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Static discharge protection questions
Hey group,
I have a portable radio with no external ground. Recently I built a PI network antenna tuner in a metal box and included an output for earth ground. So the outer sheild of my coax inputs as well as outputs and the variable capacitor frames are on this ground to earth. The random wire input goes strait to the tuning capacitor thus needs some kind of static drain off. I have heard using a neon bulb and a 2 watt 2.2k ohm resistor in between the inputs and ground would discharge static buildup and give me some warning of build up conditions. I am also concerned about limiting the voltage to the receiver front end to prevent damage. I have heard installing back to back high speed diodes between the imputs and ground would acheive this. I understand everything but the diodes. What does back to back mean. I recall diodes are one way, but which way goes where? Should I look for a certain type or rating of diode? Thanks for your help, Mike |
Back to back: Take your two diodes and install them in parallel, but
with one 'pointing' in the opposite direction. The idea is that, because each diode will conduct when the voltage rises above it's threashold, it doesn't matter if the spike is positive or negative. A radio signal is highly unlikely to be powerful enough to force either diode to conduct (and if it did, they'll protect the RX front end). I don't think they'd help much however! You only have to think about the kind of potential in a static build-up to decide that you do not want to rely on a pair of diodes to keep everything calm. Far better to make sure your aerial has a DIRECT path to earth - a low impedence one at that. Best way to avoid static damage? Disconnect the hardware from the wire when you think there's static about. Oh - and avoid using headphones.... Good luck. K mike wrote in : Hey group, I have a portable radio with no external ground. Recently I built a PI network antenna tuner in a metal box and included an output for earth ground. So the outer sheild of my coax inputs as well as outputs and the variable capacitor frames are on this ground to earth. The random wire input goes strait to the tuning capacitor thus needs some kind of static drain off. I have heard using a neon bulb and a 2 watt 2.2k ohm resistor in between the inputs and ground would discharge static buildup and give me some warning of build up conditions. I am also concerned about limiting the voltage to the receiver front end to prevent damage. I have heard installing back to back high speed diodes between the imputs and ground would acheive this. I understand everything but the diodes. What does back to back mean. I recall diodes are one way, but which way goes where? Should I look for a certain type or rating of diode? Thanks for your help, Mike |
Back to back: Take your two diodes and install them in parallel, but
with one 'pointing' in the opposite direction. The idea is that, because each diode will conduct when the voltage rises above it's threashold, it doesn't matter if the spike is positive or negative. A radio signal is highly unlikely to be powerful enough to force either diode to conduct (and if it did, they'll protect the RX front end). I don't think they'd help much however! You only have to think about the kind of potential in a static build-up to decide that you do not want to rely on a pair of diodes to keep everything calm. Far better to make sure your aerial has a DIRECT path to earth - a low impedence one at that. Best way to avoid static damage? Disconnect the hardware from the wire when you think there's static about. Oh - and avoid using headphones.... Good luck. K mike wrote in : Hey group, I have a portable radio with no external ground. Recently I built a PI network antenna tuner in a metal box and included an output for earth ground. So the outer sheild of my coax inputs as well as outputs and the variable capacitor frames are on this ground to earth. The random wire input goes strait to the tuning capacitor thus needs some kind of static drain off. I have heard using a neon bulb and a 2 watt 2.2k ohm resistor in between the inputs and ground would discharge static buildup and give me some warning of build up conditions. I am also concerned about limiting the voltage to the receiver front end to prevent damage. I have heard installing back to back high speed diodes between the imputs and ground would acheive this. I understand everything but the diodes. What does back to back mean. I recall diodes are one way, but which way goes where? Should I look for a certain type or rating of diode? Thanks for your help, Mike |
On 21 Sep 2003 21:30:28 GMT, Kieren wrote:
Back to back: Take your two diodes and install them in parallel, but with one 'pointing' in the opposite direction. The idea is that, because each diode will conduct when the voltage rises above it's threashold, it doesn't matter if the spike is positive or negative. A radio signal is highly unlikely to be powerful enough to force either diode to conduct (and if it did, they'll protect the RX front end). I don't think they'd help much however! You only have to think about the kind of potential in a static build-up to decide that you do not want to rely on a pair of diodes to keep everything calm. Far better to make sure your aerial has a DIRECT path to earth - a low impedence one at that. Best way to avoid static damage? Disconnect the hardware from the wire when you think there's static about. Oh - and avoid using headphones.... Good luck. K OK I get it now. As for an earth ground......I found a nice fat copper braided wire coming off the metal roof lightning protectors (this is an old farmhouse) down the side of the house going deep into the ground. I suspect if I solder a nice fat 12 guage wire to my random wire where it meets my coax it would suffice in this regard. Additionaly I will run another wire to this ground from my tuner. thanks, mike |
On 21 Sep 2003 21:30:28 GMT, Kieren wrote:
Back to back: Take your two diodes and install them in parallel, but with one 'pointing' in the opposite direction. The idea is that, because each diode will conduct when the voltage rises above it's threashold, it doesn't matter if the spike is positive or negative. A radio signal is highly unlikely to be powerful enough to force either diode to conduct (and if it did, they'll protect the RX front end). I don't think they'd help much however! You only have to think about the kind of potential in a static build-up to decide that you do not want to rely on a pair of diodes to keep everything calm. Far better to make sure your aerial has a DIRECT path to earth - a low impedence one at that. Best way to avoid static damage? Disconnect the hardware from the wire when you think there's static about. Oh - and avoid using headphones.... Good luck. K OK I get it now. As for an earth ground......I found a nice fat copper braided wire coming off the metal roof lightning protectors (this is an old farmhouse) down the side of the house going deep into the ground. I suspect if I solder a nice fat 12 guage wire to my random wire where it meets my coax it would suffice in this regard. Additionaly I will run another wire to this ground from my tuner. thanks, mike |
In article , mike
writes: Hey group, I have a portable radio with no external ground. Recently I built a PI network antenna tuner in a metal box and included an output for earth ground. So the outer sheild of my coax inputs as well as outputs and the variable capacitor frames are on this ground to earth. The random wire input goes strait to the tuning capacitor thus needs some kind of static drain off. I have heard using a neon bulb and a 2 watt 2.2k ohm resistor in between the inputs and ground would discharge static buildup and give me some warning of build up conditions. A small neon bulb was used in thousands of ARC-5 Command Set receivers in WW2 for static bleed-off. Similar to an old NE-2 bulb. No need to use a resistor. The neon will conduct somewhere around 70 Volts and shunt any static pickup to ground...then goes into non- conducting state until the next static potential build-up. I am also concerned about limiting the voltage to the receiver front end to prevent damage. I have heard installing back to back high speed diodes between the imputs and ground would acheive this. I understand everything but the diodes. What does back to back mean. I recall diodes are one way, but which way goes where? Should I look for a certain type or rating of diode? You can use practically anything modern in the way of diodes there but the high-speed types such as 1N914 and 1N4148 are very cheap and available many places. Varistors could be used (GE "movisters") or even 1N4000 series rectifier diodes. Diodes have a 0.6 to 0.7 VDC forward conduction voltage if silicon. Put them side by side with the anode of one to the cathode of the other at each end. That will limit voltage input to about 1.4 V peak-to- peak. You could put a small series resistor, say 22 Ohms or so, between antenna input and the diodes to limit peak diode current on conduction. Your option...since the series resistor will drop the RF input level slightly. You could also use a high-inductance RF "choke" in place of diodes and neon bulb. 1 to 5 mHy would work at HF bands. That forms a constant low-resistance DC path from antenna to ground and keeps static accumulation bled off immediately. Len Anderson retired (from regular hours) electronic engineer person |
In article , mike
writes: Hey group, I have a portable radio with no external ground. Recently I built a PI network antenna tuner in a metal box and included an output for earth ground. So the outer sheild of my coax inputs as well as outputs and the variable capacitor frames are on this ground to earth. The random wire input goes strait to the tuning capacitor thus needs some kind of static drain off. I have heard using a neon bulb and a 2 watt 2.2k ohm resistor in between the inputs and ground would discharge static buildup and give me some warning of build up conditions. A small neon bulb was used in thousands of ARC-5 Command Set receivers in WW2 for static bleed-off. Similar to an old NE-2 bulb. No need to use a resistor. The neon will conduct somewhere around 70 Volts and shunt any static pickup to ground...then goes into non- conducting state until the next static potential build-up. I am also concerned about limiting the voltage to the receiver front end to prevent damage. I have heard installing back to back high speed diodes between the imputs and ground would acheive this. I understand everything but the diodes. What does back to back mean. I recall diodes are one way, but which way goes where? Should I look for a certain type or rating of diode? You can use practically anything modern in the way of diodes there but the high-speed types such as 1N914 and 1N4148 are very cheap and available many places. Varistors could be used (GE "movisters") or even 1N4000 series rectifier diodes. Diodes have a 0.6 to 0.7 VDC forward conduction voltage if silicon. Put them side by side with the anode of one to the cathode of the other at each end. That will limit voltage input to about 1.4 V peak-to- peak. You could put a small series resistor, say 22 Ohms or so, between antenna input and the diodes to limit peak diode current on conduction. Your option...since the series resistor will drop the RF input level slightly. You could also use a high-inductance RF "choke" in place of diodes and neon bulb. 1 to 5 mHy would work at HF bands. That forms a constant low-resistance DC path from antenna to ground and keeps static accumulation bled off immediately. Len Anderson retired (from regular hours) electronic engineer person |
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For Static control, I have a 1 megaohm 1/2 watt resistor to ground from
each side of my antenna. I do this because my balanced antenna tuner does not have a DC path to ground. Notice I said STATIC control, not Lightening arresting. You can use a much lower value. The resistor should be large compared to the impeadence of your anteanna. So if the antenna is 4,000 ohms, even a 400,000 ohm resistor would be 100 times the antenna value. KA9CAR "mike" wrote in message ... Hey group, I have a portable radio with no external ground. Recently I built a PI network antenna tuner in a metal box and included an output for earth ground. So the outer sheild of my coax inputs as well as outputs and the variable capacitor frames are on this ground to earth. The random wire input goes strait to the tuning capacitor thus needs some kind of static drain off. I have heard using a neon bulb and a 2 watt 2.2k ohm resistor in between the inputs and ground would discharge static buildup and give me some warning of build up conditions. I am also concerned about limiting the voltage to the receiver front end to prevent damage. I have heard installing back to back high speed diodes between the imputs and ground would acheive this. I understand everything but the diodes. What does back to back mean. I recall diodes are one way, but which way goes where? Should I look for a certain type or rating of diode? Thanks for your help, Mike |
For Static control, I have a 1 megaohm 1/2 watt resistor to ground from
each side of my antenna. I do this because my balanced antenna tuner does not have a DC path to ground. Notice I said STATIC control, not Lightening arresting. You can use a much lower value. The resistor should be large compared to the impeadence of your anteanna. So if the antenna is 4,000 ohms, even a 400,000 ohm resistor would be 100 times the antenna value. KA9CAR "mike" wrote in message ... Hey group, I have a portable radio with no external ground. Recently I built a PI network antenna tuner in a metal box and included an output for earth ground. So the outer sheild of my coax inputs as well as outputs and the variable capacitor frames are on this ground to earth. The random wire input goes strait to the tuning capacitor thus needs some kind of static drain off. I have heard using a neon bulb and a 2 watt 2.2k ohm resistor in between the inputs and ground would discharge static buildup and give me some warning of build up conditions. I am also concerned about limiting the voltage to the receiver front end to prevent damage. I have heard installing back to back high speed diodes between the imputs and ground would acheive this. I understand everything but the diodes. What does back to back mean. I recall diodes are one way, but which way goes where? Should I look for a certain type or rating of diode? Thanks for your help, Mike |
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In article , mike
writes: A small neon bulb was used in thousands of ARC-5 Command Set receivers in WW2 for static bleed-off. Similar to an old NE-2 bulb. No need to use a resistor. The neon will conduct somewhere around 70 Volts and shunt any static pickup to ground...then goes into non- conducting state until the next static potential build-up. Wow.....70 volts seems a tad high to be protective in my solid state portable. I suspect the older vacuum tube sets were far more static resistant. I've read the limit for my sony portable should be kept below 0.7volts to keep the sensitive front end electronics safe. Allow me to correct a number. The strike voltage of a typical small neon bulb is high but once struck, and a resistor is in series with it, the bulb potential is around 50 VDC. Yes, that IS a high voltage, but I encountered it on a (roughly) 200 foot long-wire that the previous apartment owner had put up to a utility pole prior to 1947. The little bulb in the ARC-5 receiver DID light. On learning some more about neon bulbs (I was 14 at the time), I decided it was not a good thing to have the antenna connected during electrical storm episodes. :-) You can use practically anything modern in the way of diodes there but the high-speed types such as 1N914 and 1N4148 are very cheap and available many places. Varistors could be used (GE "movisters") or even 1N4000 series rectifier diodes. Diodes have a 0.6 to 0.7 VDC forward conduction voltage if silicon. Put them side by side with the anode of one to the cathode of the other at each end. That will limit voltage input to about 1.4 V peak-to- peak. You could put a small series resistor, say 22 Ohms or so, between antenna input and the diodes to limit peak diode current on conduction. Your option...since the series resistor will drop the RF input level slightly. You could also use a high-inductance RF "choke" in place of diodes and neon bulb. 1 to 5 mHy would work at HF bands. That forms a constant low-resistance DC path from antenna to ground and keeps static accumulation bled off immediately. Len Anderson retired (from regular hours) electronic engineer person I've read suggestions for resistors ranging from 2.2 k ohms to 56 k ohms all the way up to 100 k ohms. The most recent information being the lowest value resistors. From the schematics I have seen, the resistors were placed in parralel between the antenna input and ground input. Or in the case of a two wire unbalanced input, between each wire and the case of the tuner which is grounded. Guess I might have to just play resistor values and see what doesnt hurt signal strenth (another suggestion I read). good information though, thanks. - mike A resistor alone will only serve to bleed off any accumulated voltage charge. Relatively slowly. It is NOT any sort of protection from a spike of voltage created by a nearby lightning episode. Those can be anywhere from a few Volts to 300 Volts peak amplitude, polarity either positive or negative depending on what Mother Nature decides at that moment... The "back-to-back" diodes serve as clamps to effect a sudden low- impedance shunt across the input once they conduct past around 0.7 Volts forward (it's not sudden, but gradual, the Z curve has a lot of slope steepness until it really begins to conduct). The reason I mentioned a _series_ resistor between back-to-back diodes and antenna is for three reasons: It limits the peak current in the diodes; it provides a slight voltage-divider effect to reduce peaks (even on conduction) at receiver input; it reduces the rise time of the static peak through a tiny R-C filter effect using the diodes' junction capacitance. In truth, NONE of the above is an guarantee of _protection_ of any receiver input. A slow, gradual charge build-up on an antenna isn't going anywhere as long as _all_ the components involved have insulation breakdown voltages that are high. A resistor by itself will bleed off such slow charge build-up attempts. At around 2.7 KOhms or so, that resistance isn't going to affect high-impedance values much at frequencies well away from resonance of the wire antenna. Since I live in Southern California with a low incidence of electrical storms, I've not concerned myself with electrostatic charges in wire antennas. Being raised in northern Illinois, such were quite common and I've been "bit" by one charge which was probably up around 50 Volts or so on that mentioned long-wire. Lightning storm areas NEED additional protection for outside antennas. Len Anderson retired (from regular hours) electronic engineer person My apologies for the previous posting without content...stupid cat walked across the keyboard...:-( |
In article , mike
writes: A small neon bulb was used in thousands of ARC-5 Command Set receivers in WW2 for static bleed-off. Similar to an old NE-2 bulb. No need to use a resistor. The neon will conduct somewhere around 70 Volts and shunt any static pickup to ground...then goes into non- conducting state until the next static potential build-up. Wow.....70 volts seems a tad high to be protective in my solid state portable. I suspect the older vacuum tube sets were far more static resistant. I've read the limit for my sony portable should be kept below 0.7volts to keep the sensitive front end electronics safe. Allow me to correct a number. The strike voltage of a typical small neon bulb is high but once struck, and a resistor is in series with it, the bulb potential is around 50 VDC. Yes, that IS a high voltage, but I encountered it on a (roughly) 200 foot long-wire that the previous apartment owner had put up to a utility pole prior to 1947. The little bulb in the ARC-5 receiver DID light. On learning some more about neon bulbs (I was 14 at the time), I decided it was not a good thing to have the antenna connected during electrical storm episodes. :-) You can use practically anything modern in the way of diodes there but the high-speed types such as 1N914 and 1N4148 are very cheap and available many places. Varistors could be used (GE "movisters") or even 1N4000 series rectifier diodes. Diodes have a 0.6 to 0.7 VDC forward conduction voltage if silicon. Put them side by side with the anode of one to the cathode of the other at each end. That will limit voltage input to about 1.4 V peak-to- peak. You could put a small series resistor, say 22 Ohms or so, between antenna input and the diodes to limit peak diode current on conduction. Your option...since the series resistor will drop the RF input level slightly. You could also use a high-inductance RF "choke" in place of diodes and neon bulb. 1 to 5 mHy would work at HF bands. That forms a constant low-resistance DC path from antenna to ground and keeps static accumulation bled off immediately. Len Anderson retired (from regular hours) electronic engineer person I've read suggestions for resistors ranging from 2.2 k ohms to 56 k ohms all the way up to 100 k ohms. The most recent information being the lowest value resistors. From the schematics I have seen, the resistors were placed in parralel between the antenna input and ground input. Or in the case of a two wire unbalanced input, between each wire and the case of the tuner which is grounded. Guess I might have to just play resistor values and see what doesnt hurt signal strenth (another suggestion I read). good information though, thanks. - mike A resistor alone will only serve to bleed off any accumulated voltage charge. Relatively slowly. It is NOT any sort of protection from a spike of voltage created by a nearby lightning episode. Those can be anywhere from a few Volts to 300 Volts peak amplitude, polarity either positive or negative depending on what Mother Nature decides at that moment... The "back-to-back" diodes serve as clamps to effect a sudden low- impedance shunt across the input once they conduct past around 0.7 Volts forward (it's not sudden, but gradual, the Z curve has a lot of slope steepness until it really begins to conduct). The reason I mentioned a _series_ resistor between back-to-back diodes and antenna is for three reasons: It limits the peak current in the diodes; it provides a slight voltage-divider effect to reduce peaks (even on conduction) at receiver input; it reduces the rise time of the static peak through a tiny R-C filter effect using the diodes' junction capacitance. In truth, NONE of the above is an guarantee of _protection_ of any receiver input. A slow, gradual charge build-up on an antenna isn't going anywhere as long as _all_ the components involved have insulation breakdown voltages that are high. A resistor by itself will bleed off such slow charge build-up attempts. At around 2.7 KOhms or so, that resistance isn't going to affect high-impedance values much at frequencies well away from resonance of the wire antenna. Since I live in Southern California with a low incidence of electrical storms, I've not concerned myself with electrostatic charges in wire antennas. Being raised in northern Illinois, such were quite common and I've been "bit" by one charge which was probably up around 50 Volts or so on that mentioned long-wire. Lightning storm areas NEED additional protection for outside antennas. Len Anderson retired (from regular hours) electronic engineer person My apologies for the previous posting without content...stupid cat walked across the keyboard...:-( |
Neon bulbs are curious critters. As you say, they have hysteresis -- a
higher strike voltage than sustaining voltage. The company I worked for once used them as low current regulators here and there, as well as for static protection, so they bought or selected them to various specifications for strike and sustaining voltages. Strike voltages varied from 55 minimum to 135 maximum, and sustaining specs went from a minimum of 46 to a maximum of 78. They also exhibited a "dark effect", which I believe was that the strike voltage was dependent on the ambient light level. I recall that a trace radioactive material was added to some -- to reduce the "dark effect", I think, by keeping the gas close to ionization. I imagine the sustaining voltage was controlled by the mixture and pressure of gas. The bulbs were commonly used as pilot lamps, but not when the supply was DC. (This lesson was learned the hard way, judging by company documents and app notes.) Depending on the supply impedance, the pilot bulb could become a relaxation oscillator, interfering with sensitive circuitry. I came in just as their day was ending. Roy Lewallen, W7EL Avery Fineman wrote: Allow me to correct a number. The strike voltage of a typical small neon bulb is high but once struck, and a resistor is in series with it, the bulb potential is around 50 VDC. . . . |
Neon bulbs are curious critters. As you say, they have hysteresis -- a
higher strike voltage than sustaining voltage. The company I worked for once used them as low current regulators here and there, as well as for static protection, so they bought or selected them to various specifications for strike and sustaining voltages. Strike voltages varied from 55 minimum to 135 maximum, and sustaining specs went from a minimum of 46 to a maximum of 78. They also exhibited a "dark effect", which I believe was that the strike voltage was dependent on the ambient light level. I recall that a trace radioactive material was added to some -- to reduce the "dark effect", I think, by keeping the gas close to ionization. I imagine the sustaining voltage was controlled by the mixture and pressure of gas. The bulbs were commonly used as pilot lamps, but not when the supply was DC. (This lesson was learned the hard way, judging by company documents and app notes.) Depending on the supply impedance, the pilot bulb could become a relaxation oscillator, interfering with sensitive circuitry. I came in just as their day was ending. Roy Lewallen, W7EL Avery Fineman wrote: Allow me to correct a number. The strike voltage of a typical small neon bulb is high but once struck, and a resistor is in series with it, the bulb potential is around 50 VDC. . . . |
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On Tue, 23 Sep 2003 12:40:22 GMT, mike wrote:
A side effect I noticed after installing the 1N914 diodes was images scattered across the bands. For example, wwcr on 3200 was also on 2300. Another gentleman posted me link in the antenna group where he found the same thing happening. Might the resistor in series with the diodes reduce this side effect? hmmm... might be my impedance mismatch causing reflections of imcoming signals back and forth along the antenna, thus causing images. probable? mike |
On Tue, 23 Sep 2003 12:40:22 GMT, mike wrote:
A side effect I noticed after installing the 1N914 diodes was images scattered across the bands. For example, wwcr on 3200 was also on 2300. Another gentleman posted me link in the antenna group where he found the same thing happening. Might the resistor in series with the diodes reduce this side effect? hmmm... might be my impedance mismatch causing reflections of imcoming signals back and forth along the antenna, thus causing images. probable? mike |
Roy,
I recall as a kid making a "Decision Maker" project that used two neons to indicate Yes and No. My father thought it was pretty cool, especially when I mentioned that I had noticed it came up on Yes more often. I told him I'd fix it but he seemed insistent that I leave it the way it was. I didn't see it much after that, but suspect it played a part in some gambling game in which he held a decided advantage while being able to claim a totally impartial device. ;-) Rob Roy Lewallen wrote: Neon bulbs are curious critters. As you say, they have hysteresis -- a higher strike voltage than sustaining voltage. The company I worked for once used them as low current regulators here and there, as well as for static protection, so they bought or selected them to various specifications for strike and sustaining voltages. Strike voltages varied from 55 minimum to 135 maximum, and sustaining specs went from a minimum of 46 to a maximum of 78. They also exhibited a "dark effect", which I believe was that the strike voltage was dependent on the ambient light level. I recall that a trace radioactive material was added to some -- to reduce the "dark effect", I think, by keeping the gas close to ionization. I imagine the sustaining voltage was controlled by the mixture and pressure of gas. The bulbs were commonly used as pilot lamps, but not when the supply was DC. (This lesson was learned the hard way, judging by company documents and app notes.) Depending on the supply impedance, the pilot bulb could become a relaxation oscillator, interfering with sensitive circuitry. I came in just as their day was ending. Roy Lewallen, W7EL Avery Fineman wrote: Allow me to correct a number. The strike voltage of a typical small neon bulb is high but once struck, and a resistor is in series with it, the bulb potential is around 50 VDC. . . . |
Roy,
I recall as a kid making a "Decision Maker" project that used two neons to indicate Yes and No. My father thought it was pretty cool, especially when I mentioned that I had noticed it came up on Yes more often. I told him I'd fix it but he seemed insistent that I leave it the way it was. I didn't see it much after that, but suspect it played a part in some gambling game in which he held a decided advantage while being able to claim a totally impartial device. ;-) Rob Roy Lewallen wrote: Neon bulbs are curious critters. As you say, they have hysteresis -- a higher strike voltage than sustaining voltage. The company I worked for once used them as low current regulators here and there, as well as for static protection, so they bought or selected them to various specifications for strike and sustaining voltages. Strike voltages varied from 55 minimum to 135 maximum, and sustaining specs went from a minimum of 46 to a maximum of 78. They also exhibited a "dark effect", which I believe was that the strike voltage was dependent on the ambient light level. I recall that a trace radioactive material was added to some -- to reduce the "dark effect", I think, by keeping the gas close to ionization. I imagine the sustaining voltage was controlled by the mixture and pressure of gas. The bulbs were commonly used as pilot lamps, but not when the supply was DC. (This lesson was learned the hard way, judging by company documents and app notes.) Depending on the supply impedance, the pilot bulb could become a relaxation oscillator, interfering with sensitive circuitry. I came in just as their day was ending. Roy Lewallen, W7EL Avery Fineman wrote: Allow me to correct a number. The strike voltage of a typical small neon bulb is high but once struck, and a resistor is in series with it, the bulb potential is around 50 VDC. . . . |
....[snip]....
I've read suggestions for resistors ranging from 2.2 k ohms to 56 k ohms all the way up to 100 k ohms. The most recent information being the lowest value resistors. From the schematics I have seen, the resistors were placed in parralel between the antenna input and ground input. Or in the case of a two wire unbalanced input, between each wire and the case of the tuner which is grounded. It just depends on how much power you want to "waste" in the paralleled resistor. Think of it this way: IF you had a 50-ohm dipole antenna and you used a 50-ohm resistor across the antenna (and ignoring the effect of a 25-ohm load on your xmtr), half of your power go into the antenna proper and half would be dissipated in the resistor. That's probably too much, so try a 500-ohm resistor: now about 90% of your xmtr power goes into the antenna and 10% into the resistor. One more try: 5K-omn resistor: now about 99% goes into the antenna and 1% is wasted in the resistor. This leads to one of the "rules of thumb" from a beginning EE class oh- so- many years ago: the power loss from paralleling a 100*R-ohm resistor with an R-ohm resistor is essentially negligible. There is another GOOD effect of using any resistor across your feed line: a simple ohm-meter check from inside the shack can tell you if your feed line is intact! --Myron, W0PBV. -- Five boxes preserve our freedoms: soap, ballot, witness, jury, and cartridge PhD EE (retired). "Barbershop" tenor. CDL(PTX). W0PBV. (785) 539-4448 NRA Life Member and Certified Instructor (Home Firearm Safety, Rifle, Pistol) |
....[snip]....
I've read suggestions for resistors ranging from 2.2 k ohms to 56 k ohms all the way up to 100 k ohms. The most recent information being the lowest value resistors. From the schematics I have seen, the resistors were placed in parralel between the antenna input and ground input. Or in the case of a two wire unbalanced input, between each wire and the case of the tuner which is grounded. It just depends on how much power you want to "waste" in the paralleled resistor. Think of it this way: IF you had a 50-ohm dipole antenna and you used a 50-ohm resistor across the antenna (and ignoring the effect of a 25-ohm load on your xmtr), half of your power go into the antenna proper and half would be dissipated in the resistor. That's probably too much, so try a 500-ohm resistor: now about 90% of your xmtr power goes into the antenna and 10% into the resistor. One more try: 5K-omn resistor: now about 99% goes into the antenna and 1% is wasted in the resistor. This leads to one of the "rules of thumb" from a beginning EE class oh- so- many years ago: the power loss from paralleling a 100*R-ohm resistor with an R-ohm resistor is essentially negligible. There is another GOOD effect of using any resistor across your feed line: a simple ohm-meter check from inside the shack can tell you if your feed line is intact! --Myron, W0PBV. -- Five boxes preserve our freedoms: soap, ballot, witness, jury, and cartridge PhD EE (retired). "Barbershop" tenor. CDL(PTX). W0PBV. (785) 539-4448 NRA Life Member and Certified Instructor (Home Firearm Safety, Rifle, Pistol) |
In article , mike
writes: On 23 Sep 2003 05:09:01 GMT, (Avery Fineman) wrote: Silly me, I put them all in parallel.grin. I am a mechanic with some electrical knowledge, but not much electronics. So the resistor should be in series with the diodes to limit current. A side effect I noticed after installing the 1N914 diodes was images scattered across the bands. For example, wwcr on 3200 was also on 2300. Another gentleman posted me link in the antenna group where he found the same thing happening. Might the resistor in series with the diodes reduce this side effect? The effect should not be there with or without diodes, with or without any resistors...unless there is some VERY big RF source out of the receiver's tuning range that is supplying energy to the diodes and thus causing the "mixer" effect. It might be possible if you have some Local Oscillator energy leaking out to the antenna connection, but even that is unlikely given "modern" (in the last couple of decades) receiver design. The diodes should not have any effect on anything but a few millivolts of any signal arriving on your antenna. A non-conducting diode simply shows a junction capacitance to the rest of the world. That's a minor reactive discontinuity to the antenna connection. It might be possible that some unusual circuitry in your receiver presents a DC Voltage at the antenna port. If so, it might cause one of the diodes to conduct. It would be better then to AC-couple the back-to-back diodes to the receiver through a capacitor of 0.001 to 0.01 uFd to eliminate that possibility. You should be able to measure any DC potential at the antenna port with a high impedance multimeter. Len Anderson retired (from regular hours) electronic engineer person |
In article , mike
writes: On 23 Sep 2003 05:09:01 GMT, (Avery Fineman) wrote: Silly me, I put them all in parallel.grin. I am a mechanic with some electrical knowledge, but not much electronics. So the resistor should be in series with the diodes to limit current. A side effect I noticed after installing the 1N914 diodes was images scattered across the bands. For example, wwcr on 3200 was also on 2300. Another gentleman posted me link in the antenna group where he found the same thing happening. Might the resistor in series with the diodes reduce this side effect? The effect should not be there with or without diodes, with or without any resistors...unless there is some VERY big RF source out of the receiver's tuning range that is supplying energy to the diodes and thus causing the "mixer" effect. It might be possible if you have some Local Oscillator energy leaking out to the antenna connection, but even that is unlikely given "modern" (in the last couple of decades) receiver design. The diodes should not have any effect on anything but a few millivolts of any signal arriving on your antenna. A non-conducting diode simply shows a junction capacitance to the rest of the world. That's a minor reactive discontinuity to the antenna connection. It might be possible that some unusual circuitry in your receiver presents a DC Voltage at the antenna port. If so, it might cause one of the diodes to conduct. It would be better then to AC-couple the back-to-back diodes to the receiver through a capacitor of 0.001 to 0.01 uFd to eliminate that possibility. You should be able to measure any DC potential at the antenna port with a high impedance multimeter. Len Anderson retired (from regular hours) electronic engineer person |
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Although 0.7 volts is a good rule of thumb for diode conduction in
moderate impedance environments, it's important to keep in mind that diodes don't abruptly "turn on" at a fixed voltage. They conduct *some* current at *all* forward voltages. It just happens to be an exponential function, so it looks kind of like a sharp knee when viewed on a linear I-V scale. What's important here is how well the diode conducts compared to the circuit it's across. On a lab test bench, that's 25 ohms (50 ohm source and 50 ohm load), but it could be more or less when connected across an antenna. A quick check with a couple of signal generators and a good combiner showed that cross modulation 60 dB below either signal was present when there was about 0.7 volts p-p (peak envelope, that is, at the peaks where both signals are in phase) across a back-to-back pair of 1N914 type diodes with 50 ohms source and load. That's only about 0.35 volts of forward diode voltage. At about 0.8 volts p-p, the cross modulation product was only about 40 dB below either signal. So appreciable cross modulation can occur at least several dB below the 0.7 volt level often considered to be the diode's conduction knee. Paul's caution about multiple signals is important to note. Also remember that under some circumstances (for example, high Z looking into the antenna, and also looking into a tuner or receiver, from where the diodes are mounted), the diode's Z environment can be higher than 25 ohms, resulting in appreciable cross modulation at lower signal levels. Roy Lewallen, W7EL Paul Keinanen wrote: On 24 Sep 2003 22:04:07 GMT, (Avery Fineman) wrote: The effect should not be there with or without diodes, with or without any resistors...unless there is some VERY big RF source out of the receiver's tuning range that is supplying energy to the diodes and thus causing the "mixer" effect. It should also be noted that when several quite strong out of band signals are present at the antenna, say ten signals, each with S9+60 dB, which is 50 mVrms (71 mVpeak) into 50 ohms and -13 dBm. On average, these signals produce a combined signal ten times as large at -3 dB and the rms voltage is about 150 mV. However, from time to time, the vectors for each individual signal add up, so you have to add the _voltages_ for that moment, so the maximum theoretical peak amplitude is 700 mV (10x71 mV), thus, a single silicon diode starts to conduct, causing all kinds of mixing products. Using two (or more) 1N4148 type diodes in series instead of a single diode in the each back to back pair, will prevent any diode conduction as long as the peak voltage is larger than 1,4 V in either direction. The maximum number of diodes in series is determined by the amount of voltage the following stages will tolerate without disintegrating. Since most likely there will be some selectivity between this diode clipper and the first amplifier stage, the amplifier stage will never see voltages as the limiting voltages in normal operation, but the diodes will still cut out some abnormal peaks e.g. induced by lightnings. The diodes should not have any effect on anything but a few millivolts of any signal arriving on your antenna. A non-conducting diode simply shows a junction capacitance to the rest of the world. That's a minor reactive discontinuity to the antenna connection. Putting multiple diodes in series in the back to back combination also reduce the capacitances, since the capacitances in each string are in series. Paul OH3LWR |
In article , Paul Keinanen
writes: On 24 Sep 2003 22:04:07 GMT, (Avery Fineman) wrote: The effect should not be there with or without diodes, with or without any resistors...unless there is some VERY big RF source out of the receiver's tuning range that is supplying energy to the diodes and thus causing the "mixer" effect. It should also be noted that when several quite strong out of band signals are present at the antenna, say ten signals, each with S9+60 dB, which is 50 mVrms (71 mVpeak) into 50 ohms and -13 dBm. On average, these signals produce a combined signal ten times as large at -3 dB and the rms voltage is about 150 mV. However, from time to time, the vectors for each individual signal add up, so you have to add the _voltages_ for that moment, so the maximum theoretical peak amplitude is 700 mV (10x71 mV), thus, a single silicon diode starts to conduct, causing all kinds of mixing products. True enough. Some friends of mine live near the transmitter site of AM broadcast transmitter of KMPC in the San Fernando Valley section of Los Angeles, CA. KMPC is the only high power station in the "Valley" at 50 KW _into_ the antenna. :-) Within a few blocks of the KMPC transmitter, ANYTHING is possible insofar as IMD products, from tube type to solid-state receivers, some telephones, a few computers, intercoms, etc. :-( Using two (or more) 1N4148 type diodes in series instead of a single diode in the each back to back pair, will prevent any diode conduction as long as the peak voltage is larger than 1,4 V in either direction. Good point. The maximum number of diodes in series is determined by the amount of voltage the following stages will tolerate without disintegrating. :-) I once had a zener that became a sort of LED on a breadboard. For about 5 seconds or so. Since most likely there will be some selectivity between this diode clipper and the first amplifier stage, the amplifier stage will never see voltages as the limiting voltages in normal operation, but the diodes will still cut out some abnormal peaks e.g. induced by lightnings. True enough, but an electrostatic pickup during a storm MAY reach as high as 200 Volts or so. That's a static charge effect during the build-up period for lightning. A friend of mine living in the mountains decided he would "scientifically" measure the electrostatic charge build-up with VTVM connected to a small strip-chart recorder on a long-wire antenna. Lived at a 4000 foot elevation. Observation resulted in the "200 V" value. Unfortunately, he had so much trouble with the cheap strip-chart recorder that storm season was over by the time he got the recorder working. :-( The diodes should not have any effect on anything but a few millivolts of any signal arriving on your antenna. A non-conducting diode simply shows a junction capacitance to the rest of the world. That's a minor reactive discontinuity to the antenna connection. Putting multiple diodes in series in the back to back combination also reduce the capacitances, since the capacitances in each string are in series. 2 pFd at 10 MHz is only an 8 KOhm reactance. Len Anderson retired (from regular hours) electronic engineer person |
In article , Paul Keinanen
writes: On 24 Sep 2003 22:04:07 GMT, (Avery Fineman) wrote: The effect should not be there with or without diodes, with or without any resistors...unless there is some VERY big RF source out of the receiver's tuning range that is supplying energy to the diodes and thus causing the "mixer" effect. It should also be noted that when several quite strong out of band signals are present at the antenna, say ten signals, each with S9+60 dB, which is 50 mVrms (71 mVpeak) into 50 ohms and -13 dBm. On average, these signals produce a combined signal ten times as large at -3 dB and the rms voltage is about 150 mV. However, from time to time, the vectors for each individual signal add up, so you have to add the _voltages_ for that moment, so the maximum theoretical peak amplitude is 700 mV (10x71 mV), thus, a single silicon diode starts to conduct, causing all kinds of mixing products. True enough. Some friends of mine live near the transmitter site of AM broadcast transmitter of KMPC in the San Fernando Valley section of Los Angeles, CA. KMPC is the only high power station in the "Valley" at 50 KW _into_ the antenna. :-) Within a few blocks of the KMPC transmitter, ANYTHING is possible insofar as IMD products, from tube type to solid-state receivers, some telephones, a few computers, intercoms, etc. :-( Using two (or more) 1N4148 type diodes in series instead of a single diode in the each back to back pair, will prevent any diode conduction as long as the peak voltage is larger than 1,4 V in either direction. Good point. The maximum number of diodes in series is determined by the amount of voltage the following stages will tolerate without disintegrating. :-) I once had a zener that became a sort of LED on a breadboard. For about 5 seconds or so. Since most likely there will be some selectivity between this diode clipper and the first amplifier stage, the amplifier stage will never see voltages as the limiting voltages in normal operation, but the diodes will still cut out some abnormal peaks e.g. induced by lightnings. True enough, but an electrostatic pickup during a storm MAY reach as high as 200 Volts or so. That's a static charge effect during the build-up period for lightning. A friend of mine living in the mountains decided he would "scientifically" measure the electrostatic charge build-up with VTVM connected to a small strip-chart recorder on a long-wire antenna. Lived at a 4000 foot elevation. Observation resulted in the "200 V" value. Unfortunately, he had so much trouble with the cheap strip-chart recorder that storm season was over by the time he got the recorder working. :-( The diodes should not have any effect on anything but a few millivolts of any signal arriving on your antenna. A non-conducting diode simply shows a junction capacitance to the rest of the world. That's a minor reactive discontinuity to the antenna connection. Putting multiple diodes in series in the back to back combination also reduce the capacitances, since the capacitances in each string are in series. 2 pFd at 10 MHz is only an 8 KOhm reactance. Len Anderson retired (from regular hours) electronic engineer person |
In article , Dick Carroll
writes: Kieren wrote: Back to back: Take your two diodes and install them in parallel, but with one 'pointing' in the opposite direction. The idea is that, because each diode will conduct when the voltage rises above it's threashold, it doesn't matter if the spike is positive or negative. A radio signal is highly unlikely to be powerful enough to force either diode to conduct (and if it did, they'll protect the RX front end). I don't think they'd help much however! You only have to think about the kind of potential in a static build-up to decide that you do not want to rely on a pair of diodes to keep everything calm. Once the static voltage builds to .7 volt one or the other diode will conduct and "bleed" it off. Of course that assumes that we're not talking of lightning-level static charge. In that case all bets are off. Not quite right. Semiconductor diodes will BEGIN conducting at lower voltages. Do a V-I curve of forward conduction polarity to see that. That's a simple test with a low voltage supply, a pot, a resistor, and a low-range voltmeter. Many HF and MF installations use an RF choke of sufficient impedance placed across the antenna terminals to provide a discharge path for all static voltages to be immediately shunted to ground without disturbing the received radio signal in any way. No static ever builds up on the antenna. All it takes is a small RF choke of sufficient impedance to be transparent at the frequency of interest. Not quite right. A reasonably-high value inductance in parallel with any antenna is "transparent" at DC (limited to DC resistance) but is a VERY high value of reactance at RF. X_L = 2 pi L. A 2.5 mHy RFC will have a reactance of 15.7 KOhms at 1 MHz. Even with a long-wire whose maximum impedance magnitude might reach 5 KOhms, the effect of paralleling such an RFC is negligible. [in parallel it would be 3.8 KOhms] At higher frequencies the inductive reactance is proportionally higher. What MIGHT happen, depending on the particular inductor, is that the inductor's self-resonance due to distributed capacity would defeat the high-frequency reactance. Above self-resonance the RFC would appear as a capacitor. Len Anderson retired (from regular hours) electronic engineer person |
In article , Dick Carroll
writes: Kieren wrote: Back to back: Take your two diodes and install them in parallel, but with one 'pointing' in the opposite direction. The idea is that, because each diode will conduct when the voltage rises above it's threashold, it doesn't matter if the spike is positive or negative. A radio signal is highly unlikely to be powerful enough to force either diode to conduct (and if it did, they'll protect the RX front end). I don't think they'd help much however! You only have to think about the kind of potential in a static build-up to decide that you do not want to rely on a pair of diodes to keep everything calm. Once the static voltage builds to .7 volt one or the other diode will conduct and "bleed" it off. Of course that assumes that we're not talking of lightning-level static charge. In that case all bets are off. Not quite right. Semiconductor diodes will BEGIN conducting at lower voltages. Do a V-I curve of forward conduction polarity to see that. That's a simple test with a low voltage supply, a pot, a resistor, and a low-range voltmeter. Many HF and MF installations use an RF choke of sufficient impedance placed across the antenna terminals to provide a discharge path for all static voltages to be immediately shunted to ground without disturbing the received radio signal in any way. No static ever builds up on the antenna. All it takes is a small RF choke of sufficient impedance to be transparent at the frequency of interest. Not quite right. A reasonably-high value inductance in parallel with any antenna is "transparent" at DC (limited to DC resistance) but is a VERY high value of reactance at RF. X_L = 2 pi L. A 2.5 mHy RFC will have a reactance of 15.7 KOhms at 1 MHz. Even with a long-wire whose maximum impedance magnitude might reach 5 KOhms, the effect of paralleling such an RFC is negligible. [in parallel it would be 3.8 KOhms] At higher frequencies the inductive reactance is proportionally higher. What MIGHT happen, depending on the particular inductor, is that the inductor's self-resonance due to distributed capacity would defeat the high-frequency reactance. Above self-resonance the RFC would appear as a capacitor. Len Anderson retired (from regular hours) electronic engineer person |
In article , Roy Lewallen
writes: Neon bulbs are curious critters. As you say, they have hysteresis -- a higher strike voltage than sustaining voltage. The company I worked for once used them as low current regulators here and there, as well as for static protection, so they bought or selected them to various specifications for strike and sustaining voltages. Tektronix. :-) I'm thoroughly familiar with the 53n and 54n Tek scopes and their "seriesed" power supplies. A rather good design concept in my later opinion. Used to calibrate them at Ramo-Wooldridge Standards Lab 1959-1961. According to the parts descriptions they were controlled-characteristic miniature neon pilot bulbs. That worked out rather well since I only had one problem among about 300 or so scopes at R-W...and that was due to the error amplifier (tube circuit), not the voltage reference of the neon. Much smaller than the common "high grade" VR tube, a 5651. The bulbs were commonly used as pilot lamps, but not when the supply was DC. (This lesson was learned the hard way, judging by company documents and app notes.) Depending on the supply impedance, the pilot bulb could become a relaxation oscillator, interfering with sensitive circuitry. Heh, Tektronix and several other manufacturers of the 1950-1960 period. General Electric had that problem in one piece of broadcast TV thing. Encountered that at WREX-TV in 1956, where it was messing about with the local color sub-carrier generator. I came in just as their day was ending. I'm glad those are nearly gone. Neons are a nice AC pilot bulb or night light where the minor heat and supply current is not a problem. Today is a whole different ballgame with logic supply voltage dropping to 3.3 VDC and rail supplies for op-amps down to 1.5 VDC. LEDs are now cheap, take less power, and have different colors. Neon lamps are rather fixed at orange. ESD built into many MOS ICs makes it much easier on designers and users and repair folks. Gotta love it now! :-) Len Anderson retired (from regular hours) electronic engineer person |
In article , Roy Lewallen
writes: Neon bulbs are curious critters. As you say, they have hysteresis -- a higher strike voltage than sustaining voltage. The company I worked for once used them as low current regulators here and there, as well as for static protection, so they bought or selected them to various specifications for strike and sustaining voltages. Tektronix. :-) I'm thoroughly familiar with the 53n and 54n Tek scopes and their "seriesed" power supplies. A rather good design concept in my later opinion. Used to calibrate them at Ramo-Wooldridge Standards Lab 1959-1961. According to the parts descriptions they were controlled-characteristic miniature neon pilot bulbs. That worked out rather well since I only had one problem among about 300 or so scopes at R-W...and that was due to the error amplifier (tube circuit), not the voltage reference of the neon. Much smaller than the common "high grade" VR tube, a 5651. The bulbs were commonly used as pilot lamps, but not when the supply was DC. (This lesson was learned the hard way, judging by company documents and app notes.) Depending on the supply impedance, the pilot bulb could become a relaxation oscillator, interfering with sensitive circuitry. Heh, Tektronix and several other manufacturers of the 1950-1960 period. General Electric had that problem in one piece of broadcast TV thing. Encountered that at WREX-TV in 1956, where it was messing about with the local color sub-carrier generator. I came in just as their day was ending. I'm glad those are nearly gone. Neons are a nice AC pilot bulb or night light where the minor heat and supply current is not a problem. Today is a whole different ballgame with logic supply voltage dropping to 3.3 VDC and rail supplies for op-amps down to 1.5 VDC. LEDs are now cheap, take less power, and have different colors. Neon lamps are rather fixed at orange. ESD built into many MOS ICs makes it much easier on designers and users and repair folks. Gotta love it now! :-) Len Anderson retired (from regular hours) electronic engineer person |
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