On 16 Mar, 19:40, Chris Jones wrote:
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

The so-called 125 volt neon bulb is probably a 50 volt neon bulb with
a 47K to 150K resistor in series. Without the resistor it would draw
too much current from the 125 volt mains and either trip a circuit
breaker or destroy the NE-2 bulb, probably both.

An NE-2 bulb has a breakdown potential of approximately 50 volts
(slightly more or less depending on external light conditions). If
your transmitter never puts more than 50 volts on the feed line you
could conceivably use this for a impulse suppression device, but bear
in mind that it will not protect your receiver from voltages of less
than 50 volts. Once the gas in a neon bulb reaches the breakdown
point (50 volts in an NE-2) it becomes a short circuit until the
voltage drops below the breakdown point.

If you are plagued by static build up on your antenna, and if your
feed line normally operates at a low impedance (i.e. 50 ohms) you can
use a 10K ohm 2-watt non-inductive resistor to bleed off the static
build up. Do not use a wire wound resistor because it's inductance
may have a negative impact on feed line SWR. If you want to prevent
close-in lightning strikes from causing impulse voltage of over 50
volts you can use that NE-2, but there are better devices like the
telephone protector that a previous post recommended. Many persons
use a simple impulse protector that is homemade from two pointed
sections of metal with one tied to your feed line and the other
connected to a good earth ground. This method is documented in most
ham radio antenna handbooks.

Arv
_._