Does heavy cloud interfere with GPS?

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HC

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Jun 30, 2005, 2:36:25 AM6/30/05
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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 ;-)

Wayne R.

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Jul 1, 2005, 6:24:28 AM7/1/05
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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.

Now, if the moon's not full...

Pieter Litchfield

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Jul 1, 2005, 6:57:58 AM7/1/05
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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.

"HC" <IHat...@home.com> wrote in message
news:42c4...@dnews.tpgi.com.au...

Sam Wormley

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Jul 1, 2005, 8:27:15 AM7/1/05
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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


Don B

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Jul 1, 2005, 11:33:39 AM7/1/05
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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.


HC

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Jul 2, 2005, 12:23:11 AM7/2/05
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Thanks for all the help!

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.

Bronwyn ;-)

H.W. Stockman

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Jul 2, 2005, 6:07:51 AM7/2/05
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"HC" <IHat...@home.com> wrote in message
news:42c6...@dnews.tpgi.com.au...

> Thanks for all the help!
>
> 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.


Dave Patton

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Jul 3, 2005, 1:07:22 PM7/3/05
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"H.W. Stockman" <stockman3@earth-REMOVE_THIS-link.net> wrote in
news:XHtxe.2942$8f7....@newsread1.news.pas.earthlink.net:

> 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.

--
Dave Patton
Canadian Coordinator, Degree Confluence Project
http://www.confluence.org/
My website: http://members.shaw.ca/davepatton/

H.W. Stockman

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Jul 3, 2005, 11:54:11 PM7/3/05
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"Dave Patton" <sp...@trap.invalid> wrote in message
news:Xns968866F9CABD6m...@24.71.223.159...

> "H.W. Stockman" <stockman3@earth-REMOVE_THIS-link.net> wrote in
> news:XHtxe.2942$8f7....@newsread1.news.pas.earthlink.net:
>
> > 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.


Peter

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Jul 4, 2005, 12:22:09 AM7/4/05
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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.

HC

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Jul 4, 2005, 2:52:16 AM7/4/05
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G'day again

Thanks heaps for all the interesting replies.

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


Thanks!!
Bronwyn ;-)

Pieter Litchfield

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Jul 4, 2005, 7:30:56 AM7/4/05
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From my experiences:

(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.

"Peter" <prat...@comcast.net> wrote in message
news:xuOdnbkVhq4...@comcast.com...

DiverHank

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Jul 11, 2005, 6:33:17 PM7/11/05
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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.

Mike Fields

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Jul 12, 2005, 12:23:33 AM7/12/05
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"DiverHank" <dive...@yahoo.com> wrote in message
news:1121121197.6...@g49g2000cwa.googlegroups.com...

> 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.

mikey

Don B

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Jul 12, 2005, 6:25:49 AM7/12/05
to

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.


HC

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Jul 12, 2005, 7:55:33 AM7/12/05
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Actually his GPS was faulty and has been returned for a refund. He has
since bought a BT/GPS.

;-)

pasha

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Sep 10, 2005, 3:15:42 AM9/10/05
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NO

Sam Wormley

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Sep 10, 2005, 3:20:40 AM9/10/05
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pasha wrote:
> NO

David Lee

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Sep 10, 2005, 4:10:17 AM9/10/05
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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.

David


Ray

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Sep 11, 2005, 9:43:06 AM9/11/05
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pasha wrote:
> NO
>
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.

Your mileage may vary.

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