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GPS Satellite Reception Dropout

rv7boy

rv7boy

Forum Peruser
A good friend and fellow pilot (RV-9A) and I both bought 396's at Oshkosh in 2006. And we both have had similar problems...occasionally the GPS just quits, with a message that says something like "Lost Satellite Reception." I have noticed that mine always drops out on the way to my favorite grass airport, Moontown, 3M5, near Huntsville, Alabama.

I mentioned this to Paul Dye a few months ago who is also using a Garmin 396 with XM Weather. He said his always drops out near a certain "antenna farm" near Houston.

Hmmm....looking at my usual trip to Moontown through Huntsville (HSV) Class C airspace, I notice that I travel BETWEEN two hilltops with lots of TV and RADIO ANTENNAs on top of them. This last Saturday I also had the dropout on the way to Moontown, but on the way back I avoided going between the hills and chose rather to go around them on the north side, and I had continuous satellite coverage. More hmmm...

My friend is more frustrated than I am as his 396 refused to acquire satellites during a 30 minute flight around the local airport (DCU) last Saturday. We both have updated the software from the web site and I believe we are operating the latest version.

So the question is "Is anyone else having similar problems with their 396 (or 496's)?"

If there is a preponderance of such satellite reception dropouts across the country, I am wondering if we could have a map of "thumbpins" showing where they are. More importantly, I am wondering if Garmin has a problem that has been reported by many of us but has not fixed the problem. I also recently had a momentary dropout near Dayton, Ohio, so I am beginning to suspect my 396 may not be as reliable as I thought it was.

My friend is planning to call Garmin and expects to send his 396 back to them for a thorough checkout. I'm not ready to do that yet.

Also, do Lowrance or other brands of handheld GPS's have the same occurrence?

Obviously, my friend and I should do a side-by-side test on the Moontown trip but he is so aggravated that he is ready to send his back to Garmin.

Any similar experiences out there?

Don
 
Garmin only, or general GPS problem?

Don, I am sorry to hear that you have these problems. However, to me this is very strange.

Imagine, I use a GPS in my Lexus for more than 6 years now (back than GPS?s were not as sophisticated as they should be now!) In all this time of driving around a very congested Europe (Belgium, Holland, Germany, UK, Austria, Switzerland, etc.) with lots of industry, antennas and the like, I have not had one ?lost satellites? message or anything similar, ever, unless I was in an underground parking or a tunnel (but the moving map in the Lexus still keeps working on memory and input from the steering and the wheels), really.?. not ones, even between the mountains of Austria, or in a build up city like Frankfurt!

I use an Avmap EKP-IV for flying (so far as a knee-pad moving map in C-152/172,s), again never had any ?lost satellites? messages. In an other thread I mentioned that I tested the EKP-IV in my car trying to hide the antenna under my seat, but it still kept on going!

If the Garmin is skipping, is it because some of the satellites were out of order at the time? Or is it really only in certain spots, as you describe? What sort of signal could mess-up the GPS-reception?

I am really interested to hear what the problem is and if it could upset any GPS or if it is only a Garmin problem. Keep us posted.

Regards, PilotTonny
 
Thanks for your reply, Tonny.

I usually try to do an internet search before posting, but with a feeling of trying to help my friend as well as share my experiences, I went ahead and published my original post.

I just now did a Google search, and found the following. This is interesting reading and is even cause for more alarm, as it indicates some RF interference can originate from onboard avionics. As one poster on another group said, a 396 should be able to do handstands!

Here's one post I clipped from another discussion group. It sounds like the answer is from Garmin. Sure makes me wonder why a panel mount like a 430 doesn't have this problem. Maybe I need to go to an external antenna.
Here's the post and answer I found:

<SNIP>...
"The same reason my 196 loses reception, from Garmin's support database

"
Question: Why is my GPS losing satellites in the middle of my flight?
Answer:


Portable GPS units have the ability to experience loss of satellite
reception as a result of RF interference caused by a variety of
sources. These sources can be as simple as a portable MP3 Player used
for in flight entertainment to a ground based air traffic control
radar antenna on an airport. When these devices are powered on and are
in close proximity to the portable GPS or antenna, the GPS may lose
satellite acquisition as a result. Another common source of RF
interference is aircraft communication and navigation radios. When
certain radios are tuned to a specific frequency there is the
potential for enough RF interference to be released that the Portable
GPS unit will experience loss of satellite reception as though the
signals were being jammed. An article in the Aviation Consumer, dated
February 15th, 1994 has outlined a list of aviation communication
radios and frequencies that may cause a portable GPS unit to lose
satellite reception in the aircraft. This information is listed below.


Radio Frequencies That May Jam GPS Receivers.


Transmit 131.285 and 121.186 Receive


Narco MK 12D/E Com 810/811, Nav 824/825 Com 131.220 and 119.285 Nav
115.464 and 109.672


King KX 155/165 Com 131.820 and 119.885 Nav 116.128 and 109.564


King KX 170/175 Com 122.285 and 130.186 Nav 113.651


Collins Microline Com 132.720 and 120.785 Microline Nav 116.028 and
109.464


Notes: KX 155/165 transmitting on 118.15 ws shown to jam an external
mounted antenna. Narco MK 16 tuned to any 115 or 109 Nav channel was
shown to jam a hand held GPS. Narco MK 12D/E and Nav 824/825, if not
wired with memory keep alive, will default to 115.5 MHz in the active
channel and will jam any GPS receiver. "...<SNIP>

Don
 
Info.

My 496 seems to work as expected.
My friend just sent his 396 back for a warranty repair.
He could only get one sat. even after changing the antenna, yet his GX60 was working just fine. He call Garmin and was told to send it in for a free repair.

Kent
 
Pilottonny said:
Don, I am sorry to hear that you have these problems. However, to me this is very strange.

Imagine, I use a GPS in my Lexus for more than 6 years now (back than GPS?s were not as sophisticated as they should be now!) In all this time of driving around a very congested Europe (Belgium, Holland, Germany, UK, Austria, Switzerland, etc.) with lots of industry, antennas and the like, I have not had one ?lost satellites? message or anything similar...
Click to expand...
I would expect electronics in airplanes to be more susceptible to interference from transmitters on towers than automobiles on the ground. The antenna is usually up high on the tower and has gain such that the strong part of the signal would tend to shoot over a ground vehicle that is near the antenna. That same gain might shoot right at an aircraft, especially at lower altitudes.
 
I can't see where one brand/type of GPS should be more or less affected than another, BUT I have had no dropouts in over 100 hours flying my RV with and AvMap IV, nor ever with it in other aircraft before finishing the 9A. I did have dropouts with a 196 in a Cessna 180 and the owner said to just switch off the alternator for a moment and it would come back. Very strange. There are things we aren't meant to understand...

Bob Kelly
 
Antennae

If you are using the 396/496 with it's built in antenna, you might experience much better reception with an external amplified antenna.

There is no gain in the attached antenna. One of the non-WAAS antennae being removed from 430/530 installations that are being upgraded might improve things. These GA-56 antennae are amplified.

In general, bigger is better for antennae...:) ...and if you can't make it bigger, add gain....:)

gil A
 
GPS Question to Dan Checkoway

Dan,
I hope you are following this thread. I'd be interested in knowing if you ever have any "Lost Satellite Reception" messages with your antennas mounted below the fiberglass panels you fabricated.
Thanks,
Don
 
az_gila said:
If you are using the 396/496 with it's built in antenna, you might experience much better reception with an external amplified antenna.

There is no gain in the attached antenna. One of the non-WAAS antennae being removed from 430/530 installations that are being upgraded might improve things. These GA-56 antennae are amplified.

In general, bigger is better for antennae...:) ...and if you can't make it bigger, add gain....:)

gil A
Click to expand...

Thanks for the reply, Gil. I'm not using the attached antenna but rather the one that has the length of cable for mounting on the glareshield. I have it velcroed in place.

I notice the GA-56 lists for $385 but is available for $100 on ebay. I'm still interested in using what Garmin supplied with my GPS.

Don
 
Deep South Mystery

Hmmm... My wife and I were on vacation week before last, driving on the interstate between Mobile and Montgomery, Alabama. My PDA based road nav system dropped out several times. The drops were around 10 minutes at freeway speeds. I noticed the satellite reception signal LED on the receiver was not showing a singnal.
 
Amplified or not?

rv7boy said:
Thanks for the reply, Gil. I'm not using the attached antenna but rather the one that has the length of cable for mounting on the glareshield. I have it velcroed in place.

I notice the GA-56 lists for $385 but is available for $100 on ebay. I'm still interested in using what Garmin supplied with my GPS.

Don
Click to expand...


Don,

Is it an amplified antenna? ... or just a remote mount for the standard, non-amplified one?

BTW.. the GA-56 antennae are now $35 (shipping included) via VAF...:)

http://www.vansairforce.com/community/showthread.php?t=22739

gil A - more dB gain is better....
 
Another possible solution...

I got a private email from a 396 user who said the only time he had a problem was when he was using the little antenna on the cord (that's the same one I use) and that was when it was located close to the GPS-18 "hockey puck" receiver/antenna. Also, certain known RF sources like antenna farms aggravated the problem.
Just continuing the thread, hoping this has an easy solution...
Don
 
Last edited:
jsherblon said:
Hmmm... My wife and I were on vacation week before last, driving on the interstate between Mobile and Montgomery, Alabama. My PDA based road nav system dropped out several times. The drops were around 10 minutes at freeway speeds. I noticed the satellite reception signal LED on the receiver was not showing a singnal.
Click to expand...

No problem with your GPS.....that stretch of I-65 is so far out in the sticks that CD players won't work...... ;)

Time seems to stand still on that part of the drive to Mobile to see the kid.... :)

I can't comment on the Garmin units, but my Lowrance Airmap 1000 with glare shield-mounted antenna has been solid with no reception problems.
 
Last edited:
496 problems too

Last Saturday at 11:00 a.m. we flew 20 minutes to an airshow and my 496 with the remote antenna absolutely refused to acquire satellites. After it sat in the warm sun for 5 hours it acquired them in minutes. This is the third time in three months it has done this. I dunno...I've taken the battery out for a couple of minutes, turned it off and waited then turned it back on????????
 
From Garmin

I have the same drop out on my 396 every once in awhile on long trips. Their response:
Thank you for contacting Garmin International, The GA 26 antenna tends to be very reliable. At this point, I would start with troubleshooting software/almanac issues that could be causingthis. If you think it might be the antenna, re-install the stub antennaand use the procedures listed below to correct any software/almanac issues. The first resets the satellite almanac data, the next resets the entire unit (erasing all user data), and the last re-installs the operating system from our website. Try each one to see if it resolves the issue. ********************Satellite Reset - With the unit off, press and hold the Zoom OUT button while turning the unit on. This will reset the satellite data. ********************(Before doing any of the procedures listed below, you may want to backupyour user data - waypoints, routes, tracks - as it is usually erased during the following procedures. This is easily done if you have one ofour computer Mapsource software products. It can then be reloaded later.) Master Reset - With the unit off and all cables disconnected and any datacard removed, press and hold the OUT+QUIT+NRST buttons. Tap the POWER button once for about .5 - 1 second. (The unit will beep and power up to a shaded screen.) Continue holding the OUT+QUIT+NRST buttons for about 6 - 8 seconds and then release. If the unit powers off or refuses to power up to full brightness, remove and re-install thebattery and perform this reset procedure only one more time. Again remove and re-install the battery. The unit should now function properly. After this is done, enable the WAAS function and take it outside to let it acquire the satellite signals for about 10 minutes. ********************Unit Software Update - To do the Unit Software update, remove any datacard (if installed) and follow the steps below. Make sure to read all warnings as this update may erase all routes, waypoints, and tracks in the unit. 1. Go to our website at http://www.garmin.com/support/agree.jsp?id=921.2. Follow this link through the download process. 3. Save the file in a location on your computer that can be easily found- I suggest the Desktop.4. Find the downloaded file on your computer and run it (double click). 5. Select USB if that is how the GPS is connected to the computer.6. Make sure the GPS is turned on - simulator on. This update may take a minute to complete. After this is done, enable the WAAS function and take it outside to let it acquire the satellite signals for about 10 minutes.
 
Cell phone interference

I was having the same issues with my 496 using the Garmin issued remote antenna. It seemed to happen to me when I was near Mt Wilson in SoCal which is an antenna farm for all the local TV guys. But it happened again in the middle of the San Joaquin Valley as well. I would switch to the little
antenna attached to the 496 and everything returned to normal. This happened on at least 4 occasions. I installed the latest software update (ver 3.30) and I made sure my (AT&T) cell phone is off, no more issues.
Which one fixed my problem? Don't know.
 
Possible Fix

This is from a friend with a Mooney and a 396:

"...the first several thousand 396's had defective antennas. I paid 100 because I didnt want to wait, but if they google the 396, they will find the info reqd to get a new one free from garmin. since i put in my new antenna, i have never lost sat recept."
 
Defective Antenna

I too had the earlier antenna. But with the replacement the 396 dropped signal 3 times on a recent trip to the midwest from CA after months of perfect service. Tonight it dropped signal then couldn't find the sattelites for 20 minutes. I'll be trying their reset information posted earlier. Will post results if it's useful to you all.
 
Voice of America?

Chino Tom said:
I was having the same issues with my 496 using the Garmin issued remote antenna. It seemed to happen to me when I was near Mt Wilson in SoCal which is an antenna farm for all the local TV guys. But it happened again in the middle of the San Joaquin Valley as well. I would switch to the little
antenna attached to the 496 and everything returned to normal. This happened on at least 4 occasions. I installed the latest software update (ver 3.30) and I made sure my (AT&T) cell phone is off, no more issues.
Which one fixed my problem? Don't know.
Click to expand...

Tom... if you lost signal in the Central Valley near Delano, you can blame the VOA SW transmitter station there... lots of RF energy radiating around...:)

My sailplane electronic variometer wouldn't work in the area, the only place that has happened...

But the problem will go away the end of this month....

http://www.rwonline.com/pages/s.0100/t.7486.html

gil A
 
GA-25 antenna should be replaced by GA-26 antenna

hevansrv7a said:
This is from a friend with a Mooney and a 396:

"...the first several thousand 396's had defective antennas. I paid 100 because I didnt want to wait, but if they google the 396, they will find the info reqd to get a new one free from garmin. since i put in my new antenna, i have never lost sat recept."
Click to expand...

I received a pm suggesting I check my antenna model number. I found out I have the GA-25 antenna which gave a lot of service problems. I plan to contact Garmin tomorrow to see about getting the newer GA-26. Since it appears to be an antenna problem, I have a few tests in mind as soon as we get some good flying weather here in North Alabama.

My friend's 396, however, seems to have a worse problem. I will direct him to the Garmin reset procedures provided above. Thanks to everyone. I don't have my problem fixed yet, but at least I don't feel alone anymore.:eek:

Don
 
Sam Buchanan said:
<SNIP>
I can't comment on the Garmin units, but my Lowrance Airmap 1000 with glare shield-mounted antenna has been solid with no reception problems.
Click to expand...

But Sam, I've never seen you fly through the "Valley of RF" over near Chapman Mountain. Your dawn patrol always seems to fly around Huntsville's Class C instead of through it. ;)

I'd be interested if your Lowrance has any reception problems going on a nearly straight line from DCU to just north of Moontown. It always happens just before leaving the Class C and tracking apx. 060 degrees between the two "mountains" populated with the TV and radio broadcast towers. I usually fly at 2500 MSL.

I also wonder if any of the other local (DCU and HSV) pilots have had similar problems in that area.

My unit's problems could very well be due to the Garmin GA-25 antenna so I plan to replace it with the newer GA-26.

Don
 
Last edited:
But Sam, I've never seen you fly through the "Valley of RF" over near Chapman Mountain. Your dawn patrol always seems to fly around Huntsville's Class C instead of through it.
Click to expand...

Don, I've returned to DCU from Moontown using that route and don't recall any GPS reception problems. Sometimes I'll cut through HSV airspace to make sure the transponder is still working. :)

The only time I've seen a GPS dropout was when I was flying the old Lowrance Airmap 100. When I installed the Garmin GPS35 receiver (a rock-solid receiver used for driving the iPAQ with AnywhereMap) on the glareshield next to the Airmap antenna, sometimes the Lowrance unit didn't want to play nice with the Garmin. But the Airmap 1000 has never had any problems with the GPS35 running next to it.
 
That's a good data point, Sam. I knew you would reply. I contacted Garmin Tech Support this morning and they explained to me that the GA-25 antenna I have is indeed a more sensitive antenna and is thus more sensitive to RF transmissions from TV, radio and cellphone towers as well as VOR stations. The GA-26 is being sent free, and I will report if I continue to have problems as...

"Yea, though I fly through the Valley of RF..." :rolleyes:

Aviation is indeed a continuing education.

Don
 
I have the same problem with my 396. The "LOST SATELLITE RECEPTION" zone is about 4 miles NE of my home airport of Henderson, KY (KEHR). It happens every time I fly through there. It has also happened a couple other times while flying cross-country. It usually doesn't last long but is still very irritating.
 
Garmin Antenna Status Report

I thought I would give a little status report for the file archives.

As I posted earlier, I contacted Garmin Technical Support last Wednesday, explaining my problems, and they agreed to send a GA-26 antenna. It arrived two days later via UPS no charge. I haven't flown with it yet, but plan to soon.

Also, my friend contacted Garmin Technical Support last Thursday, and they walked him through the complete reset procedure. He hasn't had a chance to fly it yet, but on a 450 mile round-trip automobile venture last weekend, he said it acquired satellites every time he tried...about 6 times. So he feels confident his problem is solved.

We both are very complimentary of Garmin's Technical Support. They are very courteous and understanding of dorks like me who tend to get bumfuzzled with electrons and electronic gadgets. Give me a button and I can push it, but don't ask me to explain what's going on underneath the button! :eek:

I plan to fly my new GPS-26 antenna this week and will (hopefully) be able to conclude this thread.

Don
 
Hi,

I had a similar problem in my 172. I fixed it by installing an external antenna. No dropouts after the install.
 
Update

Well, I have the new antenna and had the 'lost satellite signal' warning several times during the trip to Memphis and back. I posted the resetting instructions I got and tried the first two which includes a master reset where you lose all your settings and have to put them all back in. I had already downloaded the latest software a few weeks ago. Went flying over northern Cal and on the way back lost satellites again for about 5 minutes. It only sees a couple very weakly and took a long time to come back to life. Will send this feedback to Garmin. They have been very helpful with this and other issues but this one is getting old.......:(
Dave
 
Interesting thread...

I made two round trips last weekend from Minneapolis to Ames, IA (about 190 n.m. each way), and I noticed that my Anywhere Map unit was going in and out of 3D mode, with a few complete dropouts. It probably happened 25 times or more yesterday. I don't recall ever seeing any dropouts before, but, I also was using it as my primary navigation instrument, so I was looking more often at it. (The horrors of what would have happened if I didn't have any GPS - Oh, noooo :eek:)

Unfortunately, my 430 is out for the upgrade, so I couldn't compare. But, I've run the Anywhere Map for over three years, and don't recall ever seeing this. It could be the gps unit, of course, time will tell. There is this Notam, which is not supposed to affect us "down low" guys, but it is interesting:

"Minneapolis Center (Farmington MN) [ZMP]: April NOTAM #35 issued by Gps Notam OA [GPS]
Non CIVILIAN GPS May be unreliable or unavailable within a 240 nautical miles radius of 420153N/913847W at FL400 effective from April 24th, 2007 at 07:01 PM CDT (0704250001) - December 31st, 2007 at 06:59 PM CDT (0712312359)"

Wonder what that is all about? The point described is just east of Cedar Rapids, IA.
 
SAASM Testing

AlexPeterson said:
.....
"Minneapolis Center (Farmington MN) [ZMP]: April NOTAM #35 issued by Gps Notam OA [GPS]
Non CIVILIAN GPS May be unreliable or unavailable within a 240 nautical miles radius of 420153N/913847W at FL400 effective from April 24th, 2007 at 07:01 PM CDT (0704250001) - December 31st, 2007 at 06:59 PM CDT (0712312359)"

Wonder what that is all about? The point described is just east of Cedar Rapids, IA.
Click to expand...

Collins Radio is there.....;)

Testing of the SAASM has to occur somewhere....:)

...old press release here, but you can get the point....

http://www.rockwellcollins.com/news/page2905.html

gil A
 
FWIW,
Sounds like you have the problem figured out, but wanted to share my experience with my 396.

I experienced loss of sat reception on the way back from Branson a few weeks ago. Just couldn't get it to lock on like it always had. I was using the extended antenna and had it mounted on top of the glareshield in front of the roll bar brace. (6A Slider).

A few days later, just messing around, I moved the antenna placement around the glareshield and immediately got a good lock on more sats than ever before.

To date, there have been no more problems.

Funny though, as soon as we got back home that afternoon, the sat tv went off at the house. Clear day, no clouds. There was a message that came up on the screen that indicated the sat reception was not reliable because of sun spot problems. That is the only day it has occured so it must not be too widespread.

I figured that the antenna placement was the problem since I haven't had any more problems. You might try different locations on the glare screen and see if it makes any difference.
 
GA-26 Antenna seems to be the answer!

Well, they taught us in school to not draw conclusions from one data point, but I can report here that I flew for an hour today with no "lost satellite reception" message. I flew through the "Valley of RF" on the way to Moontown and the reception was rock solid.

So, I feel my problem is solved, and I really appreciate everyone offering their suggestions and information.

And thanks, Gil, for the info about the special price on the GA-56. My friend and I each bought one and may decide to use them later.

Thanks everybody! :D

Don
 
Long Live the 295

With all the problems you-all are having with the 300 and 400 Garmins, I'm glad I did not abandon the trusty old 295. It works very well, usually with 5 or 6 satellites, has never failed me except once when I overloaded the processor by changing pages too quick and it locked up - switched it off and on and it was back to normal pronto.

But I must admit though, I am tempted. It would be nice to have XM weather and music.

dd
 
Another thing to consider

A while back I was storm chasing with my Garmin 496 in the car. I was using the attached stick antenna with the 496 up on the dash. A friend had another GPS attached to a laptop. It was an integrated GPS and antenna that he threw up by my Garmin. I noticed that I started losing lock. Through experimentation I found that the distance between his GPS/antenna and mine had a striking effect on my received signal levels. If the antennas were close I would lose some satellites completely and others would be greatly attenuated. If the antennas were a foot or so apart, all was well.
 
Signal loss

I use a GRT EFIS internal with WAAS and it never drops out. I also have a Lowrance 2000C with amplified external mounted on the glarescreen next to the GRT ant and when using WAAS it frequently looses signal :( but immediately regains it when I turn off WAAS. This happens to me all over the front range of Colorado. Annoying, to say the least.

Dennis Mitchell
RV6A
 
Ant spacing

Larry, I didn't read your post before my own. Interesting about antenna location. I will try moving mine on the next flight and see what happens. Perhaps they are too close at three inches between.
 
Lowrance drop out

Yes Lowrance has a drop out or lost signal problem too. I have had three of them in the past 12 months. At first I thought I had a bad GPS. This is not the case. I am convinced that the lost signal is a radio interference problem of some kind. It happens to me from 14 miles East of Yuma AZ and sometime 10 miles North of Yuma AZ. I have lost signal for as long as 30 minutes in the local area too. We have a lot of military radio stuff here as well as civilian radio stations. Something in the mix causes this problem. Lowrance does not have an answer to this issue. I am willing to bet that Garmin will have the same answer.

Tom
 
Need to know...

Sky Harbor Tom said:
Yes Lowrance has a drop out or lost signal problem too. I have had three of them in the past 12 months. At first I thought I had a bad GPS. This is not the case. I am convinced that the lost signal is a radio interference problem of some kind. It happens to me from 14 miles East of Yuma AZ and sometime 10 miles North of Yuma AZ. I have lost signal for as long as 30 minutes in the local area too. We have a lot of military radio stuff here as well as civilian radio stations. Something in the mix causes this problem. Lowrance does not have an answer to this issue. I am willing to bet that Garmin will have the same answer.

Tom
Click to expand...

Tom... I would hazard a guess that the answer would be clasified.

Yuma Proving Ground is testing the latest smart munitions...

http://www.globalsecurity.org/military/systems/munitions/m982-155.htm

Part of all these systems is a SASSM approach that needs testing....

http://www.acronymfinder.com/af-query.asp?acronym=SASSM

gil A
 
Sky Harbor Tom said:
I am convinced that the lost signal is a radio interference problem of some kind. It happens to me from 14 miles East of Yuma AZ and sometime 10 miles North of Yuma AZ. I have lost signal for as long as 30 minutes in the local area too. We have a lot of military radio stuff here as well as civilian radio stations. Something in the mix causes this problem.
Click to expand...
It is quite likely that there is a local source of the interference. It seems that there are many different things that can cause interference with GPS signals. One day I was doing a proficiency flight with an inspector from Nav Canada. We discovered a repeatable loss of GPS signal NE of CYHM. While discussing this, he mentioned that he had participated in an investigation of another repeatable GPS interference problem that proved to be caused by the television receiver on a boat in a marina. Go figure.

Moral of the story - don't rely on GPS as the sole source of navigation info. If you are VFR, be prepared to use a map. If you are IFR, have another available source of nav info.
 
Kevin Horton said:
One day I was doing a proficiency flight with an inspector from Nav Canada. We discovered a repeatable loss of GPS signal NE of CYHM. While discussing this, he mentioned that he had participated in an investigation of another repeatable GPS interference problem that proved to be caused by the television receiver on a boat in a marina. Go figure.
Click to expand...
quite possibly he was referring to a case very similar to the infamous Moss Landing (California) Harbor case back in 2001, very well documented here:

http://www.gpsworld.com/gpsworld/article/articleDetail.jsp?id=43404

I also found an interesting Powerpoint deck from the 46th Test Squadron of the USAF talking about interference to the GPS signal here:

http://www.navcen.uscg.gov/cgsic/meetings/EISubcommittee/2005_presentations/06 Vulner PRA.ppt

Ciao, Luca
 
I have a Garmin 430W and a 396 in my Piper. I started having the same problem since I upgraded my 430 to waas. I called the avionics shop and talked to them about it. He said bring it over tomorrow if possible. When I arrived at the shop he walked out and asked what com freq I was on when this happened. I was a little stumped at first but we started trying freqs. that I was on the last time I noticed it. Dialed up 121.00 Cincinatti approach hit my transmit button and got the messages lost satellite. I was shocked. Turned to 121.65 satellite same thing. It turns out that my ELT on 121.5 effects both 430 and 396. We unhooked ELT and the problem went away. We swapped out my elt for another elt from another piper and no problem. Something with my elt. The shop had researched this before I got there and this was from Garmin. My com 1 is my 430 and my #2 radio does it also. The 396 seems to take a little longer to go down. It happens when you transmit on any freq on 121.xx. I ordered a new ELT.

RV-10 QB in progress
 
B737NG said:
Does anyone ever check the raim predictions for your route of flight?

I just found this handy website: http://raimprediction.net/ac90-100/
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I haven't used a program to do the RAIM prediction before flight, but I've done hundreds of RAIM predictions using on board GPS systems. In my experience, there is very poor correlation between the RAIM prediction and whether you will or will not actually have RAIM at the FAF. I've had many cases where the RAIM prediction said there would be a RAIM problem, but we continued with GPS as the weather was VMC, only to find that we did have good RAIM at the FAF. I've had many other cases where the RAIM prediction said everything was OK, yet we did not have RAIM at the FAF.

The RAIM prediction algorithms look at where the satellites will be when you reach the FAF, and see if there will be enough satellites, with good geometry (i.e. the available satellites cannot all be in one area of the sky). The prediction does not use satellites that will be low on the horizon, as it is assumed that your antenna might not be able to pick them up. But, in fact, the GPS antenna usually does receive the satellites that are low on the horizon, so the actual number of satellites available would be higher than predicted, which allows the GPS to have RAIM when it was predicted to not be available.

I believe that many cases of no RAIM at the FAF are due to something interfering with the GPS signals, and this interference cannot be predicted by the RAIM prediction program.
 
Different issue?

My soal navigation instruement is a Garmin 496 and I have had issues with it twice, in almost the same location.

Both times were on flights from 3M3 (Collagedale, TN) to 28A (Goose Creek - Charlotte, NC) at 9,500'.

The first instance the GPS just locked up. Turning it off and back on again reset it.

On the second instance I was 60 miles from CLT's Class B airspace and when the GPS updated the image it stopped drawing the Class B upside down wedding cake but remained functional. Once again, turning it off and back on solved this problem.

Have any of you had similar issues with a G496?
 
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