Re: [time-nuts] Lightning arrestors for GPSDO antenna
Chris Albertson wrote: On Thu, Oct 16, 2014 at 7:51 PM, Dave M dgmin...@mediacombb.net wrote: Thanks, Chris. I've done a bit or research on the subject, and think I have a reasonable grip on the necessary steps. I have an 8' ground rod driven into the ground directly under the spot where my antennas mount. #6 solid copper from the rod to a heavy aluminum plate, where the arrestors will be mounted. A #6 solid copper wire from the plate to the antenna mounting structure. About the only thing you left out is the interconnection between this new ground rod and the existing house ground. Sounds like you must live in Florida. The best source of information is the lightening lab at University of FL. I've never read a good research backed paper on plastic v. metal conduit. I bet it does matter. I use iron pipe outdoors then after it gets indoors switch to plastic. Practical reasons. The flexible plastic conduit is just easier to use Actually, I lived in Florida for about 40 years, retiring to north Alabama about 5 years ago. about 6 of those years were spent working at a Motorola 2-way radio shop. So, yes, I'm pretty familiar with the damages that lightning can cause, and some of the precautions that help minimize susceptability and damage. As I posted earlier, I've seen writings promoting metallic and non-metallic conduit for the antenna coax. I can see reasons for placing the coax in metallic conduit. But, one thing that I've read that is consistent, is NOT to run the earth ground wire in metallic conduit. That's to keep the current to ground in a solid, unbroken path, which the fittings used to join conduit can't provide. OK to run it in non-metallic conduit to keep it out of the weather. Since my coax run is only about 20 ft, I'm thinking that I should be OK with the coax in 1/2 galvanized steel conduit. I agree that the metallic conduit should stay outside, and not be connected to the equipment ground inside. I'll run a separate ground wire from the equipment rack to the ground rod outside. Cheers, Dave M ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Lightning arrestors for GPSDO antenna
FWIW, when grounding the metal mast of a boat, three inch wide copper strap is used because it is a better RF conductor. The strap is available in marine supply stores. You really don't want lightning punching one or more holes in your boat, so whatever hits the mast (usually the full stroke, not a side shoot) gets directed directly to the keel. IIRC, gas discharge tubes take some time to ignite, so something faster is required to take the initial current. Bill Hawkins -Original Message- From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of Dave M Sent: Saturday, October 18, 2014 12:48 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Lightning arrestors for GPSDO antenna Chris Albertson wrote: On Thu, Oct 16, 2014 at 7:51 PM, Dave M dgmin...@mediacombb.net wrote: Thanks, Chris. I've done a bit or research on the subject, and think I have a reasonable grip on the necessary steps. I have an 8' ground rod driven into the ground directly under the spot where my antennas mount. #6 solid copper from the rod to a heavy aluminum plate, where the arrestors will be mounted. A #6 solid copper wire from the plate to the antenna mounting structure. About the only thing you left out is the interconnection between this new ground rod and the existing house ground. Sounds like you must live in Florida. The best source of information is the lightening lab at University of FL. I've never read a good research backed paper on plastic v. metal conduit. I bet it does matter. I use iron pipe outdoors then after it gets indoors switch to plastic. Practical reasons. The flexible plastic conduit is just easier to use Actually, I lived in Florida for about 40 years, retiring to north Alabama about 5 years ago. about 6 of those years were spent working at a Motorola 2-way radio shop. So, yes, I'm pretty familiar with the damages that lightning can cause, and some of the precautions that help minimize susceptability and damage. As I posted earlier, I've seen writings promoting metallic and non-metallic conduit for the antenna coax. I can see reasons for placing the coax in metallic conduit. But, one thing that I've read that is consistent, is NOT to run the earth ground wire in metallic conduit. That's to keep the current to ground in a solid, unbroken path, which the fittings used to join conduit can't provide. OK to run it in non-metallic conduit to keep it out of the weather. Since my coax run is only about 20 ft, I'm thinking that I should be OK with the coax in 1/2 galvanized steel conduit. I agree that the metallic conduit should stay outside, and not be connected to the equipment ground inside. I'll run a separate ground wire from the equipment rack to the ground rod outside. Cheers, Dave M ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Lightning arrestors for GPSDO antenna
On 10/18/14, 2:05 PM, Bill Hawkins wrote: FWIW, when grounding the metal mast of a boat, three inch wide copper strap is used because it is a better RF conductor. The strap is available in marine supply stores. It's actually more about being convenient to install, and tradition. If you have a 1 square centimeter conductor at 1x1 cm, the inductance is about 1.5 uH/meter, and when it's 10cmx 1mm (4 wide) the inductance is 1.15 uH/meter. That's not a big difference in the voltage due to a transient. What does go down dramatically (at frequencies where the skin effect thickness is small) is the AC resistance, which will be 0.2 for the 10x0.1 (20cm perimeter) relative to the 1x1 bar (4 cm perimeter). Skin depth in copper at 1 MHz is about 0.06mm. so the bar has a effective RF cross-section of 2.4 square mm, for a AC resistance of about 7 milliOhm/meter. However, for lightning, with rise times in the microsecond range (e.g. MHz kind of frequency), the voltage due to inductance is huge (1 uH/meter * 10 kA/microsecond = 10kV/meter) compared to the voltage due to resistance (10kA*7mOhm/m = 70V/meter) Now, if that strap is part of an RF ground for your transmitting antenna, then the lower resistance of the strap is a good thing. Inductance is lossless, but AC resistance sure isn't. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Lightning arrestors for GPSDO antenna
John Allen wrote: Hello All - There is a 500+ page document on grounding, lightning protection and more - Google for: STANDARDS AND GUIDELINES FOR COMMUNICATION SITES Motorola R56 2005 Regards, John K1AE Great document! Thanks for the link Dave M ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Lightning arrestors for GPSDO antenna
If anyone is interested, I have a few NOS Zap-Tech 30-105 (now called CX-TF apparently) surge suppressors available. These are basically a single shunt gas tube (the coaxial center conductor runs through the center of a custom gas tube), and they were sold as GPS in-line suppressors. I use them at the far end of the rf spectrum: all of my receive-only wire antennas (Beverages) for 1.8-7 MHz have one on each feedline where they enter the house. These antennas are up to 800' long, and I know for a fact they pick up surges from every passing storm and, so far, the elephants have stayed away... ;-) These units have TNC female adapters on both ends, but if the TNCs are screwed off (they are loc-tite'd on), there are F-female connectors underneath. $20 will get one mailed in the US. 73, geo - n4ua On Fri, Oct 17, 2014 at 1:23 AM, ed breya e...@telight.com wrote: Of all device types, I think gas tubes are the best for this sort of application - very low C, and high surge current rating. I'm picturing the kind that are used in power supplies and such for limiting line transients - about 1 cm dia and length with axial leads. I don't know what kind are used in lightning arrestors, if they are the same or scaled up in size. Whether you make it able to take a direct hit depends on how big of a hit, your budget, and the environment of the antenna and lines. If it's the tallest thing in a huge field in a lightning-prone area, then it could be a big issue, but I don't think most people have that situation. You may want to look at the US National Electrical Code (NEC) for ideas - I believe that subject is covered there. The main thing there would be safety against injuries and fire, even if the equipment is destroyed. I think what you would want is kind of a pi network - the lowest impedance path to ground at the antenna zone that can be practically realized, then a high common-mode impedance (or even fusible) line to carry the signal to the building, then another low impedance path to ground at the building. This means that in my opinion, you should not put the feedline in metal conduit unless it's essential for protection - or underground, which should improve the grounding. You want the antenna zone to absorb the brunt of any discharge, then use the higher line Zcm to hopefully give some degree of isolation from there to the building. Ed ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/ mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Lightning arrestors for GPSDO antenna
Hello Dave, I think we had a similar question recently - and I have been told the PolyPhaser products are gas tubes - I haven't opened one up yet. TESSCO sells these online - you can find them here: https://www.tessco.com/products/displayProducts.do?groupId=90143subgroupId=91046 Regards, John W. On Thu, Oct 16, 2014 at 10:23 PM, ed breya e...@telight.com wrote: Of all device types, I think gas tubes are the best for this sort of application - very low C, and high surge current rating. I'm picturing the kind that are used in power supplies and such for limiting line transients - about 1 cm dia and length with axial leads. I don't know what kind are used in lightning arrestors, if they are the same or scaled up in size. Whether you make it able to take a direct hit depends on how big of a hit, your budget, and the environment of the antenna and lines. If it's the tallest thing in a huge field in a lightning-prone area, then it could be a big issue, but I don't think most people have that situation. You may want to look at the US National Electrical Code (NEC) for ideas - I believe that subject is covered there. The main thing there would be safety against injuries and fire, even if the equipment is destroyed. I think what you would want is kind of a pi network - the lowest impedance path to ground at the antenna zone that can be practically realized, then a high common-mode impedance (or even fusible) line to carry the signal to the building, then another low impedance path to ground at the building. This means that in my opinion, you should not put the feedline in metal conduit unless it's essential for protection - or underground, which should improve the grounding. You want the antenna zone to absorb the brunt of any discharge, then use the higher line Zcm to hopefully give some degree of isolation from there to the building. Ed ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/ mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Lightning arrestors for GPSDO antenna
On Thu, Oct 16, 2014 at 7:51 PM, Dave M dgmin...@mediacombb.net wrote: Thanks, Chris. I've done a bit or research on the subject, and think I have a reasonable grip on the necessary steps. I have an 8' ground rod driven into the ground directly under the spot where my antennas mount. #6 solid copper from the rod to a heavy aluminum plate, where the arrestors will be mounted. A #6 solid copper wire from the plate to the antenna mounting structure. About the only thing you left out is the interconnection between this new ground rod and the existing house ground. Sounds like you must live in Florida. The best source of information is the lightening lab at University of FL. I've never read a good research backed paper on plastic v. metal conduit. I bet it does matter. I use iron pipe outdoors then after it gets indoors switch to plastic. Practical reasons. The flexible plastic conduit is just easier to use -- Chris Albertson Redondo Beach, California ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Lightning arrestors for GPSDO antenna
On 10/17/14, 6:26 AM, Chris Albertson wrote: On Thu, Oct 16, 2014 at 7:51 PM, Dave M dgmin...@mediacombb.net wrote: Thanks, Chris. I've done a bit or research on the subject, and think I have a reasonable grip on the necessary steps. I have an 8' ground rod driven into the ground directly under the spot where my antennas mount. #6 solid copper from the rod to a heavy aluminum plate, where the arrestors will be mounted. A #6 solid copper wire from the plate to the antenna mounting structure. About the only thing you left out is the interconnection between this new ground rod and the existing house ground. Sounds like you must live in Florida. The best source of information is the lightening lab at University of FL. I've never read a good research backed paper on plastic v. metal conduit. You can use metal conduit as the bonding conductor between grounding systems, for one thing. I bet it does matter. I use iron pipe outdoors then after it gets indoors switch to plastic. Practical reasons. The flexible plastic conduit is just easier to use ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Lightning arrestors for GPSDO antenna
You can use metal conduit as the bonding conductor between grounding systems, for one thing. That works fine, but I think it is disallowed by the electrical code. If you used metallic conduit it MUST be grounded but you can't use it for grounding. That said, it does work. I think the danger the electric code addresses is that connections between conduit sections become loose over time and might corrode. I think the threaded conduit would work fine. That stuff is like water pipe but smoother inside. -- Chris Albertson Redondo Beach, California ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Lightning arrestors for GPSDO antenna
Dave, We have a 26 dB Lucent (TMG-HR-26NCM) antenna mounted on the gable end of the N2MO station. The feed line (1/2 superflex) runs straight down to a watertight steel box with a Polyphaser GPS protector. The superflex shield is tied to the ground with the standard Andrew kit. Both the antenna mounting pipe and protector have a #2 grounding wire to an 8' rod. When the ring ground is replaced we will weld it to existing rod from two directions. I can prove links to pictures if it helps. Martin Flynn . 26dB On Thu, Oct 16, 2014 at 4:34 PM, Dave M dgmin...@mediacombb.net wrote: I'm looking for effective coaxial lightning arrestors for my GPSDO antennas. I've seen several types; those completely enclosed in a one-piece metal enclosure (no replaceable components) and those having a replaceable gas discharge tube seem to predominate the list. I'm looking closely at the gas discharge tube types, and am curious as to their effectiveness and durability. I'd like to know stuff like; are they effective in dissipating a static charge, how do I know when the gas tube needs to be replaced, are the gas tubes of a special type, are replacement gas tube easily available, etc. I'm interested in opinions and experiences with arrestors and recommendations for which type is most effective. Thanks for comments, Dave M _ ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Lightning arrestors for GPSDO antenna
On 10/17/14, 8:17 AM, Chris Albertson wrote: You can use metal conduit as the bonding conductor between grounding systems, for one thing. That works fine, but I think it is disallowed by the electrical code. If you used metallic conduit it MUST be grounded but you can't use it for grounding. That said, it does work. I think the danger the electric code addresses is that connections between conduit sections become loose over time and might corrode. The metallic raceway (code speak for conduit) is allowed to be the bonding conductor (bonding conductor = greenwire or electrical safety ground in code speak). Properly installed conduit will have a good connection, etc.. When interconnecting multiple grounding electrodes or electrode systems is where the requirements for particular gauges of wire come in, and mostly it has to do with mechanical strength and reliability. You can use a smaller conductor if it is protected inside something, for instance. The other rule is that the bonding conductor has to be continuous (the concern you mentioned about connections becoming loose, etc). http://lightning.org/wp-content/uploads/2013/04/Bonding-2013-ULPA-LPI-rev1.pdf is a very nice summary Mike Holt (http://www.mikeholt.com/) has a great website on all code related issues, and he's written a bunch of articles that explain the code and the rationale behind the requirements. http://ecmweb.com/code-basics/grounding-and-bonding-part-1-3 And when it comes to antennas and the like, you're in a different section of the code 810, 820, and the requirements for the grounding conductor (and whether coax shield can be that grounding conductor) are all laid out there. In many case, the coax shield can serve as the grounding conductor, but only if there are no connectors in the path (i.e. you have to have a clamp that directly contacts the shield where it interconnects with the building grounding system). A barrel feedthrough in a grounded metal panel doesn't meet the strict requirements of the code (although personally, I think it's a fine solution) One thing to remember about the NEC requirements is that the threat they are protecting against with the grounding and bonding requirements is NOT a lightning strike. It's contact with an energized conductor (e.g. a power line touches your antenna or supporting structure). That's a whole lot more common (wind storms, etc.) NFPA 780 is the lightning protection code, and has a lot more lightning protection aspects. The NEC cares almost nothing about transient protection, the concern is more about electrical shocks and burning the building down. Furthermore, the NEC really only regulates the wiring in your building, and nothing that is connected to it, nor does it regulate the wiring of the power company. There are two tomes of reference I use for transient protection: one is IEEE 1100 (the Emerald Book) which has gone under many names over the years (politics.. computer manufacturers did not want their equipment described as sensitive electronic equipment) http://standards.ieee.org/findstds/standard/1100-2005.html The other is Protection of Electronic Circuits from Overvoltages by R.B. Standler. http://www.amazon.com/gp/search?index=bookslinkCode=qskeywords=9780486425528 http://store.doverpublications.com/0486425525.html And, if you're at the Dover Pubs store.. take a look at the books about lightning from Martin Uman. Very readable, lots of technical info. I think the threaded conduit would work fine. That stuff is like water pipe but smoother inside. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Lightning arrestors for GPSDO antenna
Hello All - There is a 500+ page document on grounding, lightning protection and more - Google for: STANDARDS AND GUIDELINES FOR COMMUNICATION SITES Motorola R56 2005 Regards, John K1AE ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Lightning arrestors for GPSDO antenna
All: Some very good information here. I use NFPA codes in my day job. JUST YESTERDAY, I learned that you can read their standards for free. Go to their site, and you'll see a link for free access to any of their standards. You can't save or print, but you can read. You will have to create an account, but they don't demand anything that isn't already public. 73, Jim wb4...@amsat.org On 10/17/2014 12:11 PM, Jim Lux wrote: On 10/17/14, 8:17 AM, Chris Albertson wrote: You can use metal conduit as the bonding conductor between grounding systems, for one thing. That works fine, but I think it is disallowed by the electrical code. If you used metallic conduit it MUST be grounded but you can't use it for grounding. That said, it does work. I think the danger the electric code addresses is that connections between conduit sections become loose over time and might corrode. The metallic raceway (code speak for conduit) is allowed to be the bonding conductor (bonding conductor = greenwire or electrical safety ground in code speak). Properly installed conduit will have a good connection, etc.. When interconnecting multiple grounding electrodes or electrode systems is where the requirements for particular gauges of wire come in, and mostly it has to do with mechanical strength and reliability. You can use a smaller conductor if it is protected inside something, for instance. The other rule is that the bonding conductor has to be continuous (the concern you mentioned about connections becoming loose, etc). http://lightning.org/wp-content/uploads/2013/04/Bonding-2013-ULPA-LPI-rev1.pdf is a very nice summary Mike Holt (http://www.mikeholt.com/) has a great website on all code related issues, and he's written a bunch of articles that explain the code and the rationale behind the requirements. http://ecmweb.com/code-basics/grounding-and-bonding-part-1-3 And when it comes to antennas and the like, you're in a different section of the code 810, 820, and the requirements for the grounding conductor (and whether coax shield can be that grounding conductor) are all laid out there. In many case, the coax shield can serve as the grounding conductor, but only if there are no connectors in the path (i.e. you have to have a clamp that directly contacts the shield where it interconnects with the building grounding system). A barrel feedthrough in a grounded metal panel doesn't meet the strict requirements of the code (although personally, I think it's a fine solution) One thing to remember about the NEC requirements is that the threat they are protecting against with the grounding and bonding requirements is NOT a lightning strike. It's contact with an energized conductor (e.g. a power line touches your antenna or supporting structure). That's a whole lot more common (wind storms, etc.) NFPA 780 is the lightning protection code, and has a lot more lightning protection aspects. The NEC cares almost nothing about transient protection, the concern is more about electrical shocks and burning the building down. Furthermore, the NEC really only regulates the wiring in your building, and nothing that is connected to it, nor does it regulate the wiring of the power company. There are two tomes of reference I use for transient protection: one is IEEE 1100 (the Emerald Book) which has gone under many names over the years (politics.. computer manufacturers did not want their equipment described as sensitive electronic equipment) http://standards.ieee.org/findstds/standard/1100-2005.html The other is Protection of Electronic Circuits from Overvoltages by R.B. Standler. http://www.amazon.com/gp/search?index=bookslinkCode=qskeywords=9780486425528 http://store.doverpublications.com/0486425525.html And, if you're at the Dover Pubs store.. take a look at the books about lightning from Martin Uman. Very readable, lots of technical info. I think the threaded conduit would work fine. That stuff is like water pipe but smoother inside. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. --- This email is free from viruses and malware because avast! Antivirus protection is active. http://www.avast.com ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Lightning arrestors for GPSDO antenna
Hi There are a number of them on the auction sites. They are fairly specific in terms of frequency band and application. Bob On Oct 16, 2014, at 7:34 PM, Dave M dgmin...@mediacombb.net wrote: I'm looking for effective coaxial lightning arrestors for my GPSDO antennas. I've seen several types; those completely enclosed in a one-piece metal enclosure (no replaceable components) and those having a replaceable gas discharge tube seem to predominate the list. I'm looking closely at the gas discharge tube types, and am curious as to their effectiveness and durability. I'd like to know stuff like; are they effective in dissipating a static charge, how do I know when the gas tube needs to be replaced, are the gas tubes of a special type, are replacement gas tube easily available, etc. I'm interested in opinions and experiences with arrestors and recommendations for which type is most effective. Thanks for comments, Dave M ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Lightning arrestors for GPSDO antenna
Lightening arrestors are an important part of a protection system but just installing some in the antenna cable is not going to help so much. You need a system approach. If you do it right you can take a direct hit The big problem with grounding is Ohm's Law. That is if any current flows in a conductor that has resistance there will be a voltage across the conductor equal to the current times the resistance. But with lightening you can have 100,000 amps of current in a ground wire. If that wires has 0.01 ohms of resistance you have 1,000 volts above true ground on your ground connector on the lightening arrestor. Your ground is no longer at ground. You need some very tiny resistances and to get that you are going to need to do things like using multiple ground rods and large conductors. And connecting grounds together. On Thu, Oct 16, 2014 at 4:34 PM, Dave M dgmin...@mediacombb.net wrote: I'm looking for effective coaxial lightning arrestors for my GPSDO antennas. I've seen several types; those completely enclosed in a one-piece metal enclosure (no replaceable components) and those having a replaceable gas discharge tube seem to predominate the list. I'm looking closely at the gas discharge tube types, and am curious as to their effectiveness and durability. I'd like to know stuff like; are they effective in dissipating a static charge, how do I know when the gas tube needs to be replaced, are the gas tubes of a special type, are replacement gas tube easily available, etc. I'm interested in opinions and experiences with arrestors and recommendations for which type is most effective. Thanks for comments, Dave M ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. -- Chris Albertson Redondo Beach, California ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Lightning arrestors for GPSDO antenna
Thanks, Chris. I've done a bit or research on the subject, and think I have a reasonable grip on the necessary steps. I have an 8' ground rod driven into the ground directly under the spot where my antennas mount. #6 solid copper from the rod to a heavy aluminum plate, where the arrestors will be mounted. A #6 solid copper wire from the plate to the antenna mounting structure. I will also have an arrestor at the antenna input of each GPSDO unit, which will be mounted on a 2 wide copper strap, which will be then run to the outside ground rod with a doubled 1 wide copper braid. I realize that extremely low ground resistance is fantastic, but I don't have access to a ground resistance set, so I'll have to accept what I have and accept the consequences if something happens. A second ground rod isn't out of the question, but will have to wait until my broken wrist heals so I can swing a sledge hammer. I'd still like to hear comments on the effectiveness of gas discharge type arrestors. A question has bothered me for a while, but can't find a definitive answer. Should I enclose the antenna feedline in metal conduit or nonmetal conduit? I've seen documents that state that metal conduit is the best way, and others stating that metal conduit shouldn't be used Anyone have a good answer (talking about antenna feedline; not the grounding wire)? Thanks, Dave M --- Chris Albertson wrote: Lightening arrestors are an important part of a protection system but just installing some in the antenna cable is not going to help so much. You need a system approach. If you do it right you can take a direct hit The big problem with grounding is Ohm's Law. That is if any current flows in a conductor that has resistance there will be a voltage across the conductor equal to the current times the resistance. But with lightening you can have 100,000 amps of current in a ground wire. If that wires has 0.01 ohms of resistance you have 1,000 volts above true ground on your ground connector on the lightening arrestor. Your ground is no longer at ground. You need some very tiny resistances and to get that you are going to need to do things like using multiple ground rods and large conductors. And connecting grounds together. On Thu, Oct 16, 2014 at 4:34 PM, Dave M dgmin...@mediacombb.net wrote: I'm looking for effective coaxial lightning arrestors for my GPSDO antennas. I've seen several types; those completely enclosed in a one-piece metal enclosure (no replaceable components) and those having a replaceable gas discharge tube seem to predominate the list. I'm looking closely at the gas discharge tube types, and am curious as to their effectiveness and durability. I'd like to know stuff like; are they effective in dissipating a static charge, how do I know when the gas tube needs to be replaced, are the gas tubes of a special type, are replacement gas tube easily available, etc. I'm interested in opinions and experiences with arrestors and recommendations for which type is most effective. Thanks for comments, Dave M ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. When the people fear the government, there is tyranny. When the government fears the people, there is liberty -- Thomas Jefferson Dave M ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Lightning arrestors for GPSDO antenna
On 10/16/14, 6:27 PM, Chris Albertson wrote: Lightening arrestors are an important part of a protection system but just installing some in the antenna cable is not going to help so much. You need a system approach. If you do it right you can take a direct hit The big problem with grounding is Ohm's Law. That is if any current flows in a conductor that has resistance there will be a voltage across the conductor equal to the current times the resistance. But with lightening you can have 100,000 amps of current in a ground wire. If that wires has 0.01 ohms of resistance you have 1,000 volts above true ground on your ground connector on the lightening arrestor. Your ground is no longer at ground. For lightning transients 1 us kind of rise times...inductance is a MUCH bigger deal than resistance, and inductance is very weakly dependent on conductors size and shape. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Lightning arrestors for GPSDO antenna
Years ago, I visited an installation that used a large triggered spark gap to discharge a large bank of caps at 100 KV into the primary of an air wound (about 8 feet in diameter) 1:10 step up pulse transformer connected to two aluminum plates about 30 feet square separated by several feet of water (the dielectric). At the center of the plates was a spark gap that was used to study EMP phenomena. There certainly was high power RF associated with the discharge, a tiny fraction of what a lightning bolt produces. All of the electronic measuring equipment was contained in a room-sized double-walled copper screen Faraday cage, so that the jumping lines on Tektronix 545 oscilloscopes didn't just show noise from the 100 KV gap firing. Even though grounding couldn't neutralize the effects of the pulse, the Faraday cage isolated the contents from the fields. The next best thing to a Faraday cage is a ground plane that has one connection to Earth ground. And if you can't get a great metal plate, a single point for all instrument grounds is the last best thing - if you have to have an elevated antenna. When I had a mast with two HP conical GPS antennas to a pair of HP Z3801A receivers, I chose a single Earth-grounded lightning rod for the plastic pipe mast. Nothing else connected to that ground. It was intended to discharge local induced static electricity, not take a direct hit. The equipment (and the antennas via the RG-8 cables) was all connected to a common ground point connected to the house electrical ground. The computer connections to the house network were wireless. No lightning arrestors were used. This system got one test when the neighbor took a direct hit to a tree close to his house. An arc jumped to a nearby outdoor floodlight and did considerable damage in his house. My antennas were about 100 feet away. The one nearest the strike died, but there were no other effects. Sadly, I was not motivated to examine the effect on the GPS receivers, although I still have the GPSCon data here somewhere. I gave the dead antenna to the man who bought my GPS setup (downsizing for the next stage of old age). He later told me that he fixed the antenna by replacing one of the amplifier chips. Sounds like EMP damage to me, the kind no arrestor could have helped. But I would not dissuade anyone from employing lightning arrestors, for the peace of mind it brings -- until a direct hit occurs. However, I'm in Minnesota with less than a tenth of the probability of a hit in, say, Florida. While there's not much about precision time in this posting, I hope it was useful to those who probe the sky with antennas. Bill Hawkins ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Lightning arrestors for GPSDO antenna
Of all device types, I think gas tubes are the best for this sort of application - very low C, and high surge current rating. I'm picturing the kind that are used in power supplies and such for limiting line transients - about 1 cm dia and length with axial leads. I don't know what kind are used in lightning arrestors, if they are the same or scaled up in size. Whether you make it able to take a direct hit depends on how big of a hit, your budget, and the environment of the antenna and lines. If it's the tallest thing in a huge field in a lightning-prone area, then it could be a big issue, but I don't think most people have that situation. You may want to look at the US National Electrical Code (NEC) for ideas - I believe that subject is covered there. The main thing there would be safety against injuries and fire, even if the equipment is destroyed. I think what you would want is kind of a pi network - the lowest impedance path to ground at the antenna zone that can be practically realized, then a high common-mode impedance (or even fusible) line to carry the signal to the building, then another low impedance path to ground at the building. This means that in my opinion, you should not put the feedline in metal conduit unless it's essential for protection - or underground, which should improve the grounding. You want the antenna zone to absorb the brunt of any discharge, then use the higher line Zcm to hopefully give some degree of isolation from there to the building. Ed ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
