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#1
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Garmin 396 Reception Problems Solved!
Well, as many of you can remember, I have posted my saga about
intermittent reception problems with my Garmin GPSMAP 396 from day one. The Narco Nav/Coms or the splitters that are attached to them appear to be the culprit (both the MK-12D AND Nav 122). I could always select the harmonic freqs that would send the Garmin out to lunch, but it was not a constant problem. Sometimes a freq that would tank the Garmin on one day would be fine the next. This had me doubting the radio stack. I found that minute changes in the antenna position on the glareshield would alter the problem dramatically. Sometimes, moving it 1/4 inch would do it. 8 sats up around 80% to nothing. Zip. Just by moving the antenna a little bit. Even if the thing was only receiving it would tank. Local area ILS freqs would bomb the unit (109.5). Turns out that the default nav freq when you power up the Garmin will lose sat lock. On the ground, it is fine. Take off and climb and the antenna will move a wee bit due to the full throttle and high deck angle. Lost sat reception, but not every time. If the antenna moves just the right way, it will receive although at a MUCH lower signal strength and only 3 or 4 sats. Move it just a touch and it will degrade enough to lose lock, maybe down to 0 strength on all sats. I first thought that the problem of lost sat lock was due to LOW signal strength and switched to a higher gain antenna. Switching to the higher gain antenna actually made the problems worse. With it, many more radio freqs tank the Garmin. Both on COM transmit and NAV receive. It appears that mounting the antenna up high on the windshield may be the permanent cure. I cannot justify the ridiculous cost of an external antenna. $300- $400 for a twenty buck antenna is nuts. I'll report back if this does the trick. Anyone know of a nifty little "shelf" I can mount in the Cherokee up high? Maybe something sliding into the windshield trim plastic? Mike |
#2
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Garmin 396 Reception Problems Solved!
I'd be happy to sell you a Garmin GA56 remote antenna. It is in excellent
condition. They were used with the straight Garmin GNS-430. When I upgraded to the 430W, it came with a different antenna. $68.....free shipping in the US. Karl "curator" "Mike Spera" wrote in message ... Well, as many of you can remember, I have posted my saga about intermittent reception problems with my Garmin GPSMAP 396 from day one. The Narco Nav/Coms or the splitters that are attached to them appear to be the culprit (both the MK-12D AND Nav 122). I could always select the harmonic freqs that would send the Garmin out to lunch, but it was not a constant problem. Sometimes a freq that would tank the Garmin on one day would be fine the next. This had me doubting the radio stack. I found that minute changes in the antenna position on the glareshield would alter the problem dramatically. Sometimes, moving it 1/4 inch would do it. 8 sats up around 80% to nothing. Zip. Just by moving the antenna a little bit. Even if the thing was only receiving it would tank. Local area ILS freqs would bomb the unit (109.5). Turns out that the default nav freq when you power up the Garmin will lose sat lock. On the ground, it is fine. Take off and climb and the antenna will move a wee bit due to the full throttle and high deck angle. Lost sat reception, but not every time. If the antenna moves just the right way, it will receive although at a MUCH lower signal strength and only 3 or 4 sats. Move it just a touch and it will degrade enough to lose lock, maybe down to 0 strength on all sats. I first thought that the problem of lost sat lock was due to LOW signal strength and switched to a higher gain antenna. Switching to the higher gain antenna actually made the problems worse. With it, many more radio freqs tank the Garmin. Both on COM transmit and NAV receive. It appears that mounting the antenna up high on the windshield may be the permanent cure. I cannot justify the ridiculous cost of an external antenna. $300- $400 for a twenty buck antenna is nuts. I'll report back if this does the trick. Anyone know of a nifty little "shelf" I can mount in the Cherokee up high? Maybe something sliding into the windshield trim plastic? Mike |
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Garmin 396 Reception Problems Solved!
I had that exact same problem with my new 496. On my BFR we did a
couple of ILS approaches as the last thing we did. Since I never use my nav radios otherwise the frequency was left on the last localizer we used. Then I noticed the GPS wouldn't work. It would work until I started the plane then absolutely nothing. As soon as you shut the plane down the GPS fires up with 12 satellites. This went on for one week. I took the 496 to the avionics shop. The owner of the shop came out to the plane with me with another 496. In 5 minutes we figured out the problem. As soon as we shut off the Mk12D with the localizer frequency the GPS's worked. Turn it back on and both GPS's failed. Switch nav freq's and it works again. So we know it's in the one radio on the nav side and only on certain freq's. I rerouted the external antenna to the pilots side of the glare shield and this solves the problem too. The panel mount GPS sits right on top of this radio and is unaffected. The LOC freq that gave me trouble was 111.5. The other LOC on 110.3 doesn't cause any problems. Mike Spera wrote: Well, as many of you can remember, I have posted my saga about intermittent reception problems with my Garmin GPSMAP 396 from day one. The Narco Nav/Coms or the splitters that are attached to them appear to be the culprit (both the MK-12D AND Nav 122). I could always select the harmonic freqs that would send the Garmin out to lunch, but it was not a constant problem. Sometimes a freq that would tank the Garmin on one day would be fine the next. This had me doubting the radio stack. |
#4
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Garmin 396 Reception Problems Solved!
On Sep 19, 9:27 am, Newps wrote:
... The LOC freq that gave me trouble was 111.5. This is a common problem with the 12D. see this previous post: http://tinyurl.com/342cbu |
#5
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Garmin 396 Reception Problems Solved!
On Sep 19, 5:33 pm, mikem wrote:
On Sep 19, 9:27 am, Newps wrote: ... The LOC freq that gave me trouble was 111.5. This is a common problem with the 12D. see this previous post:http://tinyurl.com/342cbu Follow up: In the old thread, Fong posted that the LO injection on the 12D is low-side, and the first IF is 17MHz. That puts the LO at 115.5-17=98.5. The sixteenth harmonic of 98.5 is 1576MHz, which apparently blocks the GPS. |
#6
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Garmin 396 Reception Problems Solved!
On Tue, 18 Sep 2007 18:06:25 -0500, Mike Spera
wrote: Well, as many of you can remember, I have posted my saga about intermittent reception problems with my Garmin GPSMAP 396 from day one. 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. Last modified on: 08/30/2007 " |
#7
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Garmin 396 Reception Problems Solved!
On Tue, 18 Sep 2007 18:06:25 -0500, Mike Spera
wrote: Well, as many of you can remember, I have posted my saga about intermittent reception problems with my Garmin GPSMAP 396 from day one. The Narco Nav/Coms or the splitters that are attached to them appear to be the culprit (both the MK-12D AND Nav 122). I could always select the harmonic freqs that would send the Garmin out to lunch, but it was not a constant problem. Sometimes a freq that would tank the Garmin on one day would be fine the next. This had me doubting the radio stack. I found that minute changes in the antenna position on the glareshield would alter the problem dramatically. Sometimes, moving it 1/4 inch would do it. 8 sats up around 80% to nothing. Zip. Just by moving the antenna a little bit. Even if the thing was only receiving it would tank. Local area ILS freqs would bomb the unit (109.5). Turns out that the default nav freq when you power up the Garmin will lose sat lock. On the ground, it is fine. Take off and climb and the antenna will move a wee bit due to the full throttle and high deck angle. Lost sat reception, but not every time. If the antenna moves just the right way, it will receive although at a MUCH lower signal strength and only 3 or 4 sats. Move it just a touch and it will degrade enough to lose lock, maybe down to 0 strength on all sats. I first thought that the problem of lost sat lock was due to LOW signal strength and switched to a higher gain antenna. Switching to the higher gain antenna actually made the problems worse. With it, many more radio freqs tank the Garmin. Both on COM transmit and NAV receive. It appears that mounting the antenna up high on the windshield may be the permanent cure. I cannot justify the ridiculous cost of an external antenna. $300- $400 for a twenty buck antenna is nuts. I'll report back if this does the trick. Anyone know of a nifty little "shelf" I can mount in the Cherokee up high? Maybe something sliding into the windshield trim plastic? Mike We had a similar problem with a Skyforce II GPS which failed when some NAV frequencies were selected. Checking the satellite signal strength, on the GPS, confirmed it dropped to zero when the NAV receiver was tuned to some frequencies. The GPS receiver was being blocked. Whilst we do have Narco MK12D+ that was not the problem. The DME (Narco IDME 891) is slaved to the NAV so the fault would clear when the DME was turned off. The fault was cleared by fitting an external GPS antenna but before blaming the DME it should be noted that the Skyforce II GPS was the problem. It is an old design and the receiver is not as good as the replacement Skyforce IIIc which works very well. |
#8
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Garmin 396 Reception Problems Solved!
I'll report back if this does the trick. Anyone know of a nifty little "shelf" I can mount in the Cherokee up high? Maybe something sliding into the windshield trim plastic? Mike I used velcro to secure the antenna to the upper left corner of the plastic sun visor, then ran the wire down inside the window trim. |
#9
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Garmin 396 Reception Problems Solved!
Paul kgyy wrote:
I'll report back if this does the trick. Anyone know of a nifty little "shelf" I can mount in the Cherokee up high? Maybe something sliding into the windshield trim plastic? Mike I used velcro to secure the antenna to the upper left corner of the plastic sun visor, then ran the wire down inside the window trim. O.K. Great idea. 99% of the time, the visor is stowed in the "up" position. I can mount it on top of the visor in a way that swinging the visor down just inverts the antenna. Will it work inverted, or sideways? Thanks, Mike |
#10
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Garmin 396 Reception Problems Solved!
Mike Spera wrote:
Paul kgyy wrote: I'll report back if this does the trick. Anyone know of a nifty little "shelf" I can mount in the Cherokee up high? Maybe something sliding into the windshield trim plastic? Mike I used velcro to secure the antenna to the upper left corner of the plastic sun visor, then ran the wire down inside the window trim. O.K. Great idea. 99% of the time, the visor is stowed in the "up" position. I can mount it on top of the visor in a way that swinging the visor down just inverts the antenna. Will it work inverted, or sideways? Thanks, Mike Probably not. The antenna is a patch antenna backed up by a metal ground plane. If you turn it upside down it will not be facing the satellites, so if it works at all your signals will be very weak. Sideways it might be OK if the satellite is visible from that side of the airplane. |
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