GPS antenna under clay tile roof? - Page 1
Forum section: electronics / beginners

author: FriedMule
author_rank: Frequent Contributor
timestamp: June 09, 2020, 11:58:57 pm
content: I am about to decide where to mount a GPS antenna for a frequency standard, it can use up to 16 satellites at once.If I do get permission and get an electrician to perform the installation, I can get the antenna outside, and I am ready to chose that solution., but is that necessary?I have tile roof and is thinking if the GPS antenna could be mounted inside, just a few inches from the tiles. The tiles are made of clay.

author: ArthurDent
author_rank: Super Contributor
timestamp: June 10, 2020, 12:16:18 am
content: That doesn't look like the standard GPS amplified antenna where the +5 VDC power is supplied to the antenna by the receiver on the same coax that sends the signal to the receiver. What you have seems to have 4 insulated leads that I've seen on some antennas that have the entire receiver built into the antenna housing and have + and - power and receive and transmit for RS-232. You can't use this for timing purposes, only location when connected to a computer with a GPS program. Here's a photo of one with the same color code on the wires.

author: FriedMule
author_rank: Frequent Contributor
timestamp: June 10, 2020, 12:57:10 am
content: Sorry, the picture did I choose to show how the antenna-part looks like, my antenna can be screwed directly to the frequency standard and did function fine when I let it be outside.

author: JustMeHere
author_rank: Frequent Contributor
timestamp: June 10, 2020, 01:37:13 am
content: GPS is not a big fan of changes in density. It uses time delays to calculate position. So even a cloud can cause you to move although you're standing still. Reflections off of mountains and buildings can cause problems too.

author: FriedMule
author_rank: Frequent Contributor
timestamp: June 10, 2020, 01:46:13 am
content: hmm okay. Do and frequency standard with GPS, also account for location?Is there a way to test it myself?

author: wizard69
author_rank: Super Contributor
timestamp: June 10, 2020, 03:57:57 pm
content: It is doubtful the receiver will work under a clay roof. However you can test this easily by plugging in and seeing what happens.As for a electrician if this is all low voltage wiring you may not need a licensed electrician to install it. It depends upon your local regulations.

author: Cerebus
author_rank: Super Contributor
timestamp: June 10, 2020, 04:29:03 pm
content: Quote from: wizard69 on June 10, 2020, 03:57:57 pmIt's low voltage right up to the moment it becomes a high voltage, low impedance source during a lightning strike. If a GPS antenna is mounted where it wants to be (with a 360º view of the horizon) it's going to be the highest point on the building and hence a 'magnet' for lightning strikes.Whatever your local planning or building regulations it's a good idea to consider what is going to happen if you get a lightning strike on your GPS antenna and how you're going to protect yourself and your equipment from the consequences. The risks are no more, and no less, than any other kind of building mounted antenna, but people tend to just blithely forget that it could (very briefly) become the focus of lots of volts and thousands of amps. Many professional GPS antenna kits have optionallightning arrestorsincluded, if you haven't got one with yours it is the least you should think about adding to your setup if you're mounting the antenna outdoors.I've operated a GPS antenna successfully under a slate roof but it was much more likely to drop out and not be able to see any usable satellites in comparison to an antenna just casually hung out of the window. It'll work, but it won't work well. Just as crucial as what material is in the way, is what view of the horizon the antenna has. If you can get some height, and get above your own building and other buildings around you will get a much more reliable set up because you have more chance of seeing more satellites simultaneously and so giving your receiver more to work with.Oh, andbeware of door-to-door lightning rod salesmen.

author: jpb
author_rank: Super Contributor
timestamp: June 10, 2020, 05:06:25 pm
content: When I was setting up my antenna I thought of doing this, and as an experiment I went round with a gps puck antenna/receiver and a laptop to take measurements. (I went round the garden and up into the loft.)I seem to remember that there was about a 10dB drop through my tiled roof (probably concrete tiles rather than clay - they're fake clay).This is probably ok if going from 50 dB down to 40dB.In the end I put it on my garden fence. It doesn't see that many satellites but gets good reception from those it sees and for timing (rather than navigation) you don't need a lot of satellites.I do have a lightening arrester wired to a ground rod put into the ground for the purpose (not my main house earth) but I'm not sure how effective it would be for a direct hit but I'm not worried as the house has a tv aerial high on the roof and in 30 years has never been hit. There are also a lot of tall trees around about so I think my top-of-fence gps antenna is very unlikely to be the thing that is hit.

author: wizard69
author_rank: Super Contributor
timestamp: June 11, 2020, 04:02:21 am
content: Unless that electrician has had training in lightening arresting systems he will know little about that field. You could certainly look for an electrician that knows NFPA 780 well.The bigger problem is that good practice is no guarantee with respect to lightning. Energy level very but I've had co workers that have had a whole chimneys blown off their house. Some times a ground cable isn't enough.Quote from: Cerebus on June 10, 2020, 04:29:03 pmWhile a high point is a factor it has to be high enough to clear all other roof projections. That included plumbing vents, furnace and hot water heater stacks.and whatever else is projecting above the roof. This little antenna isn't that high and frankly can be positioned for an absolute minimal projection. This isn't like the big VHF TV antennas that where popular in the past most of which came with lightening control instructions or advice.QuoteI have to disagree here. The vast majority of lightning damage to equipment does not come from a direct strike. It i more about the step change in the local electrical field impressing a big voltage potential on large antenna arrays. Large antennas pick out that impulse and that is what blows out a lot of TV's and equipment connected to the TV. It is very easy to see this in people that have suffered near by lightening strikes and have loss electronics in the house. Of course a lightening arrestor might prevent this or it might not.QuoteThis is the point I was trying to get at, the real answer is for the guy to check for himself how badly the roof attenuates the signal. The only thing I can say is that it generally a bad idea.

author: FriedMule
author_rank: Frequent Contributor
timestamp: June 11, 2020, 06:31:49 am
content: You are all great and seems to agree upon that an antenna inside is safer but also generally a les optimal idea if I want to be sure I always have a signal.About the antenna and lightning. Please know that I have about no idea on what I am talking about and all the following is based on my guess.The antenna is 4 inch in diameter and about 5 inch in height, so not the biggest antenna. I have an idea that the chance of a lightning strike, hitting the antenna will be greater if I add an easy way for the lightning to go to the ground, and since the antenna is so tiny, it's will rater hit something else, like my 12 high inch air went.I do plan on placing the antenna as low as possible, so the antenna can "look" at the sky but maybe still be below the roof top.The reason for using a professional is for tree reasons, first do hi take the responsibility for the installation been done correct, second do my landlord demand that every installation is performed by an expert, third do I fear height and have no wish on walking around outside on the roof:-)In the area around my house is there a lof of other buildings in the same height, some trees that are higher then my building, and about 200 feet from my house are there a high building with lightning protection.Based on that, would you think it's safe enough or will you still recommend an ground connection at my antenna?

author: Cerebus
author_rank: Super Contributor
timestamp: June 11, 2020, 02:08:45 pm
content: Quote from: wizard69 on June 11, 2020, 04:02:21 amGood luck with finding a Danish antenna installer that knows an American National Standard.EN 62305 might be more appropriate.

author: FriedMule
author_rank: Frequent Contributor
timestamp: June 11, 2020, 03:23:14 pm
content: LOL yes:-)Did just not to correct the standard, sins it was a great advice, just the wrong standard.

author: SeanB
author_rank: Super Contributor
timestamp: April 26, 2021, 07:33:46 pm
content: I have had good results running a small puck GPS with it just sitting on the window sill inside the room, with the glass pane there. Northwest facing window, and after around 20 minutes it was giving valid data, which was reasonably stable as well, so just try the window first, provided it is not a metallised glass type. Worth just trying this first, and then see how stable the unit is after it has acquired a few fixes.

author: Gyro
author_rank: Super Contributor
timestamp: April 26, 2021, 08:08:42 pm
content: Just to add a 'vote' to the mix. I've successfully a operated Puck antenna on a metal ground plane, in the loft under a tiled roof. It is certainly more convenient than having to worry about waterproofing and lightning protection.I also have a decent sized UHF TV antenna and amplifier mounted in the loft for similar convenience reasons.