Dear all
for input protection I am using one 1N4148 from gate to ground and
another one from gate to the positive rail, both diodes in reverse
polarity, independantly whether the device is a FET or an operational
amplifier.
The capacity added by the protection diodes can be accepted if the
aerial capacity is increased a bit. There will be a capacitive divider
at the input anyway.
No problems with this solution so far.
73 Ha-Jo, DJ1ZB
"Marco IK1ODO" <[email protected]> schrieb:
> Hello Gerhard,
>
> the 100n capacitor will do nothing, it is in series with the input
> pad capacitance (a few pF).
> The diodes will clamp at 0.6 V, that is too low (every static "crack"
> will send the diodes in conduction) and limits the dynamic range.
> More, they will add capacity (2 pF each?) at the very critical point
> of the amplifier input, decreasing the gain.
> I think I will leave the gate alone, as in the original design.
>
> Possibly the idea of a small reed relay to be closed in TX may be
> better; those have very low C. But I will do that only after the
> ninth burnt J310 - they are so cheap from Roelof :-) (just jocking,
> of course, I could not resist)
>
> 73 - Marco IK1ODO
>
>
>
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