"Uncle Peter" wrote in message
...
Dave

A Zener acts like a regular diode in one direction, the
Zener is actually a back biased diode that is run into
it's reverse breakdown point (over simplification). You
could use two Zeners in SERIES to clamp an AC voltage.

I think you should start by giving us some parameters.

1. What kind of receiver are you trying to protect; tube
or solid state?

2. Are there any transmitters nearby (ham or CB)?

3. What kind of antenna (long wire, dipole, etc.)

4. Urban or rural environment, nearby AM broadcast
facilities?

Some other things that you might consider would be
adding a sacrificial fuse in line with the protection, say
when the diodes or gas arrestor clamp you could have
a 47 pilot lamp wired in series with the antenna to limit
the current to diodes.

Pete



Hello Pete,

Thank you for your reply, and for the questions. My RF amplifier (HF) is
solid state, and there is a Ham transmitter two doors down on the same side
or the street I live on (urban environment) but no other AM transmitters
*that I know of* in the vicinity. I live on the industrial side of town
however, and imagine that there probably are some for the various trucking
companies etc. which operate within five or ten miles of my home. The
antenna is a longwire, consisting of approximately 100' of four (insulated)
parallel strands of #24 AWG copper wire running along the ridge-vent of my
house. This feeds into another 60' or so of RG-59 coax to shield against
noise from the A/C compressor on that side of the house. It is grounded
both where it comes off the roof and again where it comes in my window with
10' copper-clad steel grounding rods driven into the moist earth. The RF
amplifier is a home-brew version of the MFJ 1020-A, using an air-gap (I hope
I have this right) transmitter style variable capacitor for tuning, and has
a 630V .1uF capacitor salvaged from the guts of an old TV connecting the
center conductor of the coax to this tuning capacitor. I do not know the
internal composition of this .1uF capacitor, but assume (hate that word) it
is compatible with RF applications since it came out of the RF circuitry of
a TV. I used to have a .22uF 50V polyethylene capacitor in its place, but
that got blown, alerting me to the possibility of static charges coming down
the feedline. Since my antenna is a longwire on the roof of my house, and
it does routinely get windy, I imagine static will be an ongoing threat.

You mention that two Zener diodes in series could be used to clamp an AC
voltage. Could they be used to defend against static? I have two 5.6V
Zeners rated at 5W, and would love to employ them in this endeavor. I also
have a couple of standard diodes rated at 600 volts PIV and 1 amp. I was
thinking of using these, reversed and in parallel with the neon bulb, to
take any voltage over the .6 volt threshold of silicon PN devices to ground.
Do you think they would do this if I put them between the center conductor
of the coax and ground? I am thinking that the "normal" signal level coming
from the antenna would probably be something on the order of a couple
hundred microvolts, and would therefore not be enough to drive the diodes
into conduction. Does this sound reasonable, or am I way off base here?

Thank you for your time and interest. I really have no idea what I am doing
here, but I am trying to figure it out and plan as best I can.

Best regards,

Dave