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? on neon light as static discharge device
"Arv" wrote in message ups.com... 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 _._ Wow. Thanks for the info on how the neon bulb works. I had no idea it became a short once the gas was ionized, but now that makes sense. I need to check out the pointed-metal device you describe. Sounds good, but I am really trying to build the static protection into my RF amplifier so that it goes wherever the amplifer goes. Afraid of someone scruffing their feet on the carpet and touching the built-in extendable antenna. Thanks, Arv, for the informative post. Much food for thought... Dave |
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