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Should work under bimini
RF signals at frequency and the strength typically received from gps satellites are not degraded by travelling through fabric. If I had to guess, I'd bet Gregg's problem is due to proximity with the bows rather than the bimini material. As long as the gps antenna "view" is unrestricted by metal, it should work fine
RF signals at frequency and the strength typically received from gps satellites are not degraded by travelling through fabric. If I had to guess, I'd bet Gregg's problem is due to proximity with the bows rather than the bimini material. As long as the gps antenna "view" is unrestricted by metal, it should work fine
Mine works under the canvas
But before you try moving the antenna, try folding the bimini and see if it works any better. I suspect some other problem.
But before you try moving the antenna, try folding the bimini and see if it works any better. I suspect some other problem.
Bimini likely not the problem
My GPS antenna is mounted inside one of my engine rooms and is very content "seeing" through fiberglass. My handheld units can see through the cabin roof from the chart table. Dave S/V Pas de Deux Catana 471-44
My GPS antenna is mounted inside one of my engine rooms and is very content "seeing" through fiberglass. My handheld units can see through the cabin roof from the chart table. Dave S/V Pas de Deux Catana 471-44
GPS working frequencies
1.5 and 1.2 GHz which makes the wave length of around 2 centimeters or about an inch. This is slightly longer (passes through stuff "better") than your cordless phone which operates at 2.4 GHz. This wave length will pass through most common household stuff like walls and such. It does have problems with metal that is close to its wave length in size. Your Bimini frame, stern rail, and helm wheel come to mind. All these things act like little antennas and cause lots of signal attenuation. Your Bimini top is certainly not the problem but the exact placement of the GPS antenna inside this rather complex antenna field (all the metal stuff) is certainly going to be problematic at best. There are going to be dead spots in the cockpit and under the dodger. Your best bet is to get the antenna outside the interference by placing it above the bimini by at least a few inches. Try not to mount it on a bimini frame member. Also remember that the satellites move around so what works now may not work in 15 minutes. If you really want to get geeky you could turn on the "satellites" page of the GPS and start noting where the satellites are in the sky and which ones are getting good and which are getting poor reception. Note their positions relative to the cockpit and see if there is one part of the "cockpit sky" that when they enter it you loose their signal. Note: this will take quite a while so you might want to plan to have something else to do while you wait.
1.5 and 1.2 GHz which makes the wave length of around 2 centimeters or about an inch. This is slightly longer (passes through stuff "better") than your cordless phone which operates at 2.4 GHz. This wave length will pass through most common household stuff like walls and such. It does have problems with metal that is close to its wave length in size. Your Bimini frame, stern rail, and helm wheel come to mind. All these things act like little antennas and cause lots of signal attenuation. Your Bimini top is certainly not the problem but the exact placement of the GPS antenna inside this rather complex antenna field (all the metal stuff) is certainly going to be problematic at best. There are going to be dead spots in the cockpit and under the dodger. Your best bet is to get the antenna outside the interference by placing it above the bimini by at least a few inches. Try not to mount it on a bimini frame member. Also remember that the satellites move around so what works now may not work in 15 minutes. If you really want to get geeky you could turn on the "satellites" page of the GPS and start noting where the satellites are in the sky and which ones are getting good and which are getting poor reception. Note their positions relative to the cockpit and see if there is one part of the "cockpit sky" that when they enter it you loose their signal. Note: this will take quite a while so you might want to plan to have something else to do while you wait.
I Have Heard...
...that a wet bimini top will affect (block) GPS signals. In my experience with my GPS Chartplotter for the last 5 years, I have had no issues, even in a heavy rain with the Bimini top mounted.
...that a wet bimini top will affect (block) GPS signals. In my experience with my GPS Chartplotter for the last 5 years, I have had no issues, even in a heavy rain with the Bimini top mounted.
er, Bill, about the freq 7 wavelength
Bill, You are correct, mostly. But as frequency goes UP, wavelength goes DOWN. So, your model of 1.2ghz for gps vs. 2.4 for cordless phones would mean that the wavelength for cordless phones is half that of the gps. Formula is wavelength = 300 divided by frequency in MHz. Now the formula for us earthbounders is frequency in MHz divided into 468, which will give you the wavelength in feet for a half wave length dipole.
Bill, You are correct, mostly. But as frequency goes UP, wavelength goes DOWN. So, your model of 1.2ghz for gps vs. 2.4 for cordless phones would mean that the wavelength for cordless phones is half that of the gps. Formula is wavelength = 300 divided by frequency in MHz. Now the formula for us earthbounders is frequency in MHz divided into 468, which will give you the wavelength in feet for a half wave length dipole.
The higher the frequency...
The more susceptible to rain fade or rain attenuation. GPS works in the L-band frequency range (950MHz to 1450 MHz or as high as 1700MHz). This frequency range is not as susceptible to rain fade as C-band (3 to 8 GHz) and K-band (12 to 40 GHz). Think about how a microwave oven works. It's frequency range is around 2.4 GHz and has a very high powered amplifier. It heats up food by bombarding the moisture in the food. If there is no moisture, then there is no heat generated. Satellite systems work the same way, except the radiated signal is so week that it is readily absorbed by the moisture in the air. More moisture, like rain and snow, will cause a signal to just... vanish. So, GPS signals, as indicated, can penetrate any media that does not contain extensive moisture or has a dense metallic core. Is is very common to install a satellite dish in a fiberglass enclosure. You see these on cruise ships and larger yachts all the time. I would agree with Bill Roosa in principle, but I think the cause of a loss of signal is more attuned to shadowing (objects blocking the view of the satellite) rather that near field absorption. But in GPS, there are so many visible (and it only takes two birds to plot, preferably 3 for three dimensional ploting) satellites that I doubt the problem is shadowing. My .02
The more susceptible to rain fade or rain attenuation. GPS works in the L-band frequency range (950MHz to 1450 MHz or as high as 1700MHz). This frequency range is not as susceptible to rain fade as C-band (3 to 8 GHz) and K-band (12 to 40 GHz). Think about how a microwave oven works. It's frequency range is around 2.4 GHz and has a very high powered amplifier. It heats up food by bombarding the moisture in the food. If there is no moisture, then there is no heat generated. Satellite systems work the same way, except the radiated signal is so week that it is readily absorbed by the moisture in the air. More moisture, like rain and snow, will cause a signal to just... vanish. So, GPS signals, as indicated, can penetrate any media that does not contain extensive moisture or has a dense metallic core. Is is very common to install a satellite dish in a fiberglass enclosure. You see these on cruise ships and larger yachts all the time. I would agree with Bill Roosa in principle, but I think the cause of a loss of signal is more attuned to shadowing (objects blocking the view of the satellite) rather that near field absorption. But in GPS, there are so many visible (and it only takes two birds to plot, preferably 3 for three dimensional ploting) satellites that I doubt the problem is shadowing. My .02
Joe and Brian
Joe I think that is what I said. A longer wavelength will pass through more "stuff" than a shorter wavelength. A good example is an 8 Hz wave will pass quite easily through the entire earth. When you get down to the wave length being less than a centimeter you are not going to get it to pass through much and when you get to mm wavelengths you get the wave attenuated by just about everything and down to nanometers and visible light it can't even pass through a piece of paper. So longer wavelengths pass through things better than shorter ones (provided they are not metal things). Brian What is the difference between near field absorption and shadowing besides one being a technical term for the other?
Joe I think that is what I said. A longer wavelength will pass through more "stuff" than a shorter wavelength. A good example is an 8 Hz wave will pass quite easily through the entire earth. When you get down to the wave length being less than a centimeter you are not going to get it to pass through much and when you get to mm wavelengths you get the wave attenuated by just about everything and down to nanometers and visible light it can't even pass through a piece of paper. So longer wavelengths pass through things better than shorter ones (provided they are not metal things). Brian What is the difference between near field absorption and shadowing besides one being a technical term for the other?
A Faraday Shield...
Would be used to absorb energy but requires several tuned elements in the both electrical and magnetic fields. I could see near field absorption causing an adverse effect, but not so much on a boat, except in the case of moisture absorption. Blocking is a form of absorption, but it does not have to be electrical or magnetic in nature. It could have a scattering or reflective effect in which the antenna would then receive two signals of different polarity thus canceling each other out. In the case of the GPS antenna being in this field, then it is very possible that reflective signals are causing the GPS receiver to not acquire. This is where I agree with your analysis. My .02, again.
Would be used to absorb energy but requires several tuned elements in the both electrical and magnetic fields. I could see near field absorption causing an adverse effect, but not so much on a boat, except in the case of moisture absorption. Blocking is a form of absorption, but it does not have to be electrical or magnetic in nature. It could have a scattering or reflective effect in which the antenna would then receive two signals of different polarity thus canceling each other out. In the case of the GPS antenna being in this field, then it is very possible that reflective signals are causing the GPS receiver to not acquire. This is where I agree with your analysis. My .02, again.
works fine
Thanks everybody for your response. I was on the boat today and I had it hooked up down bellow and it was working perfect. I have a Garmin for the car and it won't work indoors. I still need to mount the one on the boat some place permanently. I liked rads idea but I'm not sure how to run the wires. Anybody know if the wires can be run in the steering housing?
Thanks everybody for your response. I was on the boat today and I had it hooked up down bellow and it was working perfect. I have a Garmin for the car and it won't work indoors. I still need to mount the one on the boat some place permanently. I liked rads idea but I'm not sure how to run the wires. Anybody know if the wires can be run in the steering housing?
Have a Garmin 192C, works fine.
I have a garmin 192C, internal antenna, mounted at the wheel and under a large bimini, absolutely no problems.
I have a garmin 192C, internal antenna, mounted at the wheel and under a large bimini, absolutely no problems.
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