Can I mount my Raymarine RS130 inside of a cockpit compartment or does it really need line of sight to the sky? Fiberglass is roughly 1/4" thick. Yes, I know what the manual says. Looking for opinions from those who've actually tried it
GPS receiver mounted below?
- Thread starter Project_Mayhem
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A couple (few?) decades ago I was putting Panasonic toughbooks in Fire department vehicles, internal gps antennae on the laptops worked fine in very thing Except trucks with aluminum diamond plate on the top of cab. My first gps was a tiny Garmin III with 1" screen that ran for years on the nav table because that was my only 12V outlet.
We have two GPS's under a 1.5" cored deck, one GPS inside a cabinet near the bilge (and that one is a Raymarine RS125 - the predecessor to your RS130), and a chartplotter with a built in GPS inside a fiberglass box underneath a 2" cored hardtop with metal frame and supports. All of them work perfectly.
Your phone gets a GPS signal in your basement and inside large buildings.
Mark
Your phone gets a GPS signal in your basement and inside large buildings.
Mark
That 1/4" of fiberglass is not an issue. That is the short answer. Remember, your less-capable GPS antenna on your phone works inside a car ... in the city.
The long answer:
At any given time, there are theoretically (and in practice) about 8-12 satellites visible on open water. You only actually need to see 3 to get a 2D fix, but you really want more like about 6 to get a good DOP (degree of precision).
So, in other words, you need to be able to see about half of the available satellites ... but ...
In practice, GPS signals are weak (received around –130 to –125 dBm), and satellites near the horizon are sketchy because:
If you imagine what your antenna can "see", looking at that useful dome, and you estimate that more than about 25% is blocked by metal or carbon fiber, then you might experience degraded performance. So, you wouldn't put it right under the mast or directly under a cleat, for example. But, in general, you don't have to put much thought into this. Just avoid the big stuff and stay away from small stuff within a foot or two.
The long answer:
- GPS satellites transmit at about 1.575 GHz (for L1 civilian band).
- Fiberglass largely transparent to radio waves at those frequencies.
- Metal: The larger the piece and the closer it is to the antenna, the greater the effect. Even small metal parts nearby (handrails, winches, frame tubes) can cause multipath errors (reflected signals confusing the GPS).
- Carbon fiber
- Dense wiring (if it is very near the antenna)
- Solar panels
- Obstructions below the antenna aren't really a problem. (In fact, a metal plate under the antenna, called a ground plane, can improve performance. Completely unnecessary, but interesting to know.)
- Obstructions horizontal to or above the antenna can interfere
- Smaller obstructions aren't much of an issue on a moving boat (because they only block/reflect the signal intermittently)
At any given time, there are theoretically (and in practice) about 8-12 satellites visible on open water. You only actually need to see 3 to get a 2D fix, but you really want more like about 6 to get a good DOP (degree of precision).
So, in other words, you need to be able to see about half of the available satellites ... but ...
In practice, GPS signals are weak (received around –130 to –125 dBm), and satellites near the horizon are sketchy because:
- The signal has to pass through more atmosphere (more attenuation and refraction),
- There is more multipath and those signals are subject to interference you can't control for.
If you imagine what your antenna can "see", looking at that useful dome, and you estimate that more than about 25% is blocked by metal or carbon fiber, then you might experience degraded performance. So, you wouldn't put it right under the mast or directly under a cleat, for example. But, in general, you don't have to put much thought into this. Just avoid the big stuff and stay away from small stuff within a foot or two.
Thanks everyone! I built a car computer. The GPS receiver had like four different states and had to warm up (ie find satellites) depending on how long it was off. The manual overwhelmingly stated that it needs clear views of the sky. Signals for phones have improved by leaps and bounds. I can now drive through downtown and on lower level streets without skipping a beat. 10 years ago? forget about it! I was better off writing down directions.
Another vote for being ok below decks... I have 3 GPS inside the cabin, although they are all 2020 + units.... yours being a 2010 ish unit, it should work? The receiver sensitivity has gotten better over the years (as the number of satellites tracked).... no harm in trying with a test setup.
Your phone's GPS works, inside a phone case, sometimes covered by the electronics/battery, inside a car, in a building / bus / train.....
Your phone's GPS works, inside a phone case, sometimes covered by the electronics/battery, inside a car, in a building / bus / train.....
And, that is technically true. It is just that many materials do not obstruct the view. And, this view doesn't have to be completley without obstructions.
Also, I think software/firmware has improved over the years to deal better with multipath, though I don't know that to be true - just an assumption.
Didn't they have those pesky things called maps, even back then?
I've always felt directions could be dangerous: if you missed a turn and went too far, you got lost. At least with a map you could work it out.
Yeah, but I wish Google Maps would say stuff like, "If you see a weird sign with a creepy smiling donut, you just missed it. Turn around at the 7-11 parking lot because you can't make a U-turn because they're doing road construction, then take the next left at the goat statue."Didn't they have those pesky things called maps, even back then?
It gets really confusing downtown Chicago on the lower levels. Add in people and cars darting in front of you, lack of or misleading streetsigns... I had to go to a service entrance to museum once. I pulled over after every turn to check the directions that were provided. I barely made it. The second time it took me three times to get it right. The guy that was working from me that day had just as many issuesDidn't they have those pesky things called maps, even back then?