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Lightning Arrester
Anyone know how to make a simple lightning arrester (Homebrew) that really
work in case of lightning. |
Hang up "STOP" sign.
==================== Anyone know how to make a simple lightning arrester (Homebrew) that really work in case of lightning. |
"Mohd Nazry Bin Mustapa" wrote in message ... Anyone know how to make a simple lightning arrester (Homebrew) that really work in case of lightning. the most basic one is a spark gap. these have been used since the first days of long telegraph lines. just position two sharp pointed metal pieces a small distance apart, connect one side to the cable and the other to a good ground. you want the distance as small as possible, but wide enough so your normal transmission power doesn't create an arc. NOTE: a lightning arrester WILL NOT WORK if you don't have a good ground. IT IS NOT A REPLACEMENT FOR A GOOD GROUND SYSTEM! All a lightning arrester does is limit the voltage difference between signal carrying wires and the nearby ground it is connected to, you must properly connect all grounds together to get any benefit from any kind of lightning arrester. |
David Robbins wrote:
SNIP the most basic one is a spark gap. these have been used since the first days of long telegraph lines. just position two sharp pointed metal pieces a small distance apart, connect one side to the cable and the other to a good ground. you want the distance as small as possible, but wide enough so your normal transmission power doesn't create an arc. SNIP Remember, there is still a significant voltage across the spark gap before it ignites and during conduction. A 1/16 inch, or a 1.5 mm, gap will sustain ~1000 volts before igniting and support several hundreds of volts during conduction. The best solution, disconnect all antennas when not in use. DD, W1MCE |
"Mohd Nazry Bin Mustapa": Anyone know how to make a simple lightning arrester (Homebrew) that really work in case of lightning. "David Robbins": the most basic one is a spark gap. these have been used since the first days of long telegraph lines. just position two sharp pointed metal pieces a small distance apart, connect one side to the cable and the other to a good ground. you want the distance as small as possible, but wide enough so your normal transmission power doesn't create an arc. The usual practice for radio antennas is to place a series capacitor downstream (towards the radio set) from the spark gap to dispense with the DC and low-frequency components of the lightning strike. In crude, fixed-pitch ASCII art, it would look like this: | | Antenna ---------+--------| |----------- To Radio | | | SPARK V Blocking GAP ^ Capacitor | Ground ---------+---------------------- The size of the capacitor is a compromise between not disrupting the RF circuitry and coupling the low-frequecy energy from the strike into the radio. Making the capacitor reactance in the order of a few ohms at the lowest operating frequency generally should work for 50-ohm coax. Jim, K7JEB, Glendale, AZ |
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Antenna ---------+--------| |----------- To Radio | | | SPARK V Blocking GAP ^ Capacitor | Ground ---------+---------------------- PS: The breakdown voltage of the capacitor should be 10 times that of the spark gap. For a 1KV spark gap, that would give 10 KV. JEB |
There's no such thing. It's going to be a bit of work and money to do
anything effective. "Mohd Nazry Bin Mustapa" wrote in message ... Anyone know how to make a simple lightning arrester (Homebrew) that really work in case of lightning. |
K7JEB wrote:
| | Antenna ---------+--------| |----------- To Radio | | | SPARK V Blocking GAP ^ Capacitor | Ground ---------+---------------------- PS: The breakdown voltage of the capacitor should be 10 times that of the spark gap. For a 1KV spark gap, that would give 10 KV. JEB 2uF at 10kV, quite a capacitor. That would be 6 ohms or so on topband. As I understand it, there is nothing that can work if a direct lightening strike occurs. We are talking megavolts and thousands of amps. Way beyond anything an amateur could build. The best we can hope for is to dissipate charge build up on the aerial and ensure that there is no more than a kilovolt or so at the input to the rig caused by the (field) effects of a nearby strike. A spark gap that can conduct a lightening strike would be the size of a small truck. The only way to make sure you have a working station after a lightening strike on your aerials is to take out good insurance. vy 73 Andy, M1EBV |
Mohd Nazry Mustapa wrote:
"Anyone know how to make a simple lightning arrester (Homebrew) that really work in case of lightning?" I`ve found shorted (folded) antennas are less susceptible to lightning overload than are open-circuit antennas. A folded VHF monopole fed by coax and well grounded at the tower top is nearly immune to lightning. Coax, inside, rejects common-mode propagation of lightning energy. Coax, outside, needs good grounding to make a good path around (bypass for) protected equipment. The equipment needs direct low-impedance grounding so that most surge energy is dropped across the coax, not the equipment. Coils of extra coax may be used to raise the impedance of the outside of the coax. Equipment is still vulnerable to excess differential voltage on the power wires. Perhaps, excess common-mode voltage too. Manufacturers make brute-force L-C pi-network low-pass filters for each power wire connected to the equipment. These can be homebrewed if desired. They are important in delaying the surge on the power source lines to give time for the arresters time to spark across, giving protection to the equipment. Arresters need to be fast acting and placed to protect line-to-line and line to ground. These low-pass filters and arrestors are suitable for power and control wires, not for antenna wires in most cases. I`ve used lots of gas tubes on audio and control lines but never on a coax cable where I believe they are superfluous. I`ve used tower lighting RF chokes for the inductor in the low-pass powerline filters to get the needed current carrying capability, and various breakdown devices on the input and outpur of the filter. MOV`s work well. They are fast and cheap but may require replacement at times. Power lines are susceptible to dangerous surges. Filters reduce the bandwidth of energy that must be handled by the suppressor, just as the folded antenna or short-circuit 1/4-wave stub across an antenna limits the bandwidth of lightning energy that it has to accept. Lightning and other related surges are just enormous noises. They can be suppressed with the same techniques used with weaker noise. The equipment must be sturdy to endure a lightning strike. Arresters may be compared to sturdy noise clippers. Best regards, Richard Harrison, KB5WZI |
Effective lightning protection can be done in the amatuer station for a
reasonable cost. Most though, don't do so. "Andy Cowley" wrote in message ... As I understand it, there is nothing that can work if a direct lightening strike occurs. |
CW wrote:
Effective lightning protection can be done in the amatuer station for a reasonable cost. Most though, don't do so. My costs have always been reasonable - I unplug the antenna when not in use. I don't use it during thunderstorms. I have lived in extreme lightning areas with zero problems. -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
CW wrote:
Effective lightning protection can be done in the amatuer station for a reasonable cost. Most though, don't do so. "Andy Cowley" wrote in message ... As I understand it, there is nothing that can work if a direct lightening strike occurs. How? How do you deal with thousands of amps? It's for certain sure that a simple spark gap will be blown to kingdom come in the first millisecond, so what happens in the next millisecond? and the one after........... I think your method must be untried, untested and 'whistling in the dark'. Andy, M1EBV |
Cecil Moore wrote:
CW wrote: Effective lightning protection can be done in the amatuer station for a reasonable cost. Most though, don't do so. My costs have always been reasonable - I unplug the antenna when not in use. I don't use it during thunderstorms. I have lived in extreme lightning areas with zero problems. All good stuff, Cecil, but I'd say that was lightening avoidance not protection. I still don't believe there is an effective method of lightening protection for an amateur station that will accept a direct strike and survive. Even your method would probably result in a fried antenna ;-) Hope you never find out! vy 73 Andy, M1EBV |
If it weren't possible, millions of dollars of radio equipment would go up
in smoke every year. There are places that, if you have a tower, you WILL get hit on a regular basis. If you would like to know something about it, do a search on this group for Gary Coughman. Also, take a look at the Polyphaser web site. Before you start accusing someone of not knowing what they are talking about, you would be well advised to ensure that it is not you that is ignorant. "Andy Cowley" wrote in message ... CW wrote: Effective lightning protection can be done in the amatuer station for a reasonable cost. Most though, don't do so. "Andy Cowley" wrote in message ... As I understand it, there is nothing that can work if a direct lightening strike occurs. How? How do you deal with thousands of amps? It's for certain sure that a simple spark gap will be blown to kingdom come in the first millisecond, so what happens in the next millisecond? and the one after........... I think your method must be untried, untested and 'whistling in the dark'. Andy, M1EBV |
Andy Cowley wrote:
All good stuff, Cecil, but I'd say that was lightening avoidance not protection. I still don't believe there is an effective method of lightening protection for an amateur station that will accept a direct strike and survive. Even your method would probably result in a fried antenna ;-) Hope you never find out! I've been back in Texas for about 5 years now and the only thing that has gotten fried was a five-foot-tall live oak tree, the shortest thing around. Go figure. It's still struggling to stay alive with half its branches dead and a burn mark down the trunk. -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
"Andy Cowley" wrote in message ... CW wrote: Effective lightning protection can be done in the amatuer station for a reasonable cost. Most though, don't do so. "Andy Cowley" wrote in message ... As I understand it, there is nothing that can work if a direct lightening strike occurs. How? How do you deal with thousands of amps? It's for certain sure that a simple spark gap will be blown to kingdom come in the first millisecond, so what happens in the next millisecond? and the one after........... I think your method must be untried, untested and 'whistling in the dark'. Andy, M1EBV lightning doesn't go on for milliseconds, 50 micro-seconds is a relatively long stroke. 30kA can go through a 12ga copper wire with no damage for 10-20 microseconds. in most cases there will actually be very little voltage between wires of a coax or twin lead just because their insulation will break down or the feedpoint of the antenna will arc over... both are naturally occuring spark gaps that actually work very well to protect equipment from direct strikes. assuming of course the tower and feedline have good grounds. where people have problems is they don't ground the shield of the coax to a single point ground along with the power lines, so they get differential voltages between grounds that has no place to go but through the equipment. properly grounded installations with relatively small arresters to limit voltage on the center conductor of the coax relative to the shield are very effective. for tube type receivers a simple spark gap is adequate, for transistorized stuff you may need lower voltage protection and should probably get something commercially made for the job. |
"David Robbins" wrote in message ... "Andy Cowley" wrote in message ... CW wrote: Effective lightning protection can be done in the amateur station for a reasonable cost. Most though, don't do so. "Andy Cowley" wrote in message ... As I understand it, there is nothing that can work if a direct lightening strike occurs. How? How do you deal with thousands of amps? It's for certain sure that a simple spark gap will be blown to kingdom come in the first millisecond, so what happens in the next millisecond? and the one after........... I think your method must be untried, untested and 'whistling in the dark'. Andy, M1EBV lightning doesn't go on for milliseconds, 50 micro-seconds is a relatively long stroke. 30kA can go through a 12ga copper wire with no damage for 10-20 microseconds. in most cases there will actually be very little voltage between wires of a coax or twin lead just because their insulation will break down or the feedpoint of the antenna will arc over... both are naturally occurring spark gaps that actually work very well to protect equipment from direct strikes. assuming of course the tower and feedline have good grounds. where people have problems is they don't ground the shield of the coax to a single point ground along with the power lines, so they get differential voltages between grounds that has no place to go but through the equipment. properly grounded installations with relatively small arresters to limit voltage on the center conductor of the coax relative to the shield are very effective. for tube type receivers a simple spark gap is adequate, for transistorized stuff you may need lower voltage protection and should probably get something commercially made for the job. I've seen a common spark plug used to provide a spark gap for antennas. Setting the gap to about .05 inches will conduct much of the current away from the down stream circuitry. Some have suggested a few turns of the Coax after the gap will provide enough inductance to deter conduction past the gap, but I haven't pursued that to establish it as fact. There is also the problem of causing an impedance mismatch with an inductance in the line. The gap being smaller than the spacing of the coax would seem to be enough to minimize damage. |
Andy Cowley wrote in message
As I understand it, there is nothing that can work if a direct lightening strike occurs. We are talking megavolts and thousands of amps. Way beyond anything an amateur could build. Sure, but for only a short duration. There is plenty the average ham can do to reduce damage. The best we can hope for is to dissipate charge build up on the aerial Useless....Not much hope in that tactic. and ensure that there is no more than a kilovolt or so at the input to the rig caused by the (field) effects of a nearby strike. Actually, I think just a run of coax itself will reduce the potential to a few hundred volts before it gets to the rig. A spark gap that can conduct a lightening strike would be the size of a small truck. A 10 gauge wire can safely conduct a lightning strike to ground. But you must have a good low resistance connection to ground. If not, the wire will be burnt toast. The only way to make sure you have a working station after a lightening strike on your aerials is to take out good insurance. Insurance won't do any good for the existing gear. Proper setup to avoid damage, or disconnecting is a better idea. I take strikes around here all the time. Two were direct strikes to my mast in the last 4 years. I had no damage at all to anything, and I was sitting 15 ft from the base of the mast both times at this puter. Didn't flinch at all. MK |
Andy Cowley wrote in message I still don't believe there is an effective method
of lightening protection for an amateur station that will accept a direct strike and survive. There is, but most hams don't do it. Costs money, and everything has to be set up just right. It's done the same way all other 24 hour radio/tv stations, etc do it. How many commercial radio stations have you heard that go off the air when lightning strikes their tower? Not many I bet. We would never have reliable broadcast TV in this town if that were the case.. :/ MK |
On Mon, 15 Dec 2003 13:51:49 -0600, Cecil Moore
wrote: Andy Cowley wrote: All good stuff, Cecil, but I'd say that was lightening avoidance not protection. I still don't believe there is an effective method of lightening protection for an amateur station that will accept a direct strike and survive. Even your method would probably result in a fried antenna ;-) Hope you never find out! I've been back in Texas for about 5 years now and the only thing that has gotten fried was a five-foot-tall live oak tree, the shortest thing around. Go figure. It's still struggling to stay alive with half its branches dead and a burn mark down the trunk. My system gets hit about 3 times a year. So far I've only lost the front end out of a 2-meter rig and some coax. Since installing the new tower I've not lost any radio gear, but I did get one computer fried. http://www.rogerhalstead.com/ham_files/tower.htm shows the tower and antennas, but not the ground system. There are currently 30, 8' ground rods and over 600 feet of bare #2 copper tying the whole works together. Unfortunately we had to have some septic work done. When digging out the tank they hooked the ground system. Pulled out a section of the basement wall and cracked a whole bunch of it. The wall is temporarily repaired, but we are going to have to replace the entire wall this coming season. IF you have a fast connection the view from the top of the tower http://www.rogerhalstead.com/ham_files/tower.htm panorama. It's over 19 megs and would take forever on dial up. Roger Halstead (K8RI & ARRL life member) (N833R, S# CD-2 Worlds oldest Debonair?) www.rogerhalstead.com Return address modified due to dumb virus checkers |
David Robbins wrote:
"Andy Cowley" wrote in message ... CW wrote: Effective lightning protection can be done in the amatuer station for a reasonable cost. Most though, don't do so. "Andy Cowley" wrote in message ... As I understand it, there is nothing that can work if a direct lightening strike occurs. How? How do you deal with thousands of amps? It's for certain sure that a simple spark gap will be blown to kingdom come in the first millisecond, so what happens in the next millisecond? and the one after........... I think your method must be untried, untested and 'whistling in the dark'. Andy, M1EBV lightning doesn't go on for milliseconds, 50 micro-seconds is a relatively long stroke. 30kA can go through a 12ga copper wire with no damage for 10-20 microseconds. in most cases there will actually be very little voltage between wires of a coax or twin lead just because their insulation will break down or the feedpoint of the antenna will arc over... both are naturally occuring spark gaps that actually work very well to protect equipment from direct strikes. assuming of course the tower and feedline have good grounds. where people have problems is they don't ground the shield of the coax to a single point ground along with the power lines, so they get differential voltages between grounds that has no place to go but through the equipment. properly grounded installations with relatively small arresters to limit voltage on the center conductor of the coax relative to the shield are very effective. for tube type receivers a simple spark gap is adequate, for transistorized stuff you may need lower voltage protection and should probably get something commercially made for the job. I had not realised that the current was so 'spikey' I was aware that the duration of a stroke, including restrikes, was of the order of a second for large strikes. I found this info: 0.2 MA for 200 uS, then ~10 kA for another 200 uS, then 300-500 A for ~0.75 seconds. This followed by an average of 3 to 4 (max 26) restrikes at 0.1 MA (possibly decaying to 25 kA) for 200 uS for a big stroke. There is a MIL standard for this - MIL-STD-464. If your Coax breaks down then you have a PD in the tens of kV range for common coax and arc over in solid dielectric is permanently damaging. Sorry if I mislead anyone but we don't really suffer badly from lightning in G-land. Here are some interesting links. http://www.weighing-systems.com/Tech...Lightning1.pdf http://www.lightningsafety.com/nlsi_lhm/NFP_780.html http://www.mil-std-464.com/ http://www.kolacki.com/MIL-STD-464.htm I'm a little wiser now. Thanks vy 73 Andy, M1EBV |
Mark Keith wrote:
"There is plenty the average ham can do to reduce damage." True, and the ham needs a good ground anyway. Most commercial radio installations operate 24-7 and are nearly unaffected by lightning. Protection comes from common-sense lay out and usually does not include many expensive arresters. One arrester salesman said his business was exemplified by the story of a bar patron who had a pipe on a lanyard about his neck. Bartender asked about the thing pending from his neck. Client said it was an elephant whistle. Bar tender asked why? as no elephants were to be found in the environs. Bar patron says: See, it works doesn`t it? Best regards, Richard Harrison, KB5WZI |
David Robbins wrote:
SNIP lightning doesn't go on for milliseconds, SNIP. More specific information. The continuing portion of a lightning stroke, values up to 600 amperes, can go on for almost 300 milliseconds. Reference, WS-118-41129, Paragraph 3.9.XX [XX= I forgot the sub paragraph], Lightning [USAF system specification for the WS-118 Missile]. There is a USAF model, released in 1982, that encompasses 90% of all USA lightning strokes. It is as follows: Peak stroke; 0 to 100,000 amperes in 1 microsecond. Peak decay; 100,000 amperes to 25,000 amperes in 25 microseconds First tail; 25,000 amperes decaying to 600 amperes in 1 millisecond Continuing current; 600 amperes constant for 300 milliseconds. There may be up to 6 continuing strikes with amplitudes at 1/4 to 1/2 of the above. 50 micro-seconds is a relatively long stroke. 30kA can go through a 12ga copper wire with no damage for 10-20 microseconds. in most cases there will actually be very little voltage between wires of a coax or twin lead just because their insulation will break down or the feedpoint of the antenna will arc over SNIP: Arcs can sustain 100s of volts in the dynamics of the arc [plasma or carbonized material]. .... both are naturally occuring spark gaps that actually work very well to protect equipment from direct strikes. assuming of course the tower and feedline have good grounds. where people have problems is they don't ground the shield of the coax to a single point ground along with the power lines, so they get differential voltages between grounds that has no place to go but through the equipment. SNIP: Great advice! properly grounded installations with relatively small arresters to limit voltage on the center conductor of the coax relative to the shield are very effective. for tube type receivers a simple spark gap is adequate, for transistorized stuff you may need lower voltage protection and should probably get something commercially made for the job. SNIP: for a high power solid state station, 1500 watts, the matched RMS voltage is 274 volts, the maximum peak to peak is 274*2.828 = 774 volts p-p. Any surge device must accommodate the high RMS voltage and yet the receiver/transceiver front end must tolerate 774 volts p-p without damage. My solution, disconnect the antennas, radio power lines, etc. Deacon Dave, W1MCE |
Richard, the local radio station has a line to ground with a large gap
which regularly arcs because of static build up. Most radio stations go off the air momentarily when lightning strikes. Is it the static arc that drives a disconnect relay for a few milli seconds and is this used as a primary protector for lightning? Regards Art (Richard Harrison) wrote in message ... Mark Keith wrote: "There is plenty the average ham can do to reduce damage." True, and the ham needs a good ground anyway. Most commercial radio installations operate 24-7 and are nearly unaffected by lightning. Protection comes from common-sense lay out and usually does not include many expensive arresters. One arrester salesman said his business was exemplified by the story of a bar patron who had a pipe on a lanyard about his neck. Bartender asked about the thing pending from his neck. Client said it was an elephant whistle. Bar tender asked why? as no elephants were to be found in the environs. Bar patron says: See, it works doesn`t it? Best regards, Richard Harrison, KB5WZI |
Art, Kb9MZ wrote:
"---the local radio station has a line to ground with a large gap which regularly arcs because of static build up. Most stations go off the air momentarily when lightning strikes.' AM broadcasters use unbalanced vertical radiators driven against a ground radial system. The vertical radiator is nowdays the insulated tower irself. It sits on a base insulator, held erect by insulated guy wires. An arc-gap is fitted across the base insulator. This is either a pair of spheres or a pair of boomerang forms which are adjusted for a close spacing. Though galvanized, these gap fixtures get tower paint applications. Towers often get direct lightning hits. The paint remains pristene in all the gaps I`ve seen. The arc to ground is always to the Faraday shield between the tower coupling coils. That picket fence between the coils is pock marked like the face of the moon from tower strikes. Splattered copper abounds. You hear momentary disconnects during lightning strikes when listening to an AM station during this kind of storm. This is a defense mechanism. When lightning creates an arc, the conductive plasma path allows RF to continue feeding the ionization. This allows an arc to keep alive that the r-f is too feeble to strike for itself. Transmitter output into the plasma short circuit is an overload capable of transmitter damage. To counter the arc problem, the coax is d-c isolated with capacitors at the ends of the center conductor. The close-spaced coax usually gets an arc when the antenna system is overloaded. The coax has a high common-mode impedance. A relay d-c power supply and a d-c relay coil are connected in series and this series combination is connected between the center conductor and coax shield. An arc completes the d-c path for the relay coil. Relay activation is used to momentarily kill the transmitter, extinguishing the arc. Best regards, Richard Harrison, KB5WZI |
"Andy Cowley" wrote Here are some interesting
links. http://www.weighing-systems.com/Tech...Lightning1.pdf http://www.lightningsafety.com/nlsi_lhm/NFP_780.html http://www.kolacki.com/MIL-STD-464.htm Excellent reading, thanks. And thanks to all who contributed. In all these informative discussions, the precautions seem to be centered only around towers. My HF antennas consist of 3 long wires and 1 dipole suspended from and between pine trees, all some 80' in the air. Of course disconnecting constantly in thunderstorm season works, but should the feedlines all be connected to a ground system outside at time of disconnect? Is grounding a dipole for instance just guaranteeing a fry job when there might have been only dielectric-puncture? The latter is certainly an easer repair. I would think grounding might help to disintegrate the Balun also - but you guys are clearly the experts so I look forward to your advice. As far as rooftop antennas go, I now plan a much better down conductor system than the rado shack aluminum ground wires that probably melt just a wee bit slower than solder ;-) Jack Virginia Beach |
Sorry if this doubles, it didn't show up after almost an hour the 1st time:
"Andy Cowley" wrote Here are some interesting links. http://www.weighing-systems.com/Tech...Lightning1.pdf http://www.lightningsafety.com/nlsi_lhm/NFP_780.html http://www.kolacki.com/MIL-STD-464.htm Excellent reading, thanks. And thanks to all who contributed. In all these informative discussions, the precautions seem to be centered only around towers. My HF antennas consist of 3 long wires and 1 dipole suspended from and between pine trees, all some 80' in the air. Of course disconnecting constantly in thunderstorm season works, but should the feedlines all be connected to a ground system outside at time of disconnect? Is grounding a dipole for instance just guaranteeing a fry job when there might have been only dielectric-puncture? The latter is certainly an easer repair. I would think grounding might help to disintegrate the Balun also - but you guys are clearly the experts so I look forward to your advice. As far as rooftop antennas go, I now plan a much better down conductor system than the rado shack aluminum ground wires that probably melt just a wee bit slower than solder ;-) Jack Virginia Beach |
On Wed, 17 Dec 2003 00:05:58 -0500, "Jack Painter"
wrote: "Andy Cowley" wrote Here are some interesting links. http://www.weighing-systems.com/Tech...Lightning1.pdf http://www.lightningsafety.com/nlsi_lhm/NFP_780.html http://www.kolacki.com/MIL-STD-464.htm Excellent reading, thanks. And thanks to all who contributed. In all these informative discussions, the precautions seem to be centered only around towers. My HF antennas consist of 3 long wires and 1 dipole suspended from and between pine trees, all some 80' in the air. Of course disconnecting constantly in thunderstorm season works, but should the feedlines all be connected to a ground system outside at time of disconnect? Is grounding a dipole for instance just guaranteeing a fry job when there might have been only dielectric-puncture? The latter is certainly an easer repair. I would think grounding might help to disintegrate the Balun also - but you guys are clearly the experts so I look forward to your advice. As far as rooftop antennas go, I now plan a much better down conductor system than the rado shack aluminum ground wires that probably melt just a wee bit slower than solder ;-) Although some have already addressed part of the issue with wire antennas, I'll try to elaborate a bit without repeating...and will probably fail...but... Two things about ungrounded wire antennas and ungrounded verticals. Static electricity (precipitation static) and lightening strikes (nearby and direct hits) BE it rain of snow and snow is particularly bad, just the precipitation and build many thousands of volts on an antenna. Some years back...welllll...actually quite a few (back in 1966) I was in the process of living in a mobile home while building a new home. I had a 40 meter quarter was vertical set up about 100 feet from the trailer. The station was used on the kitchen counter and stored in a broom closet. One evening as we st there watching television I heard a popping noise. It was pretty loud. A bit of searching showed the noise to be coming from the closet. When I opened the door I was greeted by a blue white flash accompanied by a loud "pop". The static was arcing across the PL259 with enough current that the arc was extending a good half to one inch out from the connector and it put any ignition I've ever used to shame. That includes some pretty strong magnetos. To top it off the thing was flashing every few seconds. Now this was one of those things where the choke across the coax connector would have bled off the charge big as it was. A lightening arrestor (spark gap) would have kept the voltage down, but most likely would not have protected a receiver input without a choke across the connection. Nearby lightening strikes do something similar for ungrounded antennas although they also induce a current in grounded ones as well. Now we are getting into the realm where the choke across the terminals may not be enough to protect the rig and I'm assuming the rig is properly grounded. That a protective device across the input will protect the rig is some what problematic. It just depends on the strength of the induced voltage and current. OTOH, some protection is better than no protection. Now as to direct hits to wire antennas and ungrounded verticals. There are precautions to take such as cable routing and grounding of the shield at the base of the antenna and prior to entering the house/ham shack, but again these come with no guarantee. *Generally* installations using a few wire antennas and ungrounded verticals are configured in such a way that the antennas can be disconnected. With these stations I would always disconnect and ground the coax. Then unplug the AC mains from the station. I would resort to one other step which is to ground any other cables and even rotor cables if any exist. The easiest way to ground a group of coax cables is to take three aluminum plates (or copper). clamp the plates together and drill them to take bulkhead connectors (the clamping only assures the connectors will properly align after the thing is assembled.) One plate is for the connectors going into the house, one is for the coax cable connectors from the antennas and the third is for the grounding. I should really make one of these up and shoot some photos to show how well they can work. At any rate, The plates can be configured several ways as long as it allows the user to unplug the cables from the antennas from the house and plug it into the grounding plate. The slip on PL-259 equivalents work very well for this. The same thing can be done one cable at a time, but I find that with a rapidly approaching storm I'd not want to be spending time disconnecting one cable at a time and then reconnecting said cables to a grounded set of connectors. I'd go so far as to attach a pair of rack panel handles to the one plate to allow for easy unplugging and reinserting it into the grounding receptacle. I's also ground the metal plate that holds the feed throughs into the house and install PolyPhasers for each line. it and the grounding receptacle both need to be thoroughly grounded and make no sudden or sharp turns in the cables. Another tract would be to have all cables enter the house through a well grounded panel using bulkhead connectors and PolyPhaser. By well grounded I don't mean tieing the plate to a single ground rod with a #8 wire, but rather bonding the plate to at least two 8' ground rods and connecting those to a grounding network. Even then in this kind of installation I'd consider disconnecting the cables and grounding them. BTW, ground rods can be easy to install if you don't have rocky soils, by using a hydraulic drill. (Another thing I need to write up and photograph). Actually I have the photos. I just need to write up how to make and use one. Maybe soon. Roger Halstead (K8RI & ARRL life member) (N833R, S# CD-2 Worlds oldest Debonair?) www.rogerhalstead.com Return address modified due to dumb virus checkers Roger Halstead (K8RI & ARRL life member) (N833R, S# CD-2 Worlds oldest Debonair?) www.rogerhalstead.com Return address modified due to dumb virus checkers Jack Virginia Beach |
Jack wrote:
"My HF antennas consist of 3 long wires and 1 dipole suspended from and between pine trees, all some 80 feet in the air." I worked for years in a shortwave broadcasting plant. One building contained 12 transmitters, 8ea. 50KW, and 4ea 100 KW, plus several lower powered transmitters. We had dozens of antennas which included several curtain antennas for each of 3 frequency ranges, low, medium, and high. The curtain array requires 4 towers for support. It has 4 dipoles in a radiating plane, all driven in-phase. It has 4 reflecting dipoles in a parallel plane directly behind the radiators. Height of the drive point of the array, its midpoint, was about 1-WL, or about 165 feet as I recall. That makes the tower height well over 300 ffeet at 6 MHz. For economy, the curtains for a particular frequency range are hung from a double row of towers which support curtains on both sides. The transmission lines from nearly all antennas, curtains, rhombics, or whatever, are brought into a cross-bar switching area so that any transmitter can be connected to any antenna. Transmission lines are all open-wire spaced at about 15 inches, or more, for a 600-ohm impedance if memory serves. Where the antenna line enters the switching area, boomerang arc gaps provide a flashover-point opportunity, line-to-line, and line to ground.This works. Open wires, like coax, have a high common-mode impedance. This tends to make a gap more conducive than the transmission line. Use large ground wires to keep inductance and resistance low. This keeps voltage drop low and handles the kiloamps for the short period of the surge. Best regards, Richard Harrison, KB5WZI |
Dave Shrader wrote:
SNIP SNIP SNIP: for a high power solid state station, 1500 watts, the matched RMS voltage is 274 volts, the maximum peak to peak is 274*2.828 = 774 volts p-p. Any surge device must accommodate the high RMS voltage and yet the receiver/transceiver front end must tolerate 774 volts p-p without damage. Deacon Dave, W1MCE I gently disagree with your inclusion of the word receiver (with respect to tolerating 774 volts). That's why the T/R switch has an isolation spec that is much greater than 0dB. In receive mode the transceiver might be damaged by voltages much less than 774 volts. To confirm, simply transmit 1500 watts into your receiver. Your analysis is probably more-or-less valid for 1500 watt transmitters (or similar transceivers when transmitting). Unfortunately, most transceivers have a very high duty cycle for being in receive mode. |
You sniped his last staement. He concluded by this that no protection scheme
was going to help, other than disconecting, as that voltage would damage the reciever. "J. Harvey" wrote in message om... Dave Shrader wrote: SNIP SNIP SNIP: for a high power solid state station, 1500 watts, the matched RMS voltage is 274 volts, the maximum peak to peak is 274*2.828 = 774 volts p-p. Any surge device must accommodate the high RMS voltage and yet the receiver/transceiver front end must tolerate 774 volts p-p without damage. Deacon Dave, W1MCE I gently disagree with your inclusion of the word receiver (with respect to tolerating 774 volts). That's why the T/R switch has an isolation spec that is much greater than 0dB. In receive mode the transceiver might be damaged by voltages much less than 774 volts. To confirm, simply transmit 1500 watts into your receiver. Your analysis is probably more-or-less valid for 1500 watt transmitters (or similar transceivers when transmitting). Unfortunately, most transceivers have a very high duty cycle for being in receive mode. |
"CW" wrote:
You snipped his last statement. He concluded by this that no protection scheme was going to help, other than disconecting, as that voltage would damage the receiver. You're right - I misinterpreted his statement. I failed to notice that he intended the word 'must' to represent an impossible (or at least difficult) requirement. Regards. |
"Andy Cowley" wrote in message ... strike. A spark gap that can conduct a lightening strike would be the size of a small truck. The only way to make sure you have a working station after a lightening strike on your aerials is to take out good insurance. vy 73 Andy, M1EBV Nonsense. Every insulated AM broadcast station antenna has an arc gap at the base. How many stations get struck by lightning each year and keep on operating? Pete |
Uncle Peter wrote:
Every insulated AM broadcast station antenna has an arc gap at the base. How many stations get struck by lightning each year and keep on operating? 1732? -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
I would like to advise that an AM Broadcast station and an Amateur
station have at least one significant difference. The AM Station is most likely running a vacuum tube amplifier at high voltages with high voltage capacitors in the output stage. Also, they do not have a solid state receiver connected to the same transmission line. Therefore, they have a high tolerance to peak voltages. Most Amateur stations, excluding members of the Kilowatt Alley Society, have solid state finals and very sensitive solid state receiver circuits that do not have KV level tolerance to transient voltages. Conclusion, your argument is not totally valid! Deacon Dave, W1MCE Uncle Peter wrote: "Andy Cowley" wrote in message ... strike. A spark gap that can conduct a lightening strike would be the size of a small truck. The only way to make sure you have a working station after a lightening strike on your aerials is to take out good insurance. vy 73 Andy, M1EBV Nonsense. Every insulated AM broadcast station antenna has an arc gap at the base. How many stations get struck by lightning each year and keep on operating? Pete |
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On Fri, 19 Dec 2003 23:09:28 GMT, Dave Shrader
wrote: I would like to advise that an AM Broadcast station and an Amateur station have at least one significant difference. The AM Station is most likely running a vacuum tube amplifier at high voltages with high voltage capacitors in the output stage. Also, they do not have a solid state receiver connected to the same transmission line. Therefore, they have a high tolerance to peak voltages. My tower gets hit on average about 3 times a year. In the last 19 years I've only lost the front end out of one receiver and had a piece of heliax blown out about 30 feet from the top of the tower. I rarely if ever, disconnect any equipment except the computers and with those I worry about the phone lines more than the radio station. In the same period I've lost three computers. Most Amateur stations, excluding members of the Kilowatt Alley Society, have solid state finals and very sensitive solid state receiver circuits that do not have KV level tolerance to transient voltages. I have two KW amps hooked up to two different systems with 4 solid state transceivers connected to the antennas. The HF rigs are connected to the antennas through the relays in the KW amps. So the receivers are always on the antennas except when transmitting. Other than the amps everything here is solid state. One of the antenna systems is near the bottom of http://www.rogerhalstead.com/ham_files/tower.htm here's a bit about the ground system: http://www.rogerhalstead.com/ham_files/ground.htm Conclusion, your argument is not totally valid! Works for me, or has so far. Roger Halstead (K8RI & ARRL life member) (N833R, S# CD-2 Worlds oldest Debonair?) www.rogerhalstead.com Return address modified due to dumb virus checkers Deacon Dave, W1MCE Uncle Peter wrote: "Andy Cowley" wrote in message ... strike. A spark gap that can conduct a lightening strike would be the size of a small truck. The only way to make sure you have a working station after a lightening strike on your aerials is to take out good insurance. vy 73 Andy, M1EBV Nonsense. Every insulated AM broadcast station antenna has an arc gap at the base. How many stations get struck by lightning each year and keep on operating? Pete |
On Fri, 19 Dec 2003 15:07:07 -0500, " Uncle Peter"
wrote: "Andy Cowley" wrote in message ... strike. A spark gap that can conduct a lightening strike would be the size of a small truck. Most damage comes from the voltage induced by nearby strikes rather than direct hits, so the spark gap doesn't have to be a monster. Devices like PolyPhasers keep the voltage across the coax to a low level. If they get poked too hard they short. If they get poked really hard they blow apart. I had one short about a year ago, but there was no damage to the equipment. OTOH the PolyPhaser is over $50. Still, it was a good trade. The rig on that line is a TM-V7A and it was on at the time of the strike. The only way to make sure you have a working station after a lightening strike on your aerials is to take out good insurance. In a way. It means you will eventually have a working station. OTOH there are no guarantee, but it never hurts to move the odds in your favor by using good grounding techniques and protective devices, or throwing the coax out the window. Roger Halstead (K8RI & ARRL life member) (N833R, S# CD-2 Worlds oldest Debonair?) www.rogerhalstead.com Return address modified due to dumb virus checkers vy 73 Andy, M1EBV Nonsense. Every insulated AM broadcast station antenna has an arc gap at the base. How many stations get struck by lightning each year and keep on operating? Pete |
Link coupling is possible with a Faraday shield on the link only.
The main tuning coils have a 'gap' of sufficient size to accommodate the link. The link is shielded. Back in the 'olden days', 1955, I used a shielded link from B&W in a 40 meter home brew project [a pair of 807s in PP]. Deacon Dave, W1MCE + + + |
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