Lightning Arrestors Question
Hi,
Saw a picture somewhere of an in-line lightning protector for a HF radio receive only antenna. Coax style. Apparently has the typical gas tube, and when activated shorts the center conductor to the braid. Was wondering a bit about this. I seem to remember in the old days, there was always a third tap on these sort of things that you ran a solid ground to, e.g., a water pipe. Does merely shorting to the braid provide "good" protection ? Any thoughts would be appreciated. Also want to ask: what about voltage surges of a few hundred volts or so induced on an antenna lead from a nearby lightning strike perhaps .. The levels way below what would trip a gas tube I would imagine, but still more than enough to ruin a front end of a receiver. How does one protect against these without breaking the bank doing so ? Thanks, Bob |
Lightning Arrestors Question
"Robert11" wrote in
: Hi, Saw a picture somewhere of an in-line lightning protector for a HF radio receive only antenna. Coax style. Apparently has the typical gas tube, and when activated shorts the center conductor to the braid. Was wondering a bit about this. I seem to remember in the old days, there was always a third tap on these sort of things that you ran a solid ground to, e.g., a water pipe. Does merely shorting to the braid provide "good" protection ? Any thoughts would be appreciated. Also want to ask: what about voltage surges of a few hundred volts or so induced on an antenna lead from a nearby lightning strike perhaps . The levels way below what would trip a gas tube I would imagine, but still more than enough to ruin a front end of a receiver. There are two issues, the differential impulse, and the common mode impulse. The shunt gas discharge tube will fire on the differential impulse voltage, although relatively slowly, even if it includes a radioactive isotope to assist ionisation. More importantly perhaps is that there is likely to be a substantial common mode current impulse and that will induce a transient voltage gradient in your grounding system. That transient may cause potential differences across equipment interfaces generally, possibly sufficient to damage them. There is also a risk of injury or death to persons. The type of suppressor you describe does precious little to deal with the common mode current impulse. The 'third wire' assists shunting common mode current to ground before entering the equipment room. How does one protect against these without breaking the bank doing so ? Disconnect antenna conductors when not in use, and do not use them unless the probability of lighting is low? Owen |
Lightning Arrestors Question
Hi Bob,
It takes about 100 volts for the neon tube to strike. The back to back diodes in the receiver antenna input should protect against this. The duration of a lightning strike is so brief that insufficient heat will be generated to destroy the diodes. BUT The neon or any spark gap protection device cannot protect against a direct lightning strike, only a near miss. Shorting the coax centre to the braid may not be good electrical practice but will provide sufficient protection for all practical purposes against static build up and lightning strikes within around 100 yards from your antenna. When at sea in the merchant navy a similar system did withstand a direct hit while I was in the radio room. The whole room lit up with a blue glow and there was a terrific crash from the antenna switching box as the strike arced to the ground through the ship's superstructure. Probably helped to have 20,000 tons of steel in contact with the ocean! The receiver (Marconi Apollo - wadley loop tuning and digital frequency readout on nixie tubes) blanked for about 5 seconds and then came back. Marconi know how to build stuff in those days. :-) Any protection is better than nothing, a spark gap (old automobile spark plug) or small neon tube, a couple of back to back diodes and a 5 megohm or higher resistor across the diodes to provide a static discharge path will do the job for pennies. Regards Mike G0ULI "Robert11" wrote in message ... Hi, Saw a picture somewhere of an in-line lightning protector for a HF radio receive only antenna. Coax style. Apparently has the typical gas tube, and when activated shorts the center conductor to the braid. Was wondering a bit about this. I seem to remember in the old days, there was always a third tap on these sort of things that you ran a solid ground to, e.g., a water pipe. Does merely shorting to the braid provide "good" protection ? Any thoughts would be appreciated. Also want to ask: what about voltage surges of a few hundred volts or so induced on an antenna lead from a nearby lightning strike perhaps . The levels way below what would trip a gas tube I would imagine, but still more than enough to ruin a front end of a receiver. How does one protect against these without breaking the bank doing so ? Thanks, Bob |
Lightning Arrestors Question
"Mike Kaliski" wrote in
: .... Any protection is better than nothing, .... unless it lulls you into a false sense of security ... a spark gap (old automobile spark plug) or small neon tube, a couple of back to back diodes and a 5 megohm or higher resistor across the diodes to provide a static discharge path will do the job for pennies. as most of these may. I do recall taking an early (probably the first) Collins digitally tuned receiver to a coast radio station for evaluation. It had inverse parallel diodes across the RF amp input for protection of the FETs and was totally unusable as when the on-site 500kHz transmitter was keyed up, it wiped out all of the receivers (not just this one) with broadband noise. It took a few minutes to realise what was causing ALL of the ROs to hear the station callsign, not as a beat note, but as noise as if it was near to where they were listening and just needed to be tuned in. Whilst the Collins was connected to an antenna, it caused havoc, even if powered off! Beware of the effects of inverse parallel diodes across the antenna. Owen |
Lightning Arrestors Question
Hi Owen,
Point taken. The standard Marconi ship station fed the receive antenna through the back contacts of the key, so the receiver was always disconnected whenever the transmitter was operating. I remember having to pay about £15 extra for my CMOS TTL electronic keyer to be fitted with a changeover relay rather than direct keying so I could use it with the standard Marconi ship installation. Still working fine today after 34 years of use! I don't recall ever operating close enough to any other stations for the diodes to cause me a problem, although I did once upset a Russian warship when operating from Angola. My signals were apparently overloading their equipment... Regards Mike G0ULI "Owen Duffy" wrote in message ... "Mike Kaliski" wrote in : ... Any protection is better than nothing, ... unless it lulls you into a false sense of security ... a spark gap (old automobile spark plug) or small neon tube, a couple of back to back diodes and a 5 megohm or higher resistor across the diodes to provide a static discharge path will do the job for pennies. as most of these may. I do recall taking an early (probably the first) Collins digitally tuned receiver to a coast radio station for evaluation. It had inverse parallel diodes across the RF amp input for protection of the FETs and was totally unusable as when the on-site 500kHz transmitter was keyed up, it wiped out all of the receivers (not just this one) with broadband noise. It took a few minutes to realise what was causing ALL of the ROs to hear the station callsign, not as a beat note, but as noise as if it was near to where they were listening and just needed to be tuned in. Whilst the Collins was connected to an antenna, it caused havoc, even if powered off! Beware of the effects of inverse parallel diodes across the antenna. Owen |
Lightning Arrestors Question
On Sep 25, 3:20*pm, "Mike Kaliski" wrote:
Hi Owen, Point taken. The standard Marconi ship station fed the receive antenna through the back contacts of the key, so the receiver was always disconnected whenever the transmitter was operating. I remember having to pay about £15 extra for my CMOS TTL electronic keyer to be fitted with a changeover relay rather than direct keying so I could use it with the standard Marconi ship installation. Still working fine today after 34 years of use! I don't recall ever operating close enough to any other stations for the diodes to cause me a problem, although I did once upset a Russian warship when operating from Angola. My signals were apparently overloading their equipment... Regards Mike G0ULI "Owen Duffy" wrote in message ... "Mike Kaliski" wrote in : ... Any protection is better than nothing, ... unless it lulls you into a false sense of security ... a spark gap (old automobile spark plug) or small neon tube, a couple of back to back diodes and a 5 megohm or higher resistor across the diodes to provide a static discharge path will do the job for pennies. as most of these may. I do recall taking an early (probably the first) Collins digitally tuned receiver to a coast radio station for evaluation. It had inverse parallel diodes across the RF amp input for protection of the FETs and was totally unusable as when the on-site 500kHz transmitter was keyed up, it wiped out all of the receivers (not just this one) with broadband noise. It took a few minutes to realise what was causing ALL of the ROs to hear the station callsign, not as a beat note, but as noise as if it was near to where they were listening and just needed to be tuned in. Whilst the Collins was connected to an antenna, it caused havoc, even if powered off! Beware of the effects of inverse parallel diodes across the antenna. Owen I found that all very interesting. Mike stick around |
Lightning Arrestors Question
On Thu, 24 Sep 2009 15:15:01 -0400, "Robert11"
wrote: Saw a picture somewhere of an in-line lightning protector for a HF radio receive only antenna. Coax style. Apparently has the typical gas tube, and when activated shorts the center conductor to the braid. See: http://www.polyphaser.com/productdata.aspx?class=coax This is what I use on the local mountain top sites. http://www.polyphaser.com/cms_spol_app/Translations/English/B50.pdf Note that we don't have much lightening on the left coast, so I don't have much history on how well it works. The one site where we did take a nearby hit, managed to blow up some unprotected ethernet to coax translators, and some cheap sacrificial ethernet switches. Also, not all lightning protectors use a gas tube. I have an older Polyphaser with ZnO ceramic elements. When hit with sufficient energy, the ZnO expands and closes a gap. Polyphaser places 4 of these in series from the center conductor to ground. My guess(tm), is that when hit by lightning, one of them might stay shorted. 4 hits, and it's totally shorted and must be replaced. However, I'm not sure. I'll post a photo when I find it. Was wondering a bit about this. Articles on the subject. http://www.polyphaser.com/technical_notes.aspx Ham Radio protection: http://www.polyphaser.com/cms_spol_app/techdocs/Ham%20Radio.pdf See Pg 6 for some interesting comments on receiver protection. Quoting in part: Coax protectors should be units that have dc blocking on the center pin. This serves as a high pass filtering that prevents the lightning's low frequency energy from continuing to your equipment. The strike energy is picked off and diverted into the ground system in a controlled way. The dc blocking ensures the operation of the protector regardless of the input circuitry of the equipment. Did you know that spark gap protectors with dc continuity will not work on receivers and shunt fed duplexers? The shunt to ground inside a receiver (coil to ground for static draining) prevents the low frequency lightning energy from turning on the dc continuity protector. The coil shunts the energy to ground all right, but it is at the wrong place. If the coil can't handle the energy (half the coax surge energy is on the center pin), the coil will open up and the current will translate to a large open voltage source capable of arcing anywhere within the radio. I seem to remember in the old days, there was always a third tap on these sort of things that you ran a solid ground to, e.g., a water pipe. Yep. The current needs to go somewhere to get to ground. Best through a big fat wire ending in a good ground than through your equipment. Incidentally, a water pipe is not a decent ground for lightning protection. Does merely shorting to the braid provide "good" protection ? No. If lightning came down your coax cable and to shorted braid it must have a path to continue to ground. Just a shorted coax will send it through your equipment, probably through the AC power cords, and then through the house wiring. I've seen photos of the wall blown out when that happens. Bad idea. Polyphaser also suggests that a DC short in the radio is inadequate: http://www.polyphaser.com/cms_spol_app/techdocs/Built-in%20Coax.pdf Any thoughts would be appreciated. Also want to ask: what about voltage surges of a few hundred volts or so induced on an antenna lead from a nearby lightning strike perhaps . The levels way below what would trip a gas tube I would imagine, but still more than enough to ruin a front end of a receiver. A high value resistor should bleed off any charges. As others have suggested, a neon lamp and/or back to back diodes, should also work. How does one protect against these without breaking the bank doing so ? -- Jeff Liebermann 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558 |
Lightning Arrestors Question
How does one protect against these without breaking the bank doing so ? Go on Mousers web site and look at gas tubes made by Littelfuse. Go to Littelfuses web site from the link on Mousers site and check out the specs on gas tubes. Compare them to the specs on your $50-70 commercial lightning arrestor. Then note that what's in that little casting box is two coax connectors, one capacitor and one $2-3 gas tube and you have the answer to your question. Myth revealed. Rick K2XT |
Lightning Arrestors Question
On Mon, 28 Sep 2009 14:20:29 GMT, "Rick" wrote:
How does one protect against these without breaking the bank doing so ? Go on Mousers web site and look at gas tubes made by Littelfuse. Go to Littelfuses web site from the link on Mousers site and check out the specs on gas tubes. Compare them to the specs on your $50-70 commercial lightning arrestor. Then note that what's in that little casting box is two coax connectors, one capacitor and one $2-3 gas tube and you have the answer to your question. Myth revealed. Yep. Data sheets on the ceramic gas tubes by Littelfuse: http://www.littelfuse.com/searchresults.html?NN=0%3aTechnology%3a157 Inside a 900Mhz cellular lightning protector. The two wires are an interdigital bandpass filter: http://802.11junk.com/jeffl/pics/lightning/polyphaser-02.jpg I don't think these look like they were made by Littelfuse. Unfinished panel: http://802.11junk.com/jeffl/pics/lightning/panel.jpg Mostly CATV protectors. -- # Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060 # 831-336-2558 # http://802.11junk.com # http://www.LearnByDestroying.com AE6KS |
Lightning Arrestors Question
On Sep 28, 10:20*am, "Rick" wrote:
How does one protect against these without breaking the bank doing so ? Go on Mousers web site and look at gas tubes made by Littelfuse. *Go to Littelfuses web site from the link on Mousers site and check out the specs on gas tubes. *Compare them to the specs on your $50-70 commercial lightning arrestor. Then note that what's in that little casting box is two coax connectors, one capacitor and one $2-3 gas tube and you have the answer to your question. Myth revealed. Rick * K2XT Rick or anyone else for that matter. Can anyone suggest a strategy for reasonably safe operation of a station when lightning is actually present in the area. The stations located at the weather service offices are used to receive real time weather reports from AROs. If they go off the air during lightning events the whole network becomes useless to the weather service. Television and radio stations continue to operate even after direct strikes to their antennas so it must be possible to provide protection that does not involve shutting down when lightning is present. Can anyone draw me a written sketch of how that gets done so that I can make a more knowledgeable decision on whether or not to try to replicate the technique. -- Tom Horne |
Lightning Arrestors Question
Basic strategy
Tom Horne wrote: On Sep 28, 10:20 am, "Rick" wrote: How does one protect against these without breaking the bank doing so ? Go on Mousers web site and look at gas tubes made by Littelfuse. Go to Littelfuses web site from the link on Mousers site and check out the specs on gas tubes. Compare them to the specs on your $50-70 commercial lightning arrestor. Then note that what's in that little casting box is two coax connectors, one capacitor and one $2-3 gas tube and you have the answer to your question. Myth revealed. Rick K2XT Rick or anyone else for that matter. Can anyone suggest a strategy for reasonably safe operation of a station when lightning is actually present in the area. The stations located at the weather service offices are used to receive real time weather reports from AROs. If they go off the air during lightning events the whole network becomes useless to the weather service. Television and radio stations continue to operate even after direct strikes to their antennas so it must be possible to provide protection that does not involve shutting down when lightning is present. Can anyone draw me a written sketch of how that gets done so that I can make a more knowledgeable decision on whether or not to try to replicate the technique. -- Tom Horne Hi Tom. In general, remember that all lightning strike issues, from cloud to ground or .. ground to cloud, depending on how things develop focus on on thing. The radio wave which is produced by the affair is trying to distribute itself over the surface of the earth in the area of the strike point. Recall that radio waves travel over the surface of the conductor involved. Thus, for example, the tower, pole, tree, building or whatever is the strike point is a conductor, good or bad, which is going to be used to carry the wave to the surface of the earth at that point. Then the wave expects to travel outward on the surface of the earth away from the focal point of the conductor until the energy of the wave is used up. OK, think this way. A more or less usual lower frequency tower for an AM station in the 500-1650Khz band is actually built so that the metal tower is directly grounded at the earth surface. At the 1Mhz point, the tower height for a quarter wave tower is around 250 feet high. Actually, at the bottom of the tower there is usually a metal plate that spreads out over the surface of the earth that is tied to the tower bottom, (Legs?). As well, for transmitter antenna purposes, there are also a more or less standard 120 copper wires that go out like spokes in a wagon wheel at or just below the surface of the earth there too. That means, very much surely, any lightning strike which hits that tower has a WONDERFUL way to go to the surface of the earth, then spread out over the surface away from the tower. The trick at this point is to keep the lightning strike from going on into the radio station from there. On a quarter wave length high tower, the conventional way to couple the transmitter to the tower is at the base to move out a little way from the tower, go up a little way with a separate wire, then couple the feed line to the tower via what is called a shunt feed system. It typically has a capacitor in series with the coaxial cable center conductor. And .. in all cases, the cable that goes back to the station will be close to or .. even in some cases under the surface of the earth for that run. The lightning protector will be out at the tower and will arc or flash the lightning bolt that might go down the feed line to the station so that it shorts the feed line for that split second for SURE to the earth and that collection of the metal plates and radial wires that make SURE the strike out over the surface of the earth and NOT back toward the station. As well, there is usually another lightning protector which does a similar job back where the feed line goes into the station as well. Using this technique, sure for a split second the station signal is shorted to ground when the strike is there. But it does NOT affect the station. Now .. fast forward to VHF TV, FM stations and HF shortwave stations. For towers for FM or TV stations, they may be MUCH higher, But the feed lines for the antenna or antennas on them are brought down the tower to GROUND level. There they are also put through lightning protector devices that do the same stunt of shunting the strike to the EARTH at the bottom of the tower. Then, the feed lines are send back to the station at, again, a same low level which protects them from carrying in the strike back to the station, as above. Variations of this sort of design are also present in on-building antenna systems that are done right to protect the equipment from strikes. One way or another the design ALWAYS should provide a VERY GOOD electrical path from the antenna to the earth, that is designed to have enough metal SURFACE to get the hit down to the earth without burning the conductor up. And again, this travels on the SURFACE of the wire, metal strip, pole or whatever. Bottom line. You always create a really good metal surface conductor that shunts things to the earth. And connect the feed line(s) for the antenna so that they are isolated from this good path to ground by bonding the shielding to the earth bound system, while providing a lightning protector to guarantee that the hit will pop to the ground bound side on a hit, while positioning the feed line so that it is a much less attractive path for the hit to go in to take down the equipment at or in the building. There are other things that are also of importance to a radio operation for protection from power line connected strikes, as well as overhead phone line strikes and copper wire cable system connections too. But, in general, the same details as above are in place for them too. My HF site gets hit at least two or three times directly every year. I operate right through thunderstorms, whatever in contests and have for decades now on 40 and 80 meter CW. With additional protection for the equipment this site is up 24X7 and hasn't lost a single radio, computer, modem, or ANYTHING for over 30 years now, though I also know enough to use isolation transformers and linear power supply computer systems, plus very carefully planned relay rack RF ground and surge protection techniques that do *NOT* use switching power supply CD voltage operations for computers and so on. W5WQN -- -- Sleep well; OS2's still awake! ;) Mike Luther |
Lightning Arrestors Question
Tom Horne wrote:
Can anyone suggest a strategy for reasonably safe operation of a station when lightning is actually present in the area. The stations located at the weather service offices are used to receive real time weather reports from AROs. If they go off the air during lightning events the whole network becomes useless to the weather service. Television and radio stations continue to operate even after direct strikes to their antennas so it must be possible to provide protection that does not involve shutting down when lightning is present. Can anyone draw me a written sketch of how that gets done so that I can make a more knowledgeable decision on whether or not to try to replicate the technique. Got to polyphaser's web site, read their white papers and contact them. Between them and Trans-Tector (they recently merged), they do antennas and power lines for things like air traffic control centers. Geoff. -- Geoffrey S. Mendelson, Jerusalem, Israel N3OWJ/4X1GM |
Lightning Arrestors Question
"Tom Horne" wrote ... On Sep 28, 10:20 am, "Rick" wrote: How does one protect against these without breaking the bank doing so ? Go on Mousers web site and look at gas tubes made by Littelfuse. Go to Littelfuses web site from the link on Mousers site and check out the specs on gas tubes. Compare them to the specs on your $50-70 commercial lightning arrestor. Then note that what's in that little casting box is two coax connectors, one capacitor and one $2-3 gas tube and you have the answer to your question. Myth revealed. Rick K2XT Rick or anyone else for that matter. Can anyone suggest a strategy for reasonably safe operation of a station when lightning is actually present in the area. The stations located at the weather service offices are used to receive real time weather reports from AROs. If they go off the air during lightning events the whole network becomes useless to the weather service. Television and radio stations continue to operate even after direct strikes to their antennas so it must be possible to provide protection that does not involve shutting down when lightning is present. Can anyone draw me a written sketch of how that gets done so that I can make a more knowledgeable decision on whether or not to try to replicate the technique. Here are the two ways. 1. Provocation of lightning strikes, or 2. Eliminating of lightning strikes. The instalation are the same only "tipping" is different. The blunt provocate and the sharp eliminate. Which is better I do not know. S* |
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