In article , Dick Carroll
writes:

Kieren wrote:

Back to back: Take your two diodes and install them in parallel, but
with one 'pointing' in the opposite direction. The idea is that, because
each diode will conduct when the voltage rises above it's threashold, it
doesn't matter if the spike is positive or negative. A radio signal is
highly unlikely to be powerful enough to force either diode to conduct
(and if it did, they'll protect the RX front end).

I don't think they'd help much however! You only have to think about the
kind of potential in a static build-up to decide that you do not want to
rely on a pair of diodes to keep everything calm.

Once the static voltage builds to .7 volt one or the other diode will
conduct and "bleed" it off. Of course that assumes that we're not
talking of lightning-level static charge. In that case all bets are off.

Not quite right.

Semiconductor diodes will BEGIN conducting at lower voltages. Do a
V-I curve of forward conduction polarity to see that. That's a simple
test with a low voltage supply, a pot, a resistor, and a low-range
voltmeter.

Many HF and MF installations use an RF choke of sufficient impedance
placed across the antenna terminals to provide a discharge path for all
static voltages to be immediately shunted to ground without disturbing
the received radio signal in any way. No static ever builds up on the
antenna. All it takes is a small RF choke of sufficient impedance to be
transparent at the frequency of interest.

Not quite right. A reasonably-high value inductance in parallel with any
antenna is "transparent" at DC (limited to DC resistance) but is a VERY
high value of reactance at RF. X_L = 2 pi L. A 2.5 mHy RFC will have
a reactance of 15.7 KOhms at 1 MHz. Even with a long-wire whose
maximum impedance magnitude might reach 5 KOhms, the effect of
paralleling such an RFC is negligible. [in parallel it would be 3.8 KOhms]
At higher frequencies the inductive reactance is proportionally higher.

What MIGHT happen, depending on the particular inductor, is that the
inductor's self-resonance due to distributed capacity would defeat the
high-frequency reactance. Above self-resonance the RFC would appear
as a capacitor.

Len Anderson
retired (from regular hours) electronic engineer person