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From: hajo.brandt.dj1zb@t-online.de
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To:  <rsgb_lf_group@blacksheep.org>
Date: 22 Sep 2010 21:30 GMT
Message-ID: <1OyWth-1z20gq0@fwd07.t-online.de>
Subject: Re: LF: PA0RDT miniwhip in TX?
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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
=20

"Marco IK1ODO" <ik1odo@spin-it.com> schrieb:
> Hello Gerhard,
>=20
> the 100n capacitor will do nothing, it is in series with the input=20
> pad capacitance (a few pF).
> The diodes will clamp at 0.6 V, that is too low (every static "crack"=20
> will send the diodes in conduction) and limits the dynamic range.
> More, they will add capacity (2 pF each?) at the very critical point=20
> of the amplifier input, decreasing the gain.
> I think I will leave the gate alone, as in the original design.
>=20
> Possibly the idea of a small reed relay to be closed in TX may be=20
> better; those have very low C. But I will do that only after the=20
> ninth burnt J310 - they are so cheap from Roelof :-) (just jocking,=20
> of course, I could not resist)
>=20
> 73 - Marco IK1ODO
>=20
>=20
>=20