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. Far better to make
sure your aerial has a DIRECT path to earth - a low impedence one at
that. Best way to avoid static damage? Disconnect the hardware from the
wire when you think there's static about. Oh - and avoid using
headphones....


Good luck.
K



mike wrote in
:

Hey group,

I have a portable radio with no external ground.

Recently I built a PI network antenna tuner in a metal box and
included an output for earth ground. So the outer sheild of my coax
inputs as well as outputs and the variable capacitor frames are on
this ground to earth. The random wire input goes strait to the tuning
capacitor thus needs some kind of static drain off.

I have heard using a neon bulb and a 2 watt 2.2k ohm resistor in
between the inputs and ground would discharge static buildup and give
me some warning of build up conditions.

I am also concerned about limiting the voltage to the receiver front
end to prevent damage. I have heard installing back to back high speed
diodes between the imputs and ground would acheive this.

I understand everything but the diodes. What does back to back mean. I
recall diodes are one way, but which way goes where? Should I look for
a certain type or rating of diode?


Thanks for your help,

Mike