Re: [time-nuts] lightening protection of a GPSDO system / optical isolated distribution amp
On 11/27/2014 01:10 AM, Jim Lux wrote: On 11/26/14, 2:54 PM, Hal Murray wrote: albertson.ch...@gmail.com said: The ground rod needs to be bonded to the rest of the building ground system. How do I do that effectively if the power goes in the front of the building and the antenna is on the back? AWG 6 wire with no breaks or splices between the two. The goal of bonding all the grounding systems together is not for transient suppression. It's to make sure that there's no DC or line frequency potential difference between electrical safety ground at various places in the building. The background on the whole grounding/bonding requirement is more about safety when a power carrying conductor, either inside equipment or overhead, touches something that people might touch. And, to a lesser extent to ensure that if there's an internal short, that the breaker or fuse will trip. NEC requirements for grounding and bonding aren't there for transient suppression. A copy of IEEE 1100 (the Emerald Book) is good reading for the whole bonding and equipotential planes, etc. (unfortunately not free from IEEE). A good book on transient protection is Ronald Standler's book protection of electronic circuits from overvoltages Something like $20 from Dover... Do use the ITU-T K-series as a reference, it's a great starting point and they are there for free download. The ITU-T K.27 explains grounding in a station, and that could be interesting food for though in many cases, where people try to motivate Isolated Bonding Network while Mesh Bonding Network might be better in the end. K.40 may be inspiring. K.97 a special case which is partly relevant here. Cheers, Magnus ___ 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] lightening protection of a GPSDO system / optical isolated distribution amp
Hi Ok, here’s the full and proper answer to the question. Anything less is simply not adequate: 1) Lay down some ground cables, say a few thousand of them. Run them out at least 1/4 mile in each direction from your structure. Make sure they are at least 00 gauge and buried 10 feet deep. 2) At the perimeter (20’ past the walls) of the structure put down an underground aluminum plate at least 1” thick. Extend it at least 10 feet under the structure. Bond all the ground cables to the plate. 3) Route all cables, wires, and pipes into and out of the structure to a single point below ground level. 4) Bond all cables, wires, and pipes to the plate at that single point and protect them to the plate with at least six properly rated protection devices in series. 5) Extend the plate up to enclose the structure. Make sure it does not touch the walls or roof at any point. Nothing from the structure should be outside the plate. There always should be a 10’ air gap. 6) Make sure that all joints in the plate are properly bonded to each other. Holes and openings are to be avoided. 7) If EMP from nuclear attack is a major concern, add about 3/8” of steel to the aluminum plate. Make sure all openings are fully covered in the event of nuclear attack. 8) Put up the usual towers at each corner of the plate, and 20’ beyond the edges of the plate. Independently ground each tower. Run cables between the towers to screen the top and sides of the plate. Tie the tower bases together with multiple 00 cables, all isolated from the ground cables in step 1. At all points above ground the cable / tower screen should have an air gap of 20’ to the plate. Congratulations .. you are now fully protected against lightning …. You can be sure that your basement timing system will be protected against disruption from lightning to the 99.99% ( 1 ppt ) level. None of your $150 GPS based timing boxes will be damaged. Should you properly and fully implement this system and have a problem from a lightning hit, I’ll personally replace any $150 box that is proven to be damaged by lightning with a similar box from my collection. I also will re-set your local clock against my wrist watch at no extra charge. This is about timing after all :) Yes, you can paint the structure any color the rest of the family finds pleasing. We would not want our *hobby* to impact them too much. Bob On Dec 7, 2014, at 7:39 AM, Magnus Danielson mag...@rubidium.dyndns.org wrote: On 11/27/2014 01:10 AM, Jim Lux wrote: On 11/26/14, 2:54 PM, Hal Murray wrote: albertson.ch...@gmail.com said: The ground rod needs to be bonded to the rest of the building ground system. How do I do that effectively if the power goes in the front of the building and the antenna is on the back? AWG 6 wire with no breaks or splices between the two. The goal of bonding all the grounding systems together is not for transient suppression. It's to make sure that there's no DC or line frequency potential difference between electrical safety ground at various places in the building. The background on the whole grounding/bonding requirement is more about safety when a power carrying conductor, either inside equipment or overhead, touches something that people might touch. And, to a lesser extent to ensure that if there's an internal short, that the breaker or fuse will trip. NEC requirements for grounding and bonding aren't there for transient suppression. A copy of IEEE 1100 (the Emerald Book) is good reading for the whole bonding and equipotential planes, etc. (unfortunately not free from IEEE). A good book on transient protection is Ronald Standler's book protection of electronic circuits from overvoltages Something like $20 from Dover... Do use the ITU-T K-series as a reference, it's a great starting point and they are there for free download. The ITU-T K.27 explains grounding in a station, and that could be interesting food for though in many cases, where people try to motivate Isolated Bonding Network while Mesh Bonding Network might be better in the end. K.40 may be inspiring. K.97 a special case which is partly relevant here. Cheers, Magnus ___ 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] lightening protection of a GPSDO system / optical isolated distribution amp
Bob, can you explain more about the effect of antenna performance on a GPSDO system? Now you have told me it is important, I would like to know more! My lab has an East facing window. Physically what is happening here is that the error bars on the fix your GPS gets will cycle over a 12 hour period because of the sats all have 12 hour orbital periods. If you can only see part of the sky the amplitude of this is greater. As an example thing of the worst possible case where you antenna can only see a few degrees of the sky. Every 12 hours one GPS satellite comes into view and your GPS gets a decent fix but then for 8 hours the GPS sees nothing and drifts off. Now think about moving the antenna to a marginally better place where it always sees at last ONE GPS stiletto but for 8 hours there are two and for 2hours there are three satellites. The quality if the fix would still vary but would be better. In the best case your 12 channel GPS receiver ALWAYS is able to select the 12 BEST places GPS satellites that are in view. This is not a great effect as long as there is enough sky that there are always some in view. Don t worry about listening strike on your antenna. If is FAR MORE likely that lighting will strike some utility pole within 1/4 mile of your house and the surge will come in through the AC mains power. So if you want to fix a problem fix that one first, then worry about less and less likely things. This is not to say not to take normal precautions and ground the iron pipe with a $7 aluminum ground wire just like you would do to an old fashioned TV antenna. -- 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] lightening protection of a GPSDO system / optical isolated distribution amp
Hi The 12 hour periodicity of GPS is (in general) less obvious in an ADEV plot than 24 and 48 hour effects. Part of this is due to the lower “floor” at longer tau. Another part of it is due to things like the ionosphere being at different places at the 12 hour points. Bob On Dec 7, 2014, at 2:27 PM, Chris Albertson albertson.ch...@gmail.com wrote: Bob, can you explain more about the effect of antenna performance on a GPSDO system? Now you have told me it is important, I would like to know more! My lab has an East facing window. Physically what is happening here is that the error bars on the fix your GPS gets will cycle over a 12 hour period because of the sats all have 12 hour orbital periods. If you can only see part of the sky the amplitude of this is greater. As an example thing of the worst possible case where you antenna can only see a few degrees of the sky. Every 12 hours one GPS satellite comes into view and your GPS gets a decent fix but then for 8 hours the GPS sees nothing and drifts off. Now think about moving the antenna to a marginally better place where it always sees at last ONE GPS stiletto but for 8 hours there are two and for 2hours there are three satellites. The quality if the fix would still vary but would be better. In the best case your 12 channel GPS receiver ALWAYS is able to select the 12 BEST places GPS satellites that are in view. This is not a great effect as long as there is enough sky that there are always some in view. Don t worry about listening strike on your antenna. If is FAR MORE likely that lighting will strike some utility pole within 1/4 mile of your house and the surge will come in through the AC mains power. So if you want to fix a problem fix that one first, then worry about less and less likely things. This is not to say not to take normal precautions and ground the iron pipe with a $7 aluminum ground wire just like you would do to an old fashioned TV antenna. -- 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. ___ 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] lightening protection of a GPSDO system / optical isolated distribution amp
The topic has shifted from lightning protection, but I thought I would share my experiences on diurnal timing shifts. On my home-built GPSDO, similar to the design posted by Lars Walenius some time ago, I can see variations in the TIC output that correlate well to to the variations 24 hours ago. The variations are about 100 ns p-p and are noticeably larger when it is raining outside. I think the variations were also greater over the summer, when the sky view was more obstructed by leaves. My system uses an Adafruit (Globaltop) GPS module, so not the greatest for timing applications. I have an outdoor puck antenna located a few feet above ground level and a few feet from a wooden house, with a mostly unobstructed view to the west. The time constant for steering the OCXO is set to 2048 sec. The timing variations appear as noisy lumps that last about 90 minutes, so the disciplining is reducing but not eliminating the variations. On Sun, Dec 7, 2014 at 2:49 PM, Bob Camp kb...@n1k.org wrote: Hi The 12 hour periodicity of GPS is (in general) less obvious in an ADEV plot than 24 and 48 hour effects. Part of this is due to the lower “floor” at longer tau. Another part of it is due to things like the ionosphere being at different places at the 12 hour points. Bob On Dec 7, 2014, at 2:27 PM, Chris Albertson albertson.ch...@gmail.com wrote: Bob, can you explain more about the effect of antenna performance on a GPSDO system? Now you have told me it is important, I would like to know more! My lab has an East facing window. Physically what is happening here is that the error bars on the fix your GPS gets will cycle over a 12 hour period because of the sats all have 12 hour orbital periods. If you can only see part of the sky the amplitude of this is greater. As an example thing of the worst possible case where you antenna can only see a few degrees of the sky. Every 12 hours one GPS satellite comes into view and your GPS gets a decent fix but then for 8 hours the GPS sees nothing and drifts off. Now think about moving the antenna to a marginally better place where it always sees at last ONE GPS stiletto but for 8 hours there are two and for 2hours there are three satellites. The quality if the fix would still vary but would be better. In the best case your 12 channel GPS receiver ALWAYS is able to select the 12 BEST places GPS satellites that are in view. This is not a great effect as long as there is enough sky that there are always some in view. -- --Jim Harman ___ 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] lightening protection of a GPSDO system / optical isolated distribution amp
Hi If you are happy with 1x10^ -9 frequency accuracy, then there are a number of things you can ignore. If you are after 1x10^-11 frequency accuracy 99.9% of the time you have to do everything right. Different limits apply to different measures of stability. To reduce multi path you need a clear sky view. To keep the timing solution in the GPS happy you need to let it see 80 % of the sats it should see. In this case stuff below 20 degrees does not count towards the total. In both cases the exact numeric impact depends on a bunch of things. It would take a few hundred pages to go into all of it. You ultimately need a site survey to work out the multi path math. In the extreme case the antenna can not see any sats. The math is simple then. Your stability is just that of your oscillator. That gets us right back to Rb's are better than OCXO's. Both are better than a TCXO. Best advice is still the same. Get as good a GPSDO as you can afford. Put the antenna up on the roof. Bob Sent from my iPhone On Nov 27, 2014, at 3:24 AM, Dr. David Kirkby (Kirkby Microwave Ltd) drkir...@kirkbymicrowave.co.uk wrote: On 27 Nov 2014 03:06, Bob Camp kb...@n1k.org wrote: Hi You need a good antenna setup to get a good disciplined oscillator. The bigger question is if you *need* the sort of “better” it gives you. If you are running a simple TCXO based GPSDO, you will have a number of issues to deal with compared to an OCXO or Rb based system. If “better” is an objective, consider the entire system. Bob Bob, can you explain more about the effect of antenna performance on a GPSDO system? Now you have told me it is important, I would like to know more! My lab has an East facing window. The only way I would use an external antenna is if I had optical isolation. I live in an area where the lightening risk is considered low, but having lost equipment twice, I am probably more concerned than others might be. Dave. ___ 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.
[time-nuts] lightening protection of a GPSDO system / optical isolated distribution amp
Said mentioned on an earlier thread that if a GPS antenna is used outside, lightening protection should be used. This immediately reminded me of something that happened about 10 years ago to me 1) Lightening damaged my ADSL modem. It because totally dead. 2) Every computer and a printer connected to that had the Ethernet ports blown up. After a hell of a fight with my insurance company, they paid up on my household insurance. The total cost was about £10,000, as all were Sun workstations, so a bit more expensive than a typical home computer. A few years after that, a similar thing happened, but just the ADSL modem got destroyed - no computers. Clearly if an external antenna is put in a high enough E-field or H-field, it can do damage to the antenna, and potentially anything connected to it, which would be all your test equipment, in much the same way all my computers got their Ethernet ports blown up. I would be *very* reluctant to use an external antenna, which is in some way connected to a distribution unit into the back of every bit of test equipment I have. I can see a potential (excuse the pun), of doing a serious amount of damage. The only way I would consider doing it, is if there was some optical isolation. In principle one could modulate a laser at 10 MHz, pass it down an optical fibre, then have a photodiode to recover the modulation. Can would obviously be needed not to compromise the signal, and that might be impossible. I realize the signal strength from an external antenna will be higher than an internal antenna, but does that make much (any?) difference to the operation of the GPSDO? FUNNY, SAD but TRUE story. After I got hit by lightening for the second time down my telephone line, I decided I needed to do something about it. So I got onto my service provider (BT) and asked them what could be done, as my telephone is fed via an overhead line. After arguing with them for months, they agree to fit some lightening protection to my telephone line. The day they came to fit this was a lesson in how incompetent some technicians, and their managers can be. Of course BT call them engineers, but this guy is not an engineering in my mind. BT TECHNICIAN: I need to run an earth wire ME: That is ok, so I assume you are going to put an earth rod into the ground. BT TECHNICIAN: No, I wont use an earth rod. ME: So how are you going to earth it? What sort of wire is it? BT TECHNICIAN: My manager said to move some earth away with my fingers, poke the wire into the ground, then move the earth back with my hand. The wire is 1 mm^2. ME: That is no good. Let me speak to your manager. The BT technician then rings his manager, and puts him on the phone. I explain that is not acceptable. MANAGER: So how do you suggest we earth it? ME: I don't know how to do it. This is not my area of expertise, but I know that what you are proposing, with 1 mm wire and poking the wire into the ground with your fingers is not acceptable. Dr. David Kirkby Ph.D CEng MIET Kirkby Microwave Ltd Registered office: Stokes Hall Lodge, Burnham Rd, Althorne, Essex, CM3 6DT, UK. Registered in England and Wales, company number 08914892. http://www.kirkbymicrowave.co.uk/ Tel: 07910 441670 / +44 7910 441670 (0900 to 2100 GMT only please) ___ 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] lightening protection of a GPSDO system / optical isolated distribution amp
The N2MO station has an external GPS antenna on the gable end of the building. It's connected to the polyphaser arrestor with FSJ4-50 superflex. The antenna mounting pipe has a #2 ground wire (33.6 mm/2) the polyphaser has it's own #2 ground wire. Both connect to an 8' x 5/8 (2.4m x 16mm) driven ground rod. The jacket of the superflex is grounded with the factoryt Andrew kit as well Even with the GPS antenna lower in elevation then the HF beam and other antenna (with similar protection) I have concerns about leaving it connected all the time. 73 Martin Flynn W2RWJ On 11/26/2014 4:37 PM, Dr. David Kirkby (Kirkby Microwave Ltd) wrote: Said mentioned on an earlier thread that if a GPS antenna is used outside, lightening protection should be used. This immediately reminded me of something that happened about 10 years ago to me (33.6 1) Lightening damaged my ADSL modem. It because totally dead. 2) Every computer and a printer connected to that had the Ethernet ports blown up. After a hell of a fight with my insurance company, they paid up on my household insurance. The total cost was about £10,000, as all were Sun workstations, so a bit more expensive than a typical home computer. A few years after that, a similar thing happened, but just the ADSL modem got destroyed - no computers. Clearly if an external antenna is put in a high enough E-field or H-field, it can do damage to the antenna, and potentially anything connected to it, which would be all your test equipment, in much the same way all my computers got their Ethernet ports blown up. I would be *very* reluctant to use an external antenna, which is in some way connected to a distribution unit into the back of every bit of test equipment I have. I can see a potential (excuse the pun), of doing a serious amount of damage. The only way I would consider doing it, is if there was some optical isolation. In principle one could modulate a laser at 10 MHz, pass it down an optical fibre, then have a photodiode to recover the modulation. Can would obviously be needed not to compromise the signal, and that might be impossible. I realize the signal strength from an external antenna will be higher than an internal antenna, but does that make much (any?) difference to the operation of the GPSDO? FUNNY, SAD but TRUE story. After I got hit by lightening for the second time down my telephone line, I decided I needed to do something about it. So I got onto my service provider (BT) and asked them what could be done, as my telephone is fed via an overhead line. After arguing with them for months, they agree to fit some lightening protection to my telephone line. The day they came to fit this was a lesson in how incompetent some technicians, and their managers can be. Of course BT call them engineers, but this guy is not an engineering in my mind. BT TECHNICIAN: I need to run an earth wire ME: That is ok, so I assume you are going to put an earth rod into the ground. BT TECHNICIAN: No, I wont use an earth rod. ME: So how are you going to earth it? What sort of wire is it? BT TECHNICIAN: My manager said to move some earth away with my fingers, poke the wire into the ground, then move the earth back with my hand. The wire is 1 mm^2. ME: That is no good. Let me speak to your manager. The BT technician then rings his manager, and puts him on the phone. I explain that is not acceptable. MANAGER: So how do you suggest we earth it? ME: I don't know how to do it. This is not my area of expertise, but I know that what you are proposing, with 1 mm wire and poking the wire into the ground with your fingers is not acceptable. Dr. David Kirkby Ph.D CEng MIET Kirkby Microwave Ltd Registered office: Stokes Hall Lodge, Burnham Rd, Althorne, Essex, CM3 6DT, UK. Registered in England and Wales, company number 08914892. http://www.kirkbymicrowave.co.uk/ Tel: 07910 441670 / +44 7910 441670 (0900 to 2100 GMT only please) ___ 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. - No virus found in this message. Checked by AVG - www.avg.com Version: 2014.0.4794 / Virus Database: 4189/8634 - Release Date: 11/26/14 -- V/Rbr Martin A. Flynnbr br Chief Technology Officerbr Information Age Learning Centerbr 2201 Marconi Roadbr Wall Township, NJ 07719br Cell: 732-585-9913br Email: a href=mailto:mar...@infoage.org;mar...@infoage.org/abr Visit us online at: a href=http://www.infoage.org;www.infoage.orgbr Likes us on a href=https://www.facebook.com/infoagesciencemuseum;Facebook!/abr br ___ 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] lightening protection of a GPSDO system / optical isolated distribution amp
On 11/26/14, 1:37 PM, Dr. David Kirkby (Kirkby Microwave Ltd) wrote: Said mentioned on an earlier thread that if a GPS antenna is used outside, lightening protection should be used. This immediately reminded me of something that happened about 10 years ago to me 1) Lightening damaged my ADSL modem. It because totally dead. 2) Every computer and a printer connected to that had the Ethernet ports blown up. Here's what we do at JPL for spaceflight equipment: reradiators. Antenna with preamp on the roof... long coax to wherever the signal is needed, amp(maybe), DC bias T (minicircuits has them, as do others, or build one), and a variable attenuator (in case the system has too much gain), feeding a passive antenna. Another passive antenna (or your GPS receiver or your whatever) is a meter or so away. The inside antennas can be pretty crude. I suspect stripping back 1/4 wavelength of coax shield would work. We use ones that resemble a hockey puck and that have the required bandwidth (L1,L2, L5). You could, if you like, build some sort of shielding box with absorber around the two antennas which would cut down on multipath reflections, etc. But that box would require some design so that it doesn't become the path for the lightning to your gear. The entire path from roof antenna to reradiator is sacrificial. The only way I would consider doing it, is if there was some optical isolation. In principle one could modulate a laser at 10 MHz, pass it down an optical fibre, then have a photodiode to recover the modulation. Can would obviously be needed not to compromise the signal, and that might be impossible. Sure, there's all sorts of RF over fiber stuff available. Some is even designed for GPS signals specifically. ___ 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] lightening protection of a GPSDO system / optical isolated distribution amp
On 11/26/14, 2:00 PM, Martin A Flynn wrote: The N2MO station has an external GPS antenna on the gable end of the building. It's connected to the polyphaser arrestor with FSJ4-50 superflex. The antenna mounting pipe has a #2 ground wire (33.6 mm/2) the polyphaser has it's own #2 ground wire. Both connect to an 8' x 5/8 (2.4m x 16mm) driven ground rod. The jacket of the superflex is grounded with the factoryt Andrew kit as well Even with the GPS antenna lower in elevation then the HF beam and other antenna (with similar protection) I have concerns about leaving it connected all the time. AWG #2 seems a tad overkill, the current in a stroke can be carried by AWG #10 without melting, but maybe you had a lot of it around for other reasons. I suspect the coax shield has smaller cross sectional area than AWG #2 and you'll protect your grounding wire by blowing up the coaxgrin. (in fact, looking at the data sheet for FSJ4-50, the DC resistance of the outer conductor is 1 ohm/1000 ft = AWG 10.. it's actually more resistance than the inner conductor (the inner conductor is 0.820ohms/kft, and 0.140 inch in diameter, compare to AWG 10 which is very close to 0.100 inch in diameter). Hopefully your driven ground rod is bonded to the other system grounds? I'd worry about multipath from the HF beam and tower (although maybe you're not using that GPS for time-nuts 1E-20 precision...grin) ___ 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] lightening protection of a GPSDO system / optical isolated distribution amp
You CAN (almost) lightening proof your system. The trick is to give lightening a low impedence path to grind at very opportunity. Start with the antenna mast and call. Use iron pipe for the mast and feed the antenna cable down the center of the pipe. Place two large ground clamps on this pipe and connect a large diameter wire that takes a straight path to a group rod.This will go a long way to diverting energy to ground because high voltage likes to flow on the outside of a conductor which would be the pipe and not so much the antenna cable. The ground rod needs to be bonded to the rest of the building ground system. Then the antenna cable passes through a metal bulkhead with a bulkhead connector and all this is also grounded. After this is might be a high voltage e on the center conductor. Use an lightening arrester that is bolted to the bulkhead. At this point you are reasonably safe. Remember that Ethernet is always gavalically isolated by transformers On Wed, Nov 26, 2014 at 1:37 PM, Dr. David Kirkby (Kirkby Microwave Ltd) drkir...@kirkbymicrowave.co.uk wrote: Said mentioned on an earlier thread that if a GPS antenna is used outside, lightening protection should be used. This immediately reminded me of something that happened about 10 years ago to me 1) Lightening damaged my ADSL modem. It because totally dead. 2) Every computer and a printer connected to that had the Ethernet ports blown up. After a hell of a fight with my insurance company, they paid up on my household insurance. The total cost was about £10,000, as all were Sun workstations, so a bit more expensive than a typical home computer. A few years after that, a similar thing happened, but just the ADSL modem got destroyed - no computers. Clearly if an external antenna is put in a high enough E-field or H-field, it can do damage to the antenna, and potentially anything connected to it, which would be all your test equipment, in much the same way all my computers got their Ethernet ports blown up. I would be *very* reluctant to use an external antenna, which is in some way connected to a distribution unit into the back of every bit of test equipment I have. I can see a potential (excuse the pun), of doing a serious amount of damage. The only way I would consider doing it, is if there was some optical isolation. In principle one could modulate a laser at 10 MHz, pass it down an optical fibre, then have a photodiode to recover the modulation. Can would obviously be needed not to compromise the signal, and that might be impossible. I realize the signal strength from an external antenna will be higher than an internal antenna, but does that make much (any?) difference to the operation of the GPSDO? FUNNY, SAD but TRUE story. After I got hit by lightening for the second time down my telephone line, I decided I needed to do something about it. So I got onto my service provider (BT) and asked them what could be done, as my telephone is fed via an overhead line. After arguing with them for months, they agree to fit some lightening protection to my telephone line. The day they came to fit this was a lesson in how incompetent some technicians, and their managers can be. Of course BT call them engineers, but this guy is not an engineering in my mind. BT TECHNICIAN: I need to run an earth wire ME: That is ok, so I assume you are going to put an earth rod into the ground. BT TECHNICIAN: No, I wont use an earth rod. ME: So how are you going to earth it? What sort of wire is it? BT TECHNICIAN: My manager said to move some earth away with my fingers, poke the wire into the ground, then move the earth back with my hand. The wire is 1 mm^2. ME: That is no good. Let me speak to your manager. The BT technician then rings his manager, and puts him on the phone. I explain that is not acceptable. MANAGER: So how do you suggest we earth it? ME: I don't know how to do it. This is not my area of expertise, but I know that what you are proposing, with 1 mm wire and poking the wire into the ground with your fingers is not acceptable. Dr. David Kirkby Ph.D CEng MIET Kirkby Microwave Ltd Registered office: Stokes Hall Lodge, Burnham Rd, Althorne, Essex, CM3 6DT, UK. Registered in England and Wales, company number 08914892. http://www.kirkbymicrowave.co.uk/ Tel: 07910 441670 / +44 7910 441670 (0900 to 2100 GMT only please) ___ 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] lightening protection of a GPSDO system / optical isolated distribution amp
albertson.ch...@gmail.com said: The ground rod needs to be bonded to the rest of the building ground system. How do I do that effectively if the power goes in the front of the building and the antenna is on the back? -- These are my opinions. I hate spam. ___ 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] lightening protection of a GPSDO system / optical isolated distribution amp
On 11/26/2014 5:14 PM, Jim Lux wrote: On 11/26/14, 2:00 PM, Martin A Flynn wrote: The N2MO station has an external GPS antenna on the gable end of the building. It's connected to the polyphaser arrestor with FSJ4-50 superflex. The antenna mounting pipe has a #2 ground wire (33.6 mm/2) the polyphaser has it's own #2 ground wire. Both connect to an 8' x 5/8 (2.4m x 16mm) driven ground rod. The jacket of the superflex is grounded with the factoryt Andrew kit as well Even with the GPS antenna lower in elevation then the HF beam and other antenna (with similar protection) I have concerns about leaving it connected all the time. AWG #2 seems a tad overkill, the current in a stroke can be carried by AWG #10 without melting, but maybe you had a lot of it around for other reasons. I suspect the coax shield has smaller cross sectional area than AWG #2 and you'll protect your grounding wire by blowing up the coaxgrin. (in fact, looking at the data sheet for FSJ4-50, the DC resistance of the outer conductor is 1 ohm/1000 ft = AWG 10.. it's actually more resistance than the inner conductor (the inner conductor is 0.820ohms/kft, and 0.140 inch in diameter, compare to AWG 10 which is very close to 0.100 inch in diameter). Hopefully your driven ground rod is bonded to the other system grounds? I'd worry about multipath from the HF beam and tower (although maybe you're not using that GPS for time-nuts 1E-20 precision...grin) The #2 copper was recycled. The main RF grounding trapeze is tied to the grounding electrode system with 1/0, which was also recycled from another project. Re the time-nuttery: Only 1E-14. Can't afford better (yet). ___ 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] lightening protection of a GPSDO system / optical isolated distribution amp
On 26 November 2014 at 22:14, Chris Albertson albertson.ch...@gmail.com wrote: You CAN (almost) lightening proof your system. BUT if the almost is not quite enough, one could damage a lot of expensive test kit. Remember that Ethernet is always gavalically isolated by transformers I lost Ethernet ports on * Sun Blade 2000 workstation * Sun Ultra 60 workstation * Sun Netra T1 server * HP Printer * ADSL modem All went at the same time. The next time just the modem went. But I think I will be using an internal antenna. Dave ___ 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] lightening protection of a GPSDO system / optical isolated distribution amp
On 11/26/2014 5:54 PM, Hal Murray wrote: albertson.ch...@gmail.com said: The ground rod needs to be bonded to the rest of the building ground system. How do I do that effectively if the power goes in the front of the building and the antenna is on the back? If cost is no object, a ring ground circling the building. Otherwise a bonding jumper between the electrical system ground and the antenna grounding connection, preferably staying outside the building. ___ 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] lightening protection of a GPSDO system / optical isolated distribution amp
Surround your house with a complete loop of #6 wire with 8-10 ft long ground rods every 10-12 ft (but no less than 6ft), bonded (clamped) to the ground at the service entrance. That's the simple answer. The somewhat longer answer is in a recent copy of the ARRL Handbook. Some will argue for smaller wire, etc, but those are just details. I am not an expert in this field. Bob - AE6RV From: Hal Murray hmur...@megapathdsl.net To: Discussion of precise time and frequency measurement time-nuts@febo.com Cc: hmur...@megapathdsl.net Sent: Wednesday, November 26, 2014 4:54 PM Subject: Re: [time-nuts] lightening protection of a GPSDO system / optical isolated distribution amp albertson.ch...@gmail.com said: The ground rod needs to be bonded to the rest of the building ground system. How do I do that effectively if the power goes in the front of the building and the antenna is on the back? -- These are my opinions. I hate spam. ___ 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] lightening protection of a GPSDO system / optical isolated distribution amp
On 11/26/14, 2:14 PM, Chris Albertson wrote: You CAN (almost) lightening proof your system. The trick is to give lightening a low impedence path to grind at very opportunity. Start with the antenna mast and call. Use iron pipe for the mast and feed the antenna cable down the center of the pipe. Place two large ground clamps on this pipe and connect a large diameter wire that takes a straight path to a group rod.This will go a long way to diverting energy to ground because high voltage likes to flow on the outside of a conductor which would be the pipe and not so much the antenna cable. Not so much high voltage, as AC and skin effect. However, bear in mind that lightning has a rise time of a microsecond or so: you can think of it having a fundamental of 300-500 kHz (e.g. the first quarter cycle of a sinewave), with most of the power below 1MHz. Skin depth at 1 MHz in copper is 0.065mm. In iron (using conductivty of 9.6 and relative mu of 1000) skin depth is 0.005 mm So, steel/iron pipe is a terrible conductor for a lightning impulse, compared to that nice copper coax next to it, or inside it. The ground rod needs to be bonded to the rest of the building ground system. Then the antenna cable passes through a metal bulkhead with a bulkhead connector and all this is also grounded. After this is might be a high voltage e on the center conductor. Use an lightening arrester that is bolted to the bulkhead. From a electrical code standpoint, a grounded bulkhead connector isn't compliant: you need one of those clamps that attaches to the shield in a quasi permanent way. I'm not sure of the entire rationale, but I think it's because connectors can become disconnected, but bolted connections less so. At this point you are reasonably safe. Remember that Ethernet is always gavalically isolated by transformers Which won't necessarily stand off a 10 kV lightning impulse. and, of course, a common mode impulse carried on both wires of a pair might couple via either capacitance, or more likely, through magnetic fields. the ethernet galvanic isolation does a nice job dealing with the 10s or maybe 100V common mode issues, and protects the network if there is an internal short in a piece of equipment connected to the network. Of course, with the increased prevalence of Power Over Ethernet, some implementations of which are, shall we say, sketchy, that PoE system might be a dandy conductor of transient energy. For instance, a point to point microwave network terminal up on a mast running power for the circuit up the network cable. ___ 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] lightening protection of a GPSDO system / optical isolated distribution amp
On 11/26/14, 2:54 PM, Hal Murray wrote: albertson.ch...@gmail.com said: The ground rod needs to be bonded to the rest of the building ground system. How do I do that effectively if the power goes in the front of the building and the antenna is on the back? AWG 6 wire with no breaks or splices between the two. The goal of bonding all the grounding systems together is not for transient suppression. It's to make sure that there's no DC or line frequency potential difference between electrical safety ground at various places in the building. The background on the whole grounding/bonding requirement is more about safety when a power carrying conductor, either inside equipment or overhead, touches something that people might touch. And, to a lesser extent to ensure that if there's an internal short, that the breaker or fuse will trip. NEC requirements for grounding and bonding aren't there for transient suppression. A copy of IEEE 1100 (the Emerald Book) is good reading for the whole bonding and equipotential planes, etc. (unfortunately not free from IEEE). A good book on transient protection is Ronald Standler's book protection of electronic circuits from overvoltages Something like $20 from Dover... ___ 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] lightening protection of a GPSDO system / optical isolated distribution amp
Here is a link to a good 12 page description of grounding practices/requirements. http://www.reeve.com/Documents/Articles%20Papers/AntennaSystemGroundingRequirements_Reeve.pdf ___ 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] lightening protection of a GPSDO system / optical isolated distribution amp
You really do have to bond the two of them. The VERY best way is to dig a trench all the way around the building and install a loop of wire, #8 at least (although I use much larger wire after the time and money to dug a trench.) This wire connects the rods and the water system. While a full loop is best yo can simply run a wire to the building's service entrance but I think code requires these wires to be protected by any of several methods. You have to connect the grounds because otherwire you have a problem where indoors there are two different ground potentials. The Earth is just that way, there is or may be a voltage potential between two spots. There WILL be a difference during a lightening strike. On Wed, Nov 26, 2014 at 2:54 PM, Hal Murray hmur...@megapathdsl.net wrote: albertson.ch...@gmail.com said: The ground rod needs to be bonded to the rest of the building ground system. How do I do that effectively if the power goes in the front of the building and the antenna is on the back? -- These are my opinions. I hate spam. ___ 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] lightening protection of a GPSDO system / optical isolated distribution amp
On 27 Nov 2014 01:14, Chris Albertson albertson.ch...@gmail.com wrote: After this minimum you have th think about the probability of a strike. If you live in Orlando Florida then it might be 100% and nearly zero in other places and then you ask what the radio equipment cost. I paid $18 for my Motorola Encore GPS receiver. Chris, if a GPS receiver was the only item that would get damaged I would not care. If it damaged 3 signal generators, three VNAs, a frequency counter, and a spectrum analyzer, I would care. My experience with the lighting going down the telephone line and destroying a few computers, printer and modem would make me unhappy about an external antenna. Nobody has answered my other question - whether one gets a better disciplined oscillator with an external antenna. Dave. ___ 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] lightening protection of a GPSDO system / optical isolated distribution amp
On 11/26/14, 5:23 PM, Chris Albertson wrote: On Wed, Nov 26, 2014 at 4:03 PM, Jim Lux jim...@earthlink.net wrote: On 11/26/14, 2:14 PM, Chris Albertson wrote: You CAN (almost) lightening proof your system. The trick is to give lightening a low impedence path to grind at very opportunity. Start with the antenna mast and call. Use iron pipe for the mast and feed the antenna cable down the center of the pipe. Place two large ground clamps on this pipe and connect a large diameter wire that takes a straight path to a group rod.This will go a long way to diverting energy to ground because high voltage likes to flow on the outside of a conductor which would be the pipe and not so much the antenna cable. Not so much high voltage, as AC and skin effect. However, bear in mind that lightning has a rise time of a microsecond or so: you can think of it having a fundamental of 300-500 kHz (e.g. the first quarter cycle of a sinewave), with most of the power below 1MHz. Skin depth at 1 MHz in copper is 0.065mm. In iron (using conductivty of 9.6 and relative mu of 1000) skin depth is 0.005 mm So, steel/iron pipe is a terrible conductor for a lightning impulse, compared to that nice copper coax next to it, or inside it. Really? What you care about is the impedance, not the depth of the skin effect. Also not the the coax is NOT exposed to the environment. Tacitly the coax comes out from the user side of the antenna, so it never sees daylight. The current flows in that first .005mm of steel. Running the coax down the side of the pipe would be a really bad idea. Skin effect greatly affects the resistive impedance. Compare a copper pipe vs a steel pipe of the same diameter. The copper is basically conductive ring 0.065 mm thick and resistivity of 1.67 and the steel is .005mm thick and resistivity 9.6 So the resistance ratio is 26:1920.. that is 2 orders of magnitude. However.. the dominant impedance at lightning frequencies (at least for copper) is the inductance, which is very weakly dependent on the shape and cross-sectional size of the conductor: it's close to 1 uH/meter regardless.. A copper pipe that is 2 cm in diameter and 1 meter long has a resistance at 1 MHz of 0.004 Ohm A steel/iron pipe that is 2 cm in diameter and 1 meter long has a resistance at 1 MHz of 1.43 Ohm The inductive impedance is about 6.3 ohms. So the steel has a somewhat higher impedance than the coax inside it. Yeah, there probably is some shielding effect, but I'm going to guess that there's some insulating gap between the bottom of antenna and top of pipe, although that gap may be bridged by the plasma from your lightning strike. It's just that I'm not sure I'd trust the shielding effect of the pipe, nor any preferential current distribution from the magnetic fields. For all one knows, that pipe might wind up filled with a plasma of vaporized coax. I'd just consider the antenna and feedline sacrificial, and worry about dealing with the transient at the point of entry to the building, assuming that the coax is carrying all of it. ___ 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] lightening protection of a GPSDO system / optical isolated distribution amp
Sweet. I settled on #3 copper for my antenna grounding system on economic grounds and had a debate with a residential electrical contractor about bonding the antenna ground to the electrical service ground. The city inspector passed the system with the bond installed. I haven't used poly phasers but do hope to at least stop the house from burning down in the event of a lightning strike on the roof mounted antennas. I also found that the metallic city water supply pipe is by far the best ground I have (at least for 60 cycle AC.) (Using a clamp on meter I can measure an appreciable current thru it, unlike the other two grounds. I presume the current is being diverted from the utility neutral and is eventually making it's way back to the transformer that powers my house.) I'm glad the water pipe is also bonded to the electrical service ground. I'm happy that I don't have any appreciable currents flowing thru my antenna ground.This might be something to carefully consider (or possibly have looked at by a pro) if you have a really low impedance ground. I've heard anecdotal accounts of sparks occurring when low impedance antenna grounds are connected to an electrical service ground. My usual disclaimer of I'm not an expert in this field, the preceding is only my opinion, and don't rely on this applies. Mark Spencer On 2014-11-26, at 2:56 PM, Martin A Flynn mafl...@theflynn.org wrote: On 11/26/2014 5:14 PM, Jim Lux wrote: On 11/26/14, 2:00 PM, Martin A Flynn wrote: The N2MO station has an external GPS antenna on the gable end of the building. It's connected to the polyphaser arrestor with FSJ4-50 superflex. The antenna mounting pipe has a #2 ground wire (33.6 mm/2) the polyphaser has it's own #2 ground wire. Both connect to an 8' x 5/8 (2.4m x 16mm) driven ground rod. The jacket of the superflex is grounded with the factoryt Andrew kit as well Even with the GPS antenna lower in elevation then the HF beam and other antenna (with similar protection) I have concerns about leaving it connected all the time. AWG #2 seems a tad overkill, the current in a stroke can be carried by AWG #10 without melting, but maybe you had a lot of it around for other reasons. I suspect the coax shield has smaller cross sectional area than AWG #2 and you'll protect your grounding wire by blowing up the coaxgrin. (in fact, looking at the data sheet for FSJ4-50, the DC resistance of the outer conductor is 1 ohm/1000 ft = AWG 10.. it's actually more resistance than the inner conductor (the inner conductor is 0.820ohms/kft, and 0.140 inch in diameter, compare to AWG 10 which is very close to 0.100 inch in diameter). Hopefully your driven ground rod is bonded to the other system grounds? I'd worry about multipath from the HF beam and tower (although maybe you're not using that GPS for time-nuts 1E-20 precision...grin) The #2 copper was recycled. The main RF grounding trapeze is tied to the grounding electrode system with 1/0, which was also recycled from another project. Re the time-nuttery: Only 1E-14. Can't afford better (yet). ___ 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] lightening protection of a GPSDO system / optical isolated distribution amp
In my opinion, I'd be inclined to find a way to run a suitable wire around the building.I don't think you want your interior electrical wiring serving as the only bond between two different grounds if energy from a lightning strike flows thru your antenna feed line and then thru your time nuts gear that probably has a path to the other ground thru the wiring in the building. Other fault conditions that cause significant currents to flow thru your ground system could also cause issues if the only bond between the two ground systems is thru your house wiring and time nuts gear. Disclaimer I'm not an electrical engineer or lightning protection expert so please don't rely on this comment. Mark Spencer On 2014-11-26, at 2:54 PM, Hal Murray hmur...@megapathdsl.net wrote: albertson.ch...@gmail.com said: The ground rod needs to be bonded to the rest of the building ground system. How do I do that effectively if the power goes in the front of the building and the antenna is on the back? -- These are my opinions. I hate spam. ___ 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] lightening protection of a GPSDO system / optical isolated distribution amp
Hi You need a good antenna setup to get a good disciplined oscillator. The bigger question is if you *need* the sort of “better” it gives you. If you are running a simple TCXO based GPSDO, you will have a number of issues to deal with compared to an OCXO or Rb based system. If “better” is an objective, consider the entire system. Bob On Nov 26, 2014, at 7:30 PM, Dr. David Kirkby (Kirkby Microwave Ltd) drkir...@kirkbymicrowave.co.uk wrote: On 27 Nov 2014 01:14, Chris Albertson albertson.ch...@gmail.com wrote: After this minimum you have th think about the probability of a strike. If you live in Orlando Florida then it might be 100% and nearly zero in other places and then you ask what the radio equipment cost. I paid $18 for my Motorola Encore GPS receiver. Chris, if a GPS receiver was the only item that would get damaged I would not care. If it damaged 3 signal generators, three VNAs, a frequency counter, and a spectrum analyzer, I would care. My experience with the lighting going down the telephone line and destroying a few computers, printer and modem would make me unhappy about an external antenna. Nobody has answered my other question - whether one gets a better disciplined oscillator with an external antenna. Dave. ___ 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.
