[time-nuts] GPS Lightning Protection
edbriggs at outlook.com
Fri Oct 17 07:27:33 EDT 2014
The advice about a 'system approach' is essential, or the lightning discharge may go through your building wiring instead of through your ground rod. Or, a lightning strike down the street may follow the power line, pass through your home wiring, GPS receiver, and into your GPS antenna ground.
A nice overview of the basics of such a system approach for residential locations is presented in the IEEE Guide to Surge protection.
Since some time-nutters may be experimenting in residential settings, this guide may be more useful than guidance for industrial settings.
There are now approved ground bonding assemblies available for about $10 US dollars. (They're called 'Intersystem Bonding Termination' devices.). This can simplify the creation of a single ground point, and can help eliminate the clutter telephone and CATV grounding attachments to the electrical service ground. Get a licensed electrician to install it; don't modify your electrical service ground on your own.
Also, you mentioned something about connecting a copper wire to Aluminum. That may present problems or even be illegal in your area unless it is done correctly. In the U.S. you should check a recent edition of NFPA 780 and your local electrical code.
Also, if your home has lightning rods, these need to be included in the design.
Regarding gas discharge tubes, these are widely used, and they are often designed to fail 'shorted', so you can tell if they've failed by loss of signal. Replacement gas discharge tubes are available from the manufacturers.
The gas discharge units for GPS systems are designed to let the DC control voltage pass through ( usually 5 volts, some systems use 12 (eg some Symmetricom receivers)) and clamp any voltage higher that this. Note that the voltage referred to here is the difference between the shield and center conductor of the coax. You should look for an arrestor that handles the GPS frequency, and passes the DC voltage (non DC blocking) but limits surges to 6 or 15 volts (depending on your GPS supply voltage) , but not 300 or 600 volts that is common for suppressors designed for service with low power transmitters.
Some systems use two lightning arrestors, one at the antenna to protect it fromsurges appearing on the feedline, and one at the point of entry/single ground point.
Once you have a look at the IEEE guide, and the NFPA guide, you'll shudder when you read internet postings like : 'I just connected a lightning supressor to my radio and ran a wire to a 4 foot ground rod outside my window. It seems to be working fine'.
Best of Luck!
> > On Oct 16, 2014, at 7:34 PM, Dave M <dgminala at 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
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