Just had an email from a friend having prob setting up his GPS/iPaq combination and my initial thought was the 8/8 cloud cover today so I took my GPS/iPaq outside and got 'GPS not Found' message the same as my friend.
Then took handheld eTrex outside and after 5 minutes it still can't fix on any sats? I'm not thinking this is nothing out of the ordinary, but it's something I hadn't thought about too much in the past and being a newcomer to GPS/iPaq suppose it's something I'll have to get used to.
On Thu, 30 Jun 2005 16:36:25 +1000, HC <IHateS...@home.com> wrote: >Just had an email from a friend having prob setting up his GPS/iPaq >combination and my initial thought was the 8/8 cloud cover today so I >took my GPS/iPaq outside and got 'GPS not Found' message the same as my >friend.
>Then took handheld eTrex outside and after 5 minutes it still can't fix >on any sats? I'm not thinking this is nothing out of the ordinary, but >it's something I hadn't thought about too much in the past and being a >newcomer to GPS/iPaq suppose it's something I'll have to get used to.
>Any thoughts? or suggestions? >Bronwyn ;-)
No, it's not clouds. Even Wired magazine's just reported that a user may have problems on an overcast day, but it's all BS.
I suppose clouds could have some theoretical (but probably unmeasureable) impact on reception. Your eTrex's inability to find satellites is a common "cold start" reaction for all GPSs. If the GPS is moved hundreds of miles (while powered down), or a lot of time passes between uses, it will have to re-initialize its position. This invloves a lot of data gathering, and a strat-up time of up to 15 minutes is possible, although just a few minutes is more likely. For "warm" re-starts where the GPS has been powered off for only a short time and has not been moved significantly from its last position, this time will be much shorter.
> Just had an email from a friend having prob setting up his GPS/iPaq > combination and my initial thought was the 8/8 cloud cover today so I took > my GPS/iPaq outside and got 'GPS not Found' message the same as my friend.
> Then took handheld eTrex outside and after 5 minutes it still can't fix on > any sats? I'm not thinking this is nothing out of the ordinary, but it's > something I hadn't thought about too much in the past and being a newcomer > to GPS/iPaq suppose it's something I'll have to get used to.
HC wrote: > Just had an email from a friend having prob setting up his GPS/iPaq > combination and my initial thought was the 8/8 cloud cover today so I > took my GPS/iPaq outside and got 'GPS not Found' message the same as my > friend.
> Then took handheld eTrex outside and after 5 minutes it still can't fix > on any sats? I'm not thinking this is nothing out of the ordinary, but > it's something I hadn't thought about too much in the past and being a > newcomer to GPS/iPaq suppose it's something I'll have to get used to.
> Any thoughts? or suggestions? > Bronwyn ;-)
Sounds like RFI.
The L1 and L2 GPS signals are essentially not attenuated by fog, rain, blizzard, ice crystals or any weather condition. The GPS is designed to be an all weather navigational tool.
L1 and L2 Navigation satellite Signal Power Budget
Parameter L1 P-Code L1 C/A-Code L2 P-Code ----------------------------------------------------------------------- User minimum received power -163.0 dBw -160.0 dBw -166.0 dBw Users linear antenna gain 3.0 dB 3.0 dB 3.0 dB Free-space propagation loss 184.4 dB 184.4 dB 182.3 dB > Total atmospheric loss (weather) 2.0 dB 2.0 dB 2.0 dB Polarization mismatch loss 3.4 dB 3.4 dB 4.4 dB Required satellite EIRP +23.8 dBw +26.8 dBw +19.7 dBw Satellite Antenna gain at 14.3° 13.5 dB 13.4 dB 11.5 dB worst case Block II off-axis angle Required minimum satellite antenna +10.3 dBw +13.4 dBw +8.2 dBw input power 10.72W 21.88W 6.61W
HC wrote: > Just had an email from a friend having prob setting up his GPS/iPaq > combination and my initial thought was the 8/8 cloud cover today so I > took my GPS/iPaq outside and got 'GPS not Found' message the same as my > friend.
When you get a "GPS not found", I would think that's telling you that the iPaq isn't finding the GPS and has nothing to do with the satellites.
My eTrex hasn't been turned on for some time and I probably didn't wait outside in the rain long enough for it get a fix.
Rain has stopped now so I might try them both again later....had something more pressing today. I guessed GPS would still work in planes in bad weather but wondered if those type received a stronger signal? Only guessing here! Thanks again to all who replied.
>> Just had an email from a friend having prob setting up his GPS/iPaq >> combination and my initial thought was the 8/8 cloud cover today so I >> took my GPS/iPaq outside and got 'GPS not Found' message the same as >> my friend.
> When you get a "GPS not found", I would think that's telling you that > the iPaq isn't finding the GPS and has nothing to do with the satellites.
> My eTrex hasn't been turned on for some time and I probably didn't wait > outside in the rain long enough for it get a fix.
> Rain has stopped now so I might try them both again later....had > something more pressing today. I guessed GPS would still work in planes > in bad weather but wondered if those type received a stronger signal? > Only guessing here! Thanks again to all who replied.
Is it in a case? I've heard that wet cloth cases _can_ interfere with signal quality. I've never tested this myself, and am somewhat doutbful ... but received dire warnings that the wet Magellan SporTrak case could absorb enough microwaves to be a problem.
> Is it in a case? I've heard that wet cloth cases _can_ interfere with > signal quality. I've never tested this myself, and am somewhat > doutbful
No need to be - it's true.
The GPS signals will not be affected by clouds, rain, fog, snow, etc., because of the combination of their passing through water vapour, and the signal wavelength meaning they "pass through" rain etc.
On the other hand, water will block/attenuate GPS signals. For example, you can't receive GPS signals underwater, although having a GPS receiver antenna very close to the water surface may allow some reception.
Most cloth that would be covering a GPS receiver's antenna will pass GPS signals(e.g. backpack, jacket, etc.), but cloth with a metallic component will block/attenuate the signals.
Cloth that covers a GPS receiver's antenna and gets wet (e.g. from rain) can also block/attenuate the GPS signals. In fact, you don't even need the cloth - water on the case that covers the GPS receiver antenna can block/attenuate the GPS signals. That water could be drops, and/or a film of water. I've seen that happen myself, when using my etrex Venture in the rain - the signals were weak/blocked, but a quick drying-off of the GPS case over the antenna brought the reception back, which then degraded again as water accumulated on the case. Similarly, GPS signal reception is degraded in wet forest canopy conditions compared to when the forest canopy is dry.
> > Is it in a case? I've heard that wet cloth cases _can_ interfere with > > signal quality. I've never tested this myself, and am somewhat > > doutbful
> No need to be - it's true.
> The GPS signals will not be affected by clouds, rain, fog, > snow, etc., because of the combination of their passing > through water vapour, and the signal wavelength meaning > they "pass through" rain etc.
OK, I recognize that we are basically trying to receive microwave signals, but... I don't see a really big hit from moderate foliage, which doesn't seem all that different, in terms of liquid water content/thickness.
>>>Is it in a case? I've heard that wet cloth cases _can_ interfere with >>>signal quality. I've never tested this myself, and am somewhat >>>doutbful
>>No need to be - it's true.
>>The GPS signals will not be affected by clouds, rain, fog, >>snow, etc., because of the combination of their passing >>through water vapour, and the signal wavelength meaning >>they "pass through" rain etc.
> OK, I recognize that we are basically trying to receive microwave signals, > but... > I don't see a really big hit from moderate foliage, which doesn't seem all > that different, in terms of liquid water content/thickness.
Each leaf in the foliage is fairly small and quite far removed from the receiver. That allows diffraction of the microwaves around the edges of the leaf to still result in significant signal getting through. A wet cloth directly over the antenna can be more effective at blocking the signals even if the total water content is similar.
I didn't have my iPaq/GPS in a case but my eTrex is in a leather case, maybe next time I'll try undoing the clip at the top where the antenna is located and see what happens.
I knew foliage blocked signals but thought it was because the sky was physically blocked by the leaves, so I've learned quite a bit by these replies. Also I didn't know the GPS wouldn't receive a signal underwater, but then again I've never tried to use on in that situation either. LOL
>>>> Is it in a case? I've heard that wet cloth cases _can_ interfere with >>>> signal quality. I've never tested this myself, and am somewhat >>>> doutbful
>>> No need to be - it's true.
>>> The GPS signals will not be affected by clouds, rain, fog, >>> snow, etc., because of the combination of their passing >>> through water vapour, and the signal wavelength meaning >>> they "pass through" rain etc.
>> OK, I recognize that we are basically trying to receive microwave >> signals, >> but... >> I don't see a really big hit from moderate foliage, which doesn't seem >> all >> that different, in terms of liquid water content/thickness.
> Each leaf in the foliage is fairly small and quite far removed from the > receiver. That allows diffraction of the microwaves around the edges of > the leaf to still result in significant signal getting through. A wet > cloth directly over the antenna can be more effective at blocking the > signals even if the total water content is similar.
(1) A very wet (left out in the rain overnight) neoprene wrap-around case for a Magellan SporTrak Pro caused an almost complete block of the signal.. Yes - a wet case can block the signal. (2) As indicated in the post below, a single leaf is usually small and somewhat remote, so the blocking of signals is not as dramatic. Generally however, leaves come in groups of more than one! When I map trails here in upstate NY, I prefer to do it in winter when the leaves are off the hardwoods. The lack of moist leaf cover will improve fix accuracy somewhat. Of course, if you have snow covered pines, that doesn't help.
>>>>Is it in a case? I've heard that wet cloth cases _can_ interfere with >>>>signal quality. I've never tested this myself, and am somewhat >>>>doutbful
>>>No need to be - it's true.
>>>The GPS signals will not be affected by clouds, rain, fog, >>>snow, etc., because of the combination of their passing >>>through water vapour, and the signal wavelength meaning >>>they "pass through" rain etc.
>> OK, I recognize that we are basically trying to receive microwave >> signals, >> but... >> I don't see a really big hit from moderate foliage, which doesn't seem >> all >> that different, in terms of liquid water content/thickness.
> Each leaf in the foliage is fairly small and quite far removed from the > receiver. That allows diffraction of the microwaves around the edges of > the leaf to still result in significant signal getting through. A wet > cloth directly over the antenna can be more effective at blocking the > signals even if the total water content is similar.
The message "GPS Not Found" indicates that the GPS somehow fails to make connections to your iPaq -- a hardware problem and it should have nothing to do with whether your GPS is having problems acquiring. In this case, you should have the the satellite page showing only a few satellites... this is one of the reason I dislike PDA-based GPS. I have a Palm and a Magellan GPS plugin that occasionally gives me that darn "GPS Not Found" message. A few wiggle and power on/off would take care of it but it's annoying none the less.
I have a Garmin 2610 (without external antenna) and one time had driven 6 continuous hours in pouring rain and the sky so dark it could pass for night without once losing signals so I don't think clouds, rain and water on the windshield have that much effect on GPS's ability to acquire satellites.
> The message "GPS Not Found" indicates that the GPS somehow fails to > make connections to your iPaq -- a hardware problem and it should have > nothing to do with whether your GPS is having problems acquiring.
That may not be true -- with my old Magellan 315 (and I think the Meridian Gold, but have not verified this), until it aquired that sats, there was NO NMEA output. I too spent time trying to figure out why it would not see the GPS until I used hyperterminal connected to the GPS and noticed until it had a fix, there was NO nmea output. With no output, your application will not see it. One of those "duh" moments as it were.
> In this case, you should have the the satellite page showing only a few > satellites... this is one of the reason I dislike PDA-based GPS. I > have a Palm and a Magellan GPS plugin that occasionally gives me that > darn "GPS Not Found" message. A few wiggle and power on/off would take > care of it but it's annoying none the less.
> I have a Garmin 2610 (without external antenna) and one time had driven > 6 continuous hours in pouring rain and the sky so dark it could pass > for night without once losing signals so I don't think clouds, rain and > water on the windshield have that much effect on GPS's ability to > acquire satellites.
DiverHank wrote: > The message "GPS Not Found" indicates that the GPS somehow fails to > make connections to your iPaq -- a hardware problem and it should have > nothing to do with whether your GPS is having problems acquiring. In > this case, you should have the the satellite page showing only a few > satellites... this is one of the reason I dislike PDA-based GPS. I > have a Palm and a Magellan GPS plugin that occasionally gives me that > darn "GPS Not Found" message. A few wiggle and power on/off would take > care of it but it's annoying none the less.
That's what I told them about ten posts ago, but I guess no one believed it.
>> The message "GPS Not Found" indicates that the GPS somehow fails to >> make connections to your iPaq -- a hardware problem and it should have >> nothing to do with whether your GPS is having problems acquiring. In >> this case, you should have the the satellite page showing only a few >> satellites... this is one of the reason I dislike PDA-based GPS. I >> have a Palm and a Magellan GPS plugin that occasionally gives me that >> darn "GPS Not Found" message. A few wiggle and power on/off would take >> care of it but it's annoying none the less.
> That's what I told them about ten posts ago, but I guess no one believed > it.
The L1 and L2 GPS signals are essentially not attenuated by fog, rain, blizzard, ice crystals or any weather condition. The GPS is designed to be an all weather navigational tool.
L1 and L2 Navigation satellite Signal Power Budget
Parameter L1 P-Code L1 C/A-Code L2 P-Code ----------------------------------------------------------------------- User minimum received power -163.0 dBw -160.0 dBw -166.0 dBw Users linear antenna gain 3.0 dB 3.0 dB 3.0 dB Free-space propagation loss 184.4 dB 184.4 dB 182.3 dB > Total atmospheric loss (weather) 2.0 dB 2.0 dB 2.0 dB Polarization mismatch loss 3.4 dB 3.4 dB 4.4 dB Required satellite EIRP +23.8 dBw +26.8 dBw +19.7 dBw Satellite Antenna gain at 14.3° 13.5 dB 13.4 dB 11.5 dB worst case Block II off-axis angle Required minimum satellite antenna +10.3 dBw +13.4 dBw +8.2 dBw input power 10.72W 21.88W 6.61W
Sam Wormley wrote... > The L1 and L2 GPS signals are essentially not attenuated by fog, rain, > blizzard, ice crystals or any weather condition. The GPS is designed to > be an all weather navigational tool. > ... > L1 and L2 Navigation satellite Signal Power Budget
> Parameter L1 P-Code L1 C/A-Code L2 P-Code > Total atmospheric loss (weather) 2.0 dB 2.0 dB 2.0 dB
I think that the strict answer to the question is yes it does, but not significantly. According to Sam's figures (snipped above) the worst-weather signal loss due to the atmosphere is only 2dB which equates to a loss of only 37%, which is not at all significant. In sound terms a difference of 2dB is just the difference between a car-horn and a loud personal stereo.
I was in Korea several weeks ago using my GPS to find my way back to the hotel. It was working fine until one morning there was low clouds and drizzle. I was getting poor reception to the tune of one or two barely visible satellites. As the storm moved on, I started to get better reception. HOWEVER! The other day it was raining here in Utah (surprise) and I had just a slight signal loss.
