"Chris Jones" wrote in message
...
Dave wrote:


"Chris Jones" wrote in message
...
Dave wrote:

I saw somewhere that you could use an NE-2 bulb between the antenna
"hot" lead and ground as a static discharge device for a receiver, but
can't find
an NE-2 and don't know anything about neon bulbs. Anybody know if a
standard neon bulb rated at 125 VAC could be used in this manner? Or
how I
could test it? I'm thinking about charging up a 50V electrolytic
capacitor
and hitting the bulb with that, to see if it discharges the cap. I
have
a .22uF 630V mylar cap between the antenna and the input to the tuner
because the 35V disc I had there got blown, so I know that static can
be
a
problem with my setup even though it is grounded at two points.
Would welcome any ideas anyone has on how to make this work...

Thanks,

Dave

Your "standard neon bulb rated at 125 VAC" probably contains a series
resistor of maybe 100kOhms, and so will be not much use for protecting
anything, because any current would develop too much voltage across the
series resistor. If you open it up and remove the resistor then it will
be
able to shunt larger currents, though it still may not be ideal for
protecting receivers. (The main advantage of the neon as a protection
device is very low capacitance which could be important on the higher
frequency bands, but another advantage would be that it would introduce
practically no intermodulation even in very strong signal conditions,
but
the breakdown voltage is probably so high that it may not protect
solid -
state receivers very well, as someone else already mentioned. You can
buy a ceramic cased gas discharge surge arrestor, they are popular for
telephone circuits. e.g.:
http://www.epcos.com/inf/100/ds/ec350xx0810.pdf
)

You can probably make the bare neon bulb flicker by charging up
something
with static electricity (e.g. rub a balloon on your head or on a jumper)
and then hold this near the bulb so you can hear crackling.

Chris

Hey Chris,

Thanks for the input. I am wondering why a neon bulb would include a
100K
resistor... To maybe lessen the current being driven through the bulb?
I'm
going to have to check that out. Still, I am thinking that a couple of
back-to-back diodes each with a 100K resistor in series would probably do
what I want. Going to try my hand at building a test-bed and give it a
shot. Will check out the gas discdharge surge arrestor though. Sounds
much simpler, and likely more reliable.

Appreciate your feeback.

Dave

I think that the diodes with resistors in series will probably not be
ideal.


I was intendending to connect the diodes in parallel, such as you describe
below. Sorry for the lack of clarity...


If you want to just discharge small steady currents of static electricity
being picked up by your antenna then all you need is a 100k (or 10k)
resistor from the antenna to ground.

If you want to protect against voltage spikes (e.g. caused by distant
lightning), (practically nothing will stop direct lightning) then your
diodes, connected in parallel, and one pointing in each direction, will
offer some protection, but in that case you must leave out the series
resistors because the series resistors will stop the diodes from
performing
any useful function.

Why would the resistors disable the diodes? I expected they would merely
limit the current through the diodes...

If you are likely to experience strong radio signals
that could produce more than 0.2V on your antenna (and I would guess that
the answer is likely to be yes), then maybe the diodes will introduce
intermodulation (a form of interference) into your signal. In this case,
a
number of diodes in series, in each direction, will allow larger RF
signals
to pass without excessive distortion.

\|/
| Antenna
|
*-----\/\/\/\------. 100k resistor
| |
*--||--||--||---* 3x diodes, one direction
| |
*---||--||--||--* 3x diodes, other direction
| |
'--||--To Rx ___ Earth
Cap _
.

For very high frequencies, small diodes such as 1N4148 may be needed,
though
for lower frequencies you may be able to get away with using larger, more
robust diodes. At higher frequencies, big diodes may have too much
capacitance.

I am working in the HF region, 2-30 MHz.


This won't give all that much protection against powerful surges, so if
your
radio is especially valuable then a commercial protection device might be
a
good idea, and in any case unplugging the antenna when not in use would be
sensible.

Oh yes, I do unplug it when not in use. Definetly.


Instead of the above circuit using the diodes in parallel, you could also
try using a pair of zener diodes in series, one pointing in each
direction.


I was thinking about Zener diodes, and trying to figure how they might be
applied. My only hesitation there is the power dissipation capabilities of
Zeners, compared to standard diodes.

Chris


Thank you very much for the input. I appreciate the chance to bounce ideas
off of other people and hear their responses.

Dave

Dave wrote:


"Chris Jones" wrote in message
...
Dave wrote:


"Chris Jones" wrote in message
...
Dave wrote:

I saw somewhere that you could use an NE-2 bulb between the antenna
"hot" lead and ground as a static discharge device for a receiver, but
can't find
an NE-2 and don't know anything about neon bulbs. Anybody know if a
standard neon bulb rated at 125 VAC could be used in this manner? Or
how I
could test it? I'm thinking about charging up a 50V electrolytic
capacitor
and hitting the bulb with that, to see if it discharges the cap. I
have
a .22uF 630V mylar cap between the antenna and the input to the tuner
because the 35V disc I had there got blown, so I know that static can
be
a
problem with my setup even though it is grounded at two points.
Would welcome any ideas anyone has on how to make this work...

Thanks,

Dave

Your "standard neon bulb rated at 125 VAC" probably contains a series
resistor of maybe 100kOhms, and so will be not much use for protecting
anything, because any current would develop too much voltage across the
series resistor. If you open it up and remove the resistor then it
will be
able to shunt larger currents, though it still may not be ideal for
protecting receivers. (The main advantage of the neon as a protection
device is very low capacitance which could be important on the higher
frequency bands, but another advantage would be that it would introduce
practically no intermodulation even in very strong signal conditions,
but
the breakdown voltage is probably so high that it may not protect
solid -
state receivers very well, as someone else already mentioned. You can
buy a ceramic cased gas discharge surge arrestor, they are popular for
telephone circuits. e.g.:
http://www.epcos.com/inf/100/ds/ec350xx0810.pdf
)

You can probably make the bare neon bulb flicker by charging up
something
with static electricity (e.g. rub a balloon on your head or on a
jumper) and then hold this near the bulb so you can hear crackling.

Chris

Hey Chris,

Thanks for the input. I am wondering why a neon bulb would include a
100K
resistor... To maybe lessen the current being driven through the bulb?
I'm
going to have to check that out. Still, I am thinking that a couple of
back-to-back diodes each with a 100K resistor in series would probably
do
what I want. Going to try my hand at building a test-bed and give it a
shot. Will check out the gas discdharge surge arrestor though. Sounds
much simpler, and likely more reliable.

Appreciate your feeback.

Dave

I think that the diodes with resistors in series will probably not be
ideal.


I was intendending to connect the diodes in parallel, such as you describe
below. Sorry for the lack of clarity...


If you want to just discharge small steady currents of static electricity
being picked up by your antenna then all you need is a 100k (or 10k)
resistor from the antenna to ground.

If you want to protect against voltage spikes (e.g. caused by distant
lightning), (practically nothing will stop direct lightning) then your
diodes, connected in parallel, and one pointing in each direction, will
offer some protection, but in that case you must leave out the series
resistors because the series resistors will stop the diodes from
performing
any useful function.

Why would the resistors disable the diodes? I expected they would merely
limit the current through the diodes...

Yes it will limit the current through the diodes. That is the problem: the
current that is not able to flow through the diodes will flow through your
RX instead. It is better to remove the resistors in series with the
diodes, since the current will do less harm (or less expensive harm) if it
flows in the diodes instead of your RX.


If you are likely to experience strong radio signals
that could produce more than 0.2V on your antenna (and I would guess that
the answer is likely to be yes), then maybe the diodes will introduce
intermodulation (a form of interference) into your signal. In this case,
a
number of diodes in series, in each direction, will allow larger RF
signals
to pass without excessive distortion.

\|/
| Antenna
|
*-----\/\/\/\------. 100k resistor
| |
*--||--||--||---* 3x diodes, one direction
| |
*---||--||--||--* 3x diodes, other direction
| |
'--||--To Rx ___ Earth
Cap _
.

For very high frequencies, small diodes such as 1N4148 may be needed,
though
for lower frequencies you may be able to get away with using larger, more
robust diodes. At higher frequencies, big diodes may have too much
capacitance.

I am working in the HF region, 2-30 MHz.


This won't give all that much protection against powerful surges, so if
your
radio is especially valuable then a commercial protection device might be
a
good idea, and in any case unplugging the antenna when not in use would
be sensible.

Oh yes, I do unplug it when not in use. Definetly.


Instead of the above circuit using the diodes in parallel, you could also
try using a pair of zener diodes in series, one pointing in each
direction.


I was thinking about Zener diodes, and trying to figure how they might be
applied.

\|/
| Antenna
|
*-----\/\/\/\------. 100k resistor
| |
| / / |
*--||-------||---* Two Zeners, in series, opposite directions
| / / |
| |
'--||--To Rx ___ Earth
Cap _

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

"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