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GPS antenna location
I have been getting conflicting advice about relative position in
regard to my radar dome. Both will be mounted on my mast about 12 to 24 inches apart. I have a choice of having the GPS right below the bottom of the dome or I could put an extension and have it extend a few inches above the dome. Any advice? Thanks Bob |
GPS antenna location
On Mon, 21 Jan 2008 09:51:04 -0800 (PST), Rob
wrote in : I have been getting conflicting advice about relative position in regard to my radar dome. Both will be mounted on my mast about 12 to 24 inches apart. I have a choice of having the GPS right below the bottom of the dome or I could put an extension and have it extend a few inches above the dome. Any advice? Why put your GPS antenna way up there? GPS works well as long as it has a clear view of the sky, and it's best to keep the cable run as short as possible. I've not had any problems with antennas mounted on the stern pulpit. -- Best regards, John Navas http:/navasgroup.com |
GPS antenna location
Rob wrote:
I have been getting conflicting advice about relative position in regard to my radar dome. Both will be mounted on my mast about 12 to 24 inches apart. I have a choice of having the GPS right below the bottom of the dome or I could put an extension and have it extend a few inches above the dome. Any advice? Thanks BoB Your mast will mask out quite a few of the satellites and make reception difficult. Set it on the pulpit rail away from any object that may prevent a view of the whole sky. The height is quite irrelevant for GPS reception. Dennis. |
GPS antenna location
In article
, Rob wrote: I have been getting conflicting advice about relative position in regard to my radar dome. Both will be mounted on my mast about 12 to 24 inches apart. I have a choice of having the GPS right below the bottom of the dome or I could put an extension and have it extend a few inches above the dome. Any advice? Thanks Bob Well, since GPS and XBand Radar use different, and Widely separated, frequencies, the only real, or apparent, problems should be the effect of the RF Peak Pulse Output, of the Radar, mixing, or overloading in the Frontend of the GPS's Antenna Mounted Preamp. This could be mitigated by mounting the GPS Antenna Unit, outside the Radars, Vertical Antenna Pattern, which is typically, Plus or Minus 12 degrees from the horizon. Now, if you put the GPS Antenna, BELOW the Radar, the Radar itself will block some reception from above, where is shades the GPS Antenna. If you mount the GPS Antenna DIRECTLY above the Radar, No Problems. If you mount it off to the side of the Radar, then you should position it, WELL OUTSIDE the Radar Antennas Vertical Beamwidth, and more distance is better, due to our old friend, Inverse Square Law. -- Bruce in alaska add path after fast to reply |
GPS antenna location
Rob wrote:
I have been getting conflicting advice about relative position in regard to my radar dome. Both will be mounted on my mast about 12 to 24 inches apart. I have a choice of having the GPS right below the bottom of the dome or I could put an extension and have it extend a few inches above the dome. Any advice? Thanks Bob I put mine on top of the stern arch and that's a mistake. Once in a while I get some reading of 50 knots or more. I think they are caused by the rocking or rolling of the boat. I would put the antenna as low as possible near the center of motion that has a clear view of the sky. You know there is a place on the boat that actually doesn't move. Put it there. :-) Jeannette |
GPS antenna location
Rob, in article a999739f-3fe0-4e5a-b019-94c67b451186
@v67g2000hse.googlegroups.com, says... I have been getting conflicting advice about relative position in regard to my radar dome. Both will be mounted on my mast about 12 to 24 inches apart. I have a choice of having the GPS right below the bottom of the dome or I could put an extension and have it extend a few inches above the dome. Any advice? As others have said, mount it low down with a clear view of the sky - and well away from the radar transmitter. A friend's boat had one that was mounted above a radome that wouldn't work when the radar was running. Apparently, the cable going up to the GPS antenna routed in front of the radar antenna wasn't a good idea... :-) Mounting it high up on a sailing boat also makes it subject to position reporting error due to heel, not to mention confusing it when rolling. -- JohnW. Replace the obvious with co.uk in 2 places to mail me. |
GPS antenna location
On Mon, 21 Jan 2008 09:51:04 -0800 (PST), Rob
wrote: I have been getting conflicting advice about relative position in regard to my radar dome. Both will be mounted on my mast about 12 to 24 inches apart. I have a choice of having the GPS right below the bottom of the dome or I could put an extension and have it extend a few inches above the dome. Any advice? Thanks Bob Either is fine, as long as the GPS antenna is clearly outside of the radar beam. (Although on a previous boat, an ancient GPS antenna/receiver was mounted about a foot from a 4 KW radar scanner, right in the beam, with no apparent problems.) -- Peter Bennett, VE7CEI peterbb4 (at) interchange.ubc.ca GPS and NMEA info: http://vancouver-webpages.com/peter Vancouver Power Squadron: http://vancouver.powersquadron.ca |
GPS antenna location
On Mon, 21 Jan 2008 09:51:04 -0800 (PST), Rob
wrote: I have been getting conflicting advice about relative position in regard to my radar dome. Both will be mounted on my mast about 12 to 24 inches apart. I have a choice of having the GPS right below the bottom of the dome or I could put an extension and have it extend a few inches above the dome. Any advice? Thanks Bob Disregard my previous post (although it is correct about keeping the GPS antenna out of the radar beam). As others have said, the GPS antenna should be mounted fairly low on the boat, and in a location where it has a clear view of the sky in all directions. Mounting the GPS antenna on the mast will cause it to see spurious movements as the boat rocks. In addition, if the GPS antenna is immediately below the radar scanner, the scanner will block the GPS satellite signals from a fair portion of the sky. -- Peter Bennett, VE7CEI peterbb4 (at) interchange.ubc.ca GPS and NMEA info: http://vancouver-webpages.com/peter Vancouver Power Squadron: http://vancouver.powersquadron.ca |
GPS antenna location
Is this a sailboat? I assumed powerboat with an electronics mast. If
it is sail, get it low and clear (as all the other posters suggested). If power and you only have the mast space then separate as far apart and I prefer BELOW the beam of the radar. I have 3 on my hardtop, all mounted within 24" of an open array 4KW but all just below the beam. No SNR issues at all. Rob wrote: I have been getting conflicting advice about relative position in regard to my radar dome. Both will be mounted on my mast about 12 to 24 inches apart. I have a choice of having the GPS right below the bottom of the dome or I could put an extension and have it extend a few inches above the dome. Any advice? Thanks Bob |
GPS antenna location
it's best to keep the cable run as short as possible.
Which is usless advice if it's a network-connected GPS antenna. NMEA2000, SeaTalk, etc, are fine with longer cable runs. You don't mention if this is a power or sail vessel. Generally you want your GPS unit mounted where it's going to have an unobstructed view of the sky. Putting it next to a radome might be a problem in that the signal would be getting blocked. Not enough to entirely lose all fix but enough to degrade the overall accuracy of it. -Bill Kearney |
GPS antenna location
On Tue, 22 Jan 2008 00:24:09 -0500, "Bill Kearney"
wrote in : it's best to keep the cable run as short as possible. Which is usless advice if it's a network-connected GPS antenna. ... And sound advice if it's a passive antenna, as is often used on smaller boats. -- Best regards, John Navas http:/navasgroup.com |
GPS antenna location
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GPS antenna location
larry wrote:
Rob wrote in news:a999739f-3fe0-4e5a-b019- : I have been getting conflicting advice about relative position in regard to my radar dome. Both will be mounted on my mast about 12 to 24 inches apart. I have a choice of having the GPS right below the bottom of the dome or I could put an extension and have it extend a few inches above the dome. Any advice? Thanks Bob Wrong attitude. The GPS antenna has no need for ALTITUDE. Aboard Lionheart, I got tired of them bumping into both the Raystar little dome and the Garmin active antenna, so I mounted them INSIDE the overhead cabinet in the galley Belowdecks is the way to go in a fiberglass boat. My friend held the antenna alternately in the clear abovedecks, and belowdecks hard up against the coachroof in various spots. I watched the signal strength indicator on the chartplotter as she moved the antenna between the abovedecks and belowdecks positions. In many spots belowdecks there was no difference in signal strength from the satellites with the antenna abovedecks or belowdecks. My GPS antenna is now mounted in a good spot belowdecks, out of the weather, away from running rigging and flying feet. |
GPS antenna location
Moonshadow wrote:
larry wrote: Rob wrote in news:a999739f-3fe0-4e5a-b019- : I have been getting conflicting advice about relative position in regard to my radar dome. Both will be mounted on my mast about 12 to 24 inches apart. I have a choice of having the GPS right below the bottom of the dome or I could put an extension and have it extend a few inches above the dome. Any advice? Belowdecks is the way to go in a fiberglass boat. My friend held the antenna alternately in the clear abovedecks, and belowdecks hard up against the coachroof in various spots. I watched the signal strength indicator on the chartplotter as she moved the antenna between the abovedecks and belowdecks positions. In many spots belowdecks there was no difference in signal strength from the satellites with the antenna abovedecks or belowdecks. My GPS antenna is now mounted in a good spot belowdecks, out of the weather, away from running rigging and flying feet. Better yet, get an internal antenna version of the unit, it has optimal connectivity with no cabling. My Garmin GPSMAP 172C is mounted inside a pilothouse and always hits on any satellite shown above the horizon, without problem. |
GPS antenna location
Always best to get the GPS antenna some distance from the radar and out of
the direct beam of the radar. I agree that low down is generally ok. Mine is inside the fibreglass flybridge with no apparent ill effects! Alec "Rob" wrote in message ... I have been getting conflicting advice about relative position in regard to my radar dome. Both will be mounted on my mast about 12 to 24 inches apart. I have a choice of having the GPS right below the bottom of the dome or I could put an extension and have it extend a few inches above the dome. Any advice? Thanks Bob |
GPS antenna location
On Tue, 22 Jan 2008 19:40:30 +1100, Moonshadow
wrote in : larry wrote: Wrong attitude. The GPS antenna has no need for ALTITUDE. Aboard Lionheart, I got tired of them bumping into both the Raystar little dome and the Garmin active antenna, so I mounted them INSIDE the overhead cabinet in the galley Belowdecks is the way to go in a fiberglass boat. My friend held the antenna alternately in the clear abovedecks, and belowdecks hard up against the coachroof in various spots. I watched the signal strength indicator on the chartplotter as she moved the antenna between the abovedecks and belowdecks positions. In many spots belowdecks there was no difference in signal strength from the satellites with the antenna abovedecks or belowdecks. My GPS antenna is now mounted in a good spot belowdecks, out of the weather, away from running rigging and flying feet. My own tests have been quite different -- I've seen considerable difference between belowdecks and abovedecks, and agree with manufacturers recommendations to mount the antenna on something like the stern pulpit. It makes no sense to take _any_ risk with something this critical to safety. -- Best regards, John Navas http:/navasgroup.com |
GPS antenna location
Why do people persist in putting their GPS antenna on the stern rail. Is it
not one of your most important instruments? Do you want it to be yanked off by some clumsy git climbing aboard from a dinghy or clipped off by a shoreline? I have always mounted mine on the stern but directly on the deck where it out of everyone's way. It also gets a perfect view of the sky without the pendulum movement of a mast mounting. This is on my third boat and I have never had one damaged. How many people keep a spare GPS aerial for these eventualities? "Alec" wrote in message ... Always best to get the GPS antenna some distance from the radar and out of the direct beam of the radar. I agree that low down is generally ok. Mine is inside the fibreglass flybridge with no apparent ill effects! Alec "Rob" wrote in message ... I have been getting conflicting advice about relative position in regard to my radar dome. Both will be mounted on my mast about 12 to 24 inches apart. I have a choice of having the GPS right below the bottom of the dome or I could put an extension and have it extend a few inches above the dome. Any advice? Thanks Bob |
GPS antenna location
Nicholas Walsh wrote:
Why do people persist in putting their GPS antenna on the stern rail. Is it not one of your most important instruments? Do you want it to be yanked off by some clumsy git climbing aboard from a dinghy or clipped off by a shoreline? I have always mounted mine on the stern but directly on the deck where it out of everyone's way. It also gets a perfect view of the sky without the pendulum movement of a mast mounting. This is on my third boat and I have never had one damaged. How many people keep a spare GPS aerial for these eventualities? Mine's coachroof mounted 'limpet' style on our Contessa 26 with excess cable shortened and a new BNC plug put on. It's predecessor used to be mounted on a stancheon supporting the mainsheet horse and that was a nightmare. If it didn't get knocked by the mainsheet, someone would lean back over it and block the signal, or a warp would abrade its cable etc. I give the new one a gentle polish a couple of times a season to keep the water beading up and running off and I get a *far* better signal. I've replaced the cable into the old one and tested it for a spare just in case though. -- Ian Malcolm. London, ENGLAND. (NEWSGROUP REPLY PREFERRED) ianm[at]the[dash]malcolms[dot]freeserve[dot]co[dot]uk [at]=@, [dash]=- & [dot]=. *Warning* HTML & 32K emails -- NUL: 'Stingo' Albacore #1554 - 15' Early 60's, Uffa Fox designed, All varnished hot moulded wooden racing dinghy. |
GPS antenna location
On Mon, 21 Jan 2008 19:52:29 -0000, JohnW
wrote: Mounting it high up on a sailing boat also makes it subject to position reporting error due to heel, not to mention confusing it when rolling. I was under the impression that GPS results are referenced to the location of the antenna. So what does heel have to do with it? Casady |
GPS antenna location
Richard Casady, in article 47b6d18e.1524399671
@news.east.earthlink.net, says... I was under the impression that GPS results are referenced to the location of the antenna. So what does heel have to do with it? When you are heeled over, the antenna, if up the mast, will be over to the side somewhere, some distance from the boat centerline where it will be giving an incorrect position report for the boat. Since heel isn't constant, the error introduced by heel would be variable. Not that you should be using the position information reported by GPS to that level of accuracy anyway :-) However, there have been several GPS assisted collisions with fixed landscape features, so perhaps that isn't true anymore? If you are pitching and rolling, the antenna will be moving relative to the boat so the GPS will include that motion in with the boat's forward velocity in its speed calculation. --- One problem with mounting the antenna at deck level, under the pushpit, is that from a dinghy, it looks too much like a handle to help getting on deck. If on the pushpit, it can get knocked. I have mine under the GPS structure which has no reported signal strength implications. It also isn't a visible "I've got a GPS available for stealing" signal... -- JohnW. Replace the obvious with co.uk in 2 places to mail me. |
GPS antenna location
On Sun, 27 Jan 2008 12:08:31 -0000, JohnW
wrote: When you are heeled over, the antenna, if up the mast, will be over to the side somewhere, some distance from the boat centerline where it will be giving an incorrect position report for the boat. Since heel isn't constant, the error introduced by heel would be variable. Well yeah. I dismissed that kind of thing as too trivial to worry about. Not that you should be using the position information reported by GPS to that level of accuracy anyway I think that when feet matter, eyes should be on something else, the world, the sonar, the radar, something. Maybe even an occasional glance at the engine gauges. Basically GPS gives position. Mariners used to find that out once a day, with the sextant, to an accuracy of no better than half a mile. How soon we forget. Soon third world despots will be able to disappear the system. I am hanging on to my sextant, just in case. Iran with ASAT? Casady |
GPS antenna location
JohnW wrote in
: If you are pitching and rolling, the antenna will be moving relative to the boat so the GPS will include that motion in with the boat's forward velocity in its speed calculation. - Y'all give a cheap boat GPS WAY too much credit for position fixes! It's only good to about 3 feet, on a sunny day, with no reflecting airplanes making multipath signals, far out away from any land. Boat GPSes are NOT GPS surveying instruments like the Geodetic Survey little Japanese guy who comes to my house to check the fault line I live on for movement in mm every month. God help any of you that think that cheap piece of crap in the plastic box is gonna put you within 5 ft of the bouy in the fog. It's just NOT accurate to inches.....EVER. Here, test it at the dock. Turn it on and clear its bread trails. Leave it on sitting dead still at the dock in perfectly flat water until tomorrow. See if it stays within 5 ft for a day sitting still. It won't, but you need to know and NOT trust it so much. If you live in a metro area with an airport, the aluminum clouds flying by will make it really go crazy over the course of a day, suddenly jumping way down the dock, then jumping back as the aluminum clouds move around. GPS works on the phase relationships between precisely pulsed microwave signals from 3 or more overhead birds. If you change the PATH from the birds to the GPS, huge errors are introduced into the GPS phase relationships. If you have a handheld GPS, carry it into the burger joint on a busy road and let it bread trail on close range. The signal can't get through the roof so what the GPS receives are signals bouncing off objects outside, like passing vehicles and stationary (we hope) buildings through the big windows. Let it run an hour and its fix will cover the whole shopping center....many hundred feet! This same effect happens in a HARBOR or the ICW! Signals bouncing off nearby conductive objects, especially overhead bridges, just eats it alive. Anywhere near shore a GPS fix gets wider and wider in accuracy because of multipath, the same signal bouncing that tears up a UHF TV signal on an old analog TV with "ghosts", signals arriving later than the main signal which ALWAYS make ghosts to the RIGHT of the main signal, because they arrive later...we scan from left to right, top to bottom like reading a page in a book....except every other line, called interlacing to make it flicker less. All this terror over the motion of the mast is just crazy! The mast, itself, and all your rigging to any GPS antenna on the deck is causing multipath signals from the overhead birds....and screwing up the timing. Ever wonder why it only updates every second? It's trying to average out the MULTIPATH MOVEMENT ITS MEASURING! |
GPS antenna location
In article ,
larry wrote: Y'all give a cheap boat GPS WAY too much credit for position fixes! It's only good to about 3 feet, on a sunny day, with no reflecting airplanes making multipath signals, far out away from any land. I guess that is still very optimistic - 15-20 m, ie 50-60 ft are more like it. If you use SDGPS with corrections by satellites, it might come down to 3 m, or 10 ft. No way navigating a channel with 3 m leeway on each side by GPS (even SDGPS). Tested! In perfect conditions ... HTH Marc -- remove bye and from mercial to get valid e-mail http://www.heusser.com |
GPS antenna location
On Sun, 27 Jan 2008 17:05:39 +0100, Marc Heusser
d wrote in : In article , larry wrote: Y'all give a cheap boat GPS WAY too much credit for position fixes! It's only good to about 3 feet, on a sunny day, with no reflecting airplanes making multipath signals, far out away from any land. I guess that is still very optimistic - 15-20 m, ie 50-60 ft are more like it. If you use SDGPS with corrections by satellites, it might come down to 3 m, or 10 ft. No way navigating a channel with 3 m leeway on each side by GPS (even SDGPS). Tested! In perfect conditions ... I've done considerable testing of my modest Magellan Sportrak Color, and with a clear view of the sky it's repeatable to within 10-20 feet, even in major metro areas, quite capable of navigating real world narrow channels, albeit not as narrow as your hypothetical case of 3 m on each side. -- Best regards, John Navas http:/navasgroup.com |
GPS antenna location
On Sun, 27 Jan 2008 15:15:32 +0000, larry wrote in
: JohnW wrote in : If you are pitching and rolling, the antenna will be moving relative to the boat so the GPS will include that motion in with the boat's forward velocity in its speed calculation. Plus interference with direction over ground calculations due to rocking from side to side. If you have a handheld GPS, carry it into the burger joint on a busy road and let it bread trail on close range. The signal can't get through the roof so what the GPS receives are signals bouncing off objects outside, like passing vehicles and stationary (we hope) buildings through the big windows. Let it run an hour and its fix will cover the whole shopping center....many hundred feet! This same effect happens in a HARBOR or the ICW! Signals bouncing off nearby conductive objects, especially overhead bridges, just eats it alive. Anywhere near shore a GPS fix gets wider and wider in accuracy because of multipath, the same signal bouncing that tears up a UHF TV signal on an old analog TV with "ghosts", signals arriving later than the main signal which ALWAYS make ghosts to the RIGHT of the main signal, because they arrive later...we scan from left to right, top to bottom like reading a page in a book....except every other line, called interlacing to make it flicker less. I record NMEA output from my Magellan Sportrak Color GPS on my laptop, and I'm not seeing that kind of error -- my tracks are quite accurate when checked on the charts on my laptop. Ever wonder why it only updates every second? It's trying to average out the MULTIPATH MOVEMENT ITS MEASURING! It's actually feeding valuable real-time data to my laptop, which is automatically computing and displaying target speed polars in real time. -- Best regards, John Navas http:/navasgroup.com |
GPS antenna location
On Sat, 26 Jan 2008 18:44:41 -0000, "Nicholas Walsh"
wrote in : Why do people persist in putting their GPS antenna on the stern rail. Is it not one of your most important instruments? Do you want it to be yanked off by some clumsy git climbing aboard from a dinghy or clipped off by a shoreline? I have always mounted mine on the stern but directly on the deck where it out of everyone's way. It also gets a perfect view of the sky without the pendulum movement of a mast mounting. This is on my third boat and I have never had one damaged. How many people keep a spare GPS aerial for these eventualities? In my experience the stern pulpit rail is safer -- I've seen too many people kick an antenna mounted at deck level. I always have at least two hand-held units to back up the boat GPS. -- Best regards, John Navas http:/navasgroup.com |
GPS antenna location
John Navas wrote:
On Sun, 27 Jan 2008 15:15:32 +0000, larry wrote in : JohnW wrote in : If you are pitching and rolling, the antenna will be moving relative to the boat so the GPS will include that motion in with the boat's forward velocity in its speed calculation. Plus interference with direction over ground calculations due to rocking from side to side. If you have a handheld GPS, carry it into the burger joint on a busy road and let it bread trail on close range. The signal can't get through the roof so what the GPS receives are signals bouncing off objects outside, like passing vehicles and stationary (we hope) buildings through the big windows. Let it run an hour and its fix will cover the whole shopping center....many hundred feet! This same effect happens in a HARBOR or the ICW! Signals bouncing off nearby conductive objects, especially overhead bridges, just eats it alive. Anywhere near shore a GPS fix gets wider and wider in accuracy because of multipath, the same signal bouncing that tears up a UHF TV signal on an old analog TV with "ghosts", signals arriving later than the main signal which ALWAYS make ghosts to the RIGHT of the main signal, because they arrive later...we scan from left to right, top to bottom like reading a page in a book....except every other line, called interlacing to make it flicker less. I record NMEA output from my Magellan Sportrak Color GPS on my laptop, and I'm not seeing that kind of error -- my tracks are quite accurate when checked on the charts on my laptop. Ever wonder why it only updates every second? It's trying to average out the MULTIPATH MOVEMENT ITS MEASURING! It's actually feeding valuable real-time data to my laptop, which is automatically computing and displaying target speed polars in real time. I have had trucks travel all over Europe with gps tracking to a laptop, and I could consistently see, on which side of the highway those trucks traveled. No problems with cars/trucks being around, passing trafficlights, etc. Only tunnels broke the track :) And also very bad weather(high thunder clouds/extremely heavy rain). Also we used them in harbours for the british navy, in a blind course guidance experiment. Worked like a charm. Only place were we had trouble was for the same experiment inside a helicopter. Those rotorblades dont treat GPS kindly. |
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