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? on neon light as static discharge device
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 _ |
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