit (finally found it) !

[M Langelaar]

Reading the fine print and doing a bit more research ... typical of my
over enthusiasm perhaps, getting tired of it :(

G8AMG specifically mentions TTL level (0 to 5) and NOT the rs232 levels
that I see on my actual computer port (-6 to +12). This circuit still works,
but I am observing it does not the odd time, perhaps sitting on high for
too long (again, not sure if that's always the case), so I finally took out
the volt meter, and at one point the electrolytic has a reverse voltage
on it (which is not good). Meaning my serial port is RS232 (not TTL).

Beware, the circuit is for TTL level - meaning I need to 'convert RS232 to
TTL' type of thing. I'm very sorry for missing that. Getting back to the odd
thing above, a few times the MOSFET refused to pinch off, could just be
a bad capacitor (grabbed from my junk box), not so sure about that.

Anyways, so I'm not quite out of the water on this design, so my apologies
for getting over enthusiastic. I have decent experience with 
electronics, but
my lack of ability to zone into details when needed is not helpful at all.

Maiko / VE4KLM

On 28/01/2022 8:47 p.m., M Langelaar wrote:

> Happy Friday !
>
> I found a very interesting circuit recently, see further below, an 
> article from
> the year 2002, by Roger Barker (SK), talking about circuit from G8AMG.
>
> NOTE : Use at your own risk. I'm not to blame if you blow up your
>             Rig or Transmitter or Antenna System or whatever ...