+RobertM Posted October 5, 2002 Share Posted October 5, 2002 Hi, I'm quite certain that mist and rain doesn't effect the reception of satellite TV too much, but does it effect GPSr reception? The reason I ask is that yesterday I went find a cache I couldn't find on the first attempt a fe days earlier but this time I could get no signal on the mountain (Mt Seymour in North Vancouver). On my previous visit I got reception under the trees, but with the heavy mist under rather thick tree cover I could only get max 2 birds which didn't help. Anyone know more about this? Does mist/rain effect GPSr reception a lot? Thanks Rob Quote Link to comment
umc Posted October 5, 2002 Share Posted October 5, 2002 I have heard clouds and fog effect it so I would assume that could me the case with your mist. The reason I say that I have heard is because I have a GPS V and a GM100 and I never have noticed a problem with my GM100 but the V I have. Can't really confirm that too much since I just got the V a few days ago. ______________________________________________________________________________________ Proud New Owner Of a Garmin GPS V Received on 10-03-02 Quote Link to comment
umc Posted October 5, 2002 Share Posted October 5, 2002 Also check out this link ______________________________________________________________________________________ Proud New Owner Of a Garmin GPS V Received on 10-03-02 Quote Link to comment
+EraSeek Posted October 5, 2002 Share Posted October 5, 2002 No. Rain, fog, mist, snow is not a problem for your signal. However, it is my understanding that a wet forest cover can either inhibit a signal or can cause a greater amount of signal bounce than a dry canopy. But in the air, water is no problem. Quote Link to comment
+Whidbey Walk Posted October 5, 2002 Share Posted October 5, 2002 Them darn wet leaves!!!! Check out this information. http://www.cmtinc.com/gpsbook/chap10.html For more than you ever thought you would want to know about GPS check out this paper. The third paragraph on page 4 mentions signal bounce and wet foliage. http://www.gmat.unsw.edu.au/snap/gps/gps_notes1.pdf http://home.earthlink.net/~whidbeywalk/ Quote Link to comment
+Whidbey Walk Posted October 5, 2002 Share Posted October 5, 2002 Them darn wet leaves!!!! Check out this information. http://www.cmtinc.com/gpsbook/chap10.html For more than you ever thought you would want to know about GPS check out this paper. The third paragraph on page 4 mentions signal bounce and wet foliage. http://www.gmat.unsw.edu.au/snap/gps/gps_notes1.pdf http://home.earthlink.net/~whidbeywalk/ Quote Link to comment
+Desert_Warrior Posted October 5, 2002 Share Posted October 5, 2002 quote:Originally posted by EraSeek:No. Rain, fog, mist, snow is not a problem for your signal. However, it is my understanding that a wet forest cover can either inhibit a signal or can cause a greater amount of signal bounce than a dry canopy. But in the air, water is no problem. http://img.Groundspeak.com/user/4497_300.jpg Sorry to disagree. ANY moisture in the air WILL HAVE an effect on RF energy. The amount of effect is mostly dependant on the RF energy frequency, and the moisture density. If this were not true, weather radar would never report clouds and rain. I cannot give you the exact specs at the 1575 GPS freq, but I can tell you that at Redstone Arsenal I have personally tracked T-storms and tornados using a classified radar with a freq somewhere near the GPS area. The effect is small, but it is measurable. Under marginal conditions, it may be enough to cause you to lose the signal. 3 dB is 3dB, wether trees, rain, your hand, whatever. Mike. KD9KC. El Paso, Texas. Citizens of this land may own guns. Not to threaten their neighbors, but to ensure themselves of liberty and freedom. They are not assault weapons anymore... they are HOMELAND DEFENSE WEAPONS! Quote Link to comment
+carleenp Posted October 5, 2002 Share Posted October 5, 2002 My GPS (Magellan 315) has done fine in cloudy/misty/rainy weather. BUT, at times it would not pick up all of the available satellite positions and wouldn't average them well under those conditions. It got worse if I got under wet trees. Quote Link to comment
+leatherman Posted October 5, 2002 Share Posted October 5, 2002 I've never had any problems in the rain. Warm humid days are what make my satellite locks jump around. I was in Eugene, OR under a veil of hot humid air. I walked out on a small bridge, over a river, and my GPSr went crazy. I watched the satellites jump up and down for about 15 minutes. At one point it showed my in Vietnam. There were no obstructions for miles. My reception didn't improve 'till I drove out of the humid valley. Preparation, the first law to survival. Mokita! Quote Link to comment
+Zahrim Posted October 6, 2002 Share Posted October 6, 2002 I have never taken my new MeriGold out in the rain yet, but I have had a satellite TV system for well over 6 years, and I can tell you for a fact that if it starts to rain "real" hard I lose signal very fast, and for as long as there is a hard rain going on. On a side note, a tornado will also block the signal for a satellite TV receiver. I live just a mile from where the 3 May 1999 tornado came through Midwest City Oklahoma. quote:Originally posted by RobertM:Hi, I'm quite certain that mist and rain doesn't effect the reception of satellite TV too much, but does it effect GPSr reception? The reason I ask is that yesterday I went find a cache I couldn't find on the first attempt a fe days earlier but this time I could get no signal on the mountain (Mt Seymour in North Vancouver). On my previous visit I got reception under the trees, but with the heavy mist under rather thick tree cover I could only get max 2 birds which didn't help. Anyone know more about this? Does mist/rain effect GPSr reception a lot? Thanks Rob Zahrim.... "There's no need to be afraid of strange noises in the night. Anything that intends you harm will stalk you silently." Quote Link to comment
dave and jaime Posted October 6, 2002 Share Posted October 6, 2002 what happens is the rain droplets diffuse the signal and the reciever recieves confusing information, each satalitte sends its own signature code and when the moisture in the air causes parts of it to take a longer time to reach the reciever it gives the reciever the impression it is at a different location (it may also show you moving when you are still). in very humid air the diffusion of signal may cause enough interference that the signal isn't strong enough to reach the reciever. generally speaking todays gps were built with this in mind and can compensate for it, however when using gps in these conditions it is something to be aware of. Quote Link to comment
crr003 Posted October 6, 2002 Share Posted October 6, 2002 Below 10 GHz rain is reportedly of little problem for signal attenuation. (GPS is at 1.5 GHz). Neither Garmin nor Trimble web sites mention it as a cause of error. Here's a quote from a satellite company: "Therefore, transmissions at 6/4 GHz will experience insignificant attenuation, while transmissions at 14/12 GHz will experience greater attenuation. For 6/4 GHz signals to be affected would require rain storms approaching hurricane conditions." GPS frequency is lower so would be bothered even less. Also, think about this - GPS is being put forward as a system to navigate and land 'planes. I don't think this would be acceptable if rain could disturb it badly? Nil Satis Nisi Optimum Quote Link to comment
+RobertM Posted October 7, 2002 Author Share Posted October 7, 2002 Hi, Some interesting info and different points of views. Even in the open while driving to the mountain I had a problem picking up signals. Normally while driving I can pick quite a couple but on the misty/rainy day I picked up sometimes 1 and 4 in the open. So in my opinion the only factor here was the rain/mist. Windshield wipers weren't in use either. :-) Then under the cover a few days before I could pick up 3 to 4 signals through the openings in the tree cover. In the rain/mist I could only pick up 1 signal, sometimes 2, but not more. So under the cover I normally pick up less signals and under rain/mist with less signals "coming through" I'd obviously pick up less signals under the cover, which makes sense. The wet leaves thing therefore is questionable, right? It's what's above the trees, i.e. rain/mist, that's affecting the signal cause even in the open I picked up less signals. Rob Quote Link to comment
+MrGigabyte Posted October 7, 2002 Share Posted October 7, 2002 The GPS system was designed such that it is NOT effected by weather. There is a "rain window" about 1.5Ghz and that is one of the reasons GPS is there. There is almost no attenuation even in the heaviest downpour. (Just a db or two). On the other hand, just a few millimeters of standing water will absorb/reflect 1.5Ghz waves. Quote Link to comment
Team Bohica Posted October 7, 2002 Share Posted October 7, 2002 I've been out caching at night in what Texans call a 'frog strangler' on more than one occasion. In a frog strangler you can't see but 10 feet in front of you at night if you're lucky. Makes a 2 star cache into an instant 4+. I'd love to see what someone would say about my being in the middle of nowhere throwing rocks in a flooding creek to make a crossing at 1AM in the morning. Never had a problem getting a signal. My biggest problem is keeping the cache contents and the GPSr dry and fording flooding creeks. I don't care how wet I get of course. Quote Link to comment
Team Bohica Posted October 7, 2002 Share Posted October 7, 2002 I've been out caching at night in what Texans call a 'frog strangler' on more than one occasion. In a frog strangler you can't see but 10 feet in front of you at night if you're lucky. Makes a 2 star cache into an instant 4+. I'd love to see what someone would say about my being in the middle of nowhere throwing rocks in a flooding creek to make a crossing at 1AM in the morning. Never had a problem getting a signal. My biggest problem is keeping the cache contents and the GPSr dry and fording flooding creeks. I don't care how wet I get of course. Quote Link to comment
+RobertM Posted October 7, 2002 Author Share Posted October 7, 2002 Okay, so if rain/mist doesn't affect the incoming signals then perhaps it was the moisture on the GPSr unit? I noticed quite a bit of moisture on my camera and on my clothing. Could the moisture on the GPSr be the cause? Isn't this a bit silly though? Rain/mist doesn't affect the signal but get a film of water between the GPSr and the signal does. So the answer is yes and no? Rob Quote Link to comment
crr003 Posted October 8, 2002 Share Posted October 8, 2002 Nothing better to do at the moment..... One article I found written about ice loading issues – http://www.geomatics.ucalgary.ca/research/GPSRes/Ice.html “The 0.5 inch wet surface ice loading lead to a reduction in SNR of about 3 dB, a raw code horizontal differential position rms error increase of 1 m and a significant increase in the number of cycle slips observed. The 3 dB loss can be explained by the reflection of GPS signals at the air-ice interface in addition to attenuation of the signal transmitted through the ice. A simple model shows that most of this 3 dB loss is due to reflection.” Only a hardcore cacher is going to get 1/2" ice on his antenna! but this helps to explain though why a standing layer of water or ice is more disruptive than a transient/moving effect from rain/mist due to solid reflection rather than scattering. Wet leaves would have more of a reflective effect than dry, as mentioned in earlier posts. Another article is concerned with signal delays due to things in the atmosphere, rather than just signal attenuation – http://www.radiometrics.com/gps_delays.pdf “Dry air, water vapor, hydrometeors and other particulates (sand, dust, aerosols, and volcanic ash) in the atmosphere introduce microwave propagation delays. These delays must be properly characterized to achieve the highest accuracy in surveying and atmospheric sensing using Global Positioning System (GPS) signals. [.....] Depending upon the distribution of precipitation relative to the configuration of GPS satellites, such unmodeled delays can induce horizontal and vertical errors of several centimeters.” Errors of centimeters! Not much to worry about there then. (Assuming you can get a lock on the sats!) When you went back to the area, maybe the satellite geometry was not the same as your first trip, which might not help? What GPS/antenna are you using - it's not a Garmin V is it? Nil Satis Nisi Optimum Quote Link to comment
crr003 Posted October 8, 2002 Share Posted October 8, 2002 Nothing better to do at the moment..... One article I found written about ice loading issues – http://www.geomatics.ucalgary.ca/research/GPSRes/Ice.html “The 0.5 inch wet surface ice loading lead to a reduction in SNR of about 3 dB, a raw code horizontal differential position rms error increase of 1 m and a significant increase in the number of cycle slips observed. The 3 dB loss can be explained by the reflection of GPS signals at the air-ice interface in addition to attenuation of the signal transmitted through the ice. A simple model shows that most of this 3 dB loss is due to reflection.” Only a hardcore cacher is going to get 1/2" ice on his antenna! but this helps to explain though why a standing layer of water or ice is more disruptive than a transient/moving effect from rain/mist due to solid reflection rather than scattering. Wet leaves would have more of a reflective effect than dry, as mentioned in earlier posts. Another article is concerned with signal delays due to things in the atmosphere, rather than just signal attenuation – http://www.radiometrics.com/gps_delays.pdf “Dry air, water vapor, hydrometeors and other particulates (sand, dust, aerosols, and volcanic ash) in the atmosphere introduce microwave propagation delays. These delays must be properly characterized to achieve the highest accuracy in surveying and atmospheric sensing using Global Positioning System (GPS) signals. [.....] Depending upon the distribution of precipitation relative to the configuration of GPS satellites, such unmodeled delays can induce horizontal and vertical errors of several centimeters.” Errors of centimeters! Not much to worry about there then. (Assuming you can get a lock on the sats!) When you went back to the area, maybe the satellite geometry was not the same as your first trip, which might not help? What GPS/antenna are you using - it's not a Garmin V is it? Nil Satis Nisi Optimum Quote Link to comment
+Desert_Warrior Posted October 8, 2002 Share Posted October 8, 2002 In my first post, I mentioned that the efect of any one of the problems is minimal. The real problem is when you are already in a marginal situation. The difference between dry and wet leaves and/or rain/fog/mist might be the difference between a fair lock, or no satellites at all. Having been in radio for 38 years, I am fully aware that 1 or 2 dB isn't much. But in marginal conditions, 1 or 2 dB can be all the difference! I hope to get 2 more dB out of my AO-40 dish at 2401 MHz. 2 here, 1 there, 3 more somewhere else... it all adds up. Mike. KD9KC. El Paso, Texas. Citizens of this land may own guns. Not to threaten their neighbors, but to ensure themselves of liberty and freedom. They are not assault weapons anymore... they are HOMELAND DEFENSE WEAPONS! Quote Link to comment
+raouljan Posted October 8, 2002 Share Posted October 8, 2002 is a 50% loss of power >Personally Responsible for the Recovery of .00217% of the Benchmark Database!<--watch this number! Quote Link to comment
+RobertM Posted October 8, 2002 Author Share Posted October 8, 2002 I'm using a Garmin Legend. Quote Link to comment
crr003 Posted October 9, 2002 Share Posted October 9, 2002 KD9KC, I agree, in a marginal situation you need all you can get. But I think the situation the system is supposed to deal with OK is, assuming you have a lock on some sats, if it starts to rain on you, you shouldn't loose the system? There should be some margin in the link budget to allow for this? And I would hope it's more than 3dB. But I can't find anything definitive about this on the web.(yet). When you think about the additional attenuation caused by the human body blocking signals and tilting the antenna from the optimum receive angle, it's a wonder the thing works at all. Nil Satis Nisi Optimum Quote Link to comment
crr003 Posted October 9, 2002 Share Posted October 9, 2002 KD9KC, I agree, in a marginal situation you need all you can get. But I think the situation the system is supposed to deal with OK is, assuming you have a lock on some sats, if it starts to rain on you, you shouldn't loose the system? There should be some margin in the link budget to allow for this? And I would hope it's more than 3dB. But I can't find anything definitive about this on the web.(yet). When you think about the additional attenuation caused by the human body blocking signals and tilting the antenna from the optimum receive angle, it's a wonder the thing works at all. Nil Satis Nisi Optimum Quote Link to comment
crr003 Posted October 12, 2002 Share Posted October 12, 2002 RobertM, There's some more comments in this thread: another thread Regarding the Legend, some people say the patch antenna is not as good as a quad-helix, but that's a whole other topic. Nil Satis Nisi Optimum Quote Link to comment
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