Can a TV aerial interfere with a GPS signal?

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I've owned my present boat 3 yrs and have occasionally suffered loss of GPS fix for both plotters onboard, providing me with a few bottom clenching moments in Croatia's rock strewn waters. I've changed the GPS antenna (yes I know it's an 'engine') twice but with no discernable improvement. My boat is currently in Italy for regular winter maintenance and I originally asked the yard to replace the complete GPS cable in case there was a break in it which was causing the loss of GPS fix. They have reported that there is nothing wrong with the cable but the problem is caused by the proximity of the TV antenna cable which they say can interfere with the signal from the GPS antenna. Now they want to move the TV antenna and charge me quite a lot of money to do it. I'm sceptical about this. Anyone think this could be true?
 
Deleted User said:
I've owned my present boat 3 yrs and have occasionally suffered loss of GPS fix for both plotters onboard, providing me with a few bottom clenching moments in Croatia's rock strewn waters. I've changed the GPS antenna (yes I know it's an 'engine') twice but with no discernable improvement. My boat is currently in Italy for regular winter maintenance and I originally asked the yard to replace the complete GPS cable in case there was a break in it which was causing the loss of GPS fix. They have reported that there is nothing wrong with the cable but the problem is caused by the proximity of the TV antenna cable which they say can interfere with the signal from the GPS antenna. Now they want to move the TV antenna and charge me quite a lot of money to do it. I'm sceptical about this. Anyone think this could be true?
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If your TV antenna receives power up its coax to feed a receive amplifier at the antenna end, then it is possible that this could cause localised interference to a GPS signal.
The problem with GPS is it relies on receiving a very weak signal which can be prone to localised electrical interference generated by almost anything.

Usually you can eliminate this type of interference by using good quality coax cable (of the correct impedance) and not running coax cables 'bundled' together in the same conduit.

Simply increasing the distance between adjacent coax cables may solve your problem.

best of luck.
Pete
 
Mike, are they talking about the glomex-type tv aerial? If so, why not just try turning off the control box while you're underway to see if the prob is solved?

Cheers
Jimmy
 
Nah, it's bolx mike. First thing to do is as jtb says, de power the glomex in case it has an amp up there, just to eliminate that

The thing you gotta remember is that the gps signal does not travel along coax and cannot be interefered with due to 2 coax cables being close together. The engine mushroom thing receives the gps and inside the mushroom the circuitry creates a nmea0183 signal containing lat/long. This signal is just a series of +5v pulses at very low baud rate. These pulses, not the tiny GPS signals received from the satellites, go down a normal copper wire from the mushroom to your dashboard plotter. There is no way on earth a signal in the TV aerial wire will corrupt those pulses.

If the glomex is shielding the mushroom's view of the sky that's a differnet matter and could affect things

I'd suspect an intermittent break in the cable or inside the plotter's circuitry. Do any other items on the boat receive GPS position via same nmea0183 feed and do they all show no fix or does only the plotter show no fix? What about another plotter or the dsc or navtex something? Anyway, good time to fit a new n2k 10Hz mushroom and a new plotter. Go wild and fit Garmin 8000 :-)
 
We had a similar problem on our P430 a few years ago. When in the solent when heading west we had no problems at all. When coming back from the needles towards Southampton we would get to an area level with New Town creek and the signal would drop out until we reached the entrance to the Hamble. We could sit outside Newtown Creek and spin the boat and watch all the satellites drop out and then come back in. We had Raymarine kit on the boat at the time and spoke with them. They sent an engineer down with a new GPS and we took him out and it did exactly the same. Alot of head scratching followed. The engineer phoned back to the office and spoke with a colleague who then asked us if our TV aerial was on - it was - we turned it off and hey presto our GPS signal came back. Our GPS was next to the aerial (about a foot away though) and they seemed to think when this lined up with the transmitter aerials on the Isle of Wight (TV attena - GPS - Isle of Wight Transmitters) it knocked out the GPS. Turn off our TV aerial no problem at all. Apparently a couple of other boats had reported this to Raymarine at the same time as us in the same area.
 
Hi Mike

Sounds iffy. Not sure how useful this will be. We have two GPS antennae on our arch and a Glomex (see pic). The Garmin is the lower one on the left of pic mounted directly onto the arch but below the glomex, the Raymarine is higher up almost on the same horizontal plane as the Glomex. We have never had a problem with the Garmin dropping out, but the Raymarine has dropped out on on rare occasions, but has usually returned within a few minutes. From memory the Raymarine cable and the TV coax run togther down the port side of the arch, but the Garmin cable runs down the stbd side of the arch. Our Glomex amp is permenantly on.

GoLight1.JPG


Both GPS antennae are within 1m of the Glomex. Raymarine tech support might be your best port of call to substantiate or dismiss your local yards theory. It sounds more like an intermittant prob with cabling, connections or hardware.
 
Thanks for replies. Sorry my post was written a bit in haste. The boatyard referred to it as a TV antenna but actually it's a Sat TV dish as this picture shows. The arrow indicates where the GPS engine is. I suspect that the Sat TV dish is left on quite a lot whilst we are at sea as it is driven by an inverter and kids switch it on without asking me. So anyone care to speculate whether a Sat TV signal would interfere with the GPS signal? I suspect that both cables run down the port side of the radar arch. Or is it just that the Sat dome is shielding the GPS engine? I did think about raising the height of the GPS engine by fitting it on a short mast but the dome overhangs the GPS engine so it's not a simple fit

P1010908.jpg
 
Deleted User said:
Thanks for replies. Sorry my post was written a bit in haste. The boatyard referred to it as a TV antenna but actually it's a Sat TV dish as this picture shows. The arrow indicates where the GPS engine is. I suspect that the Sat TV dish is left on quite a lot whilst we are at sea as it is driven by an inverter and kids switch it on without asking me. So anyone care to speculate whether a Sat TV signal would interfere with the GPS signal? I suspect that both cables run down the port side of the radar arch. Or is it just that the Sat dome is shielding the GPS engine? I did think about raising the height of the GPS engine by fitting it on a short mast but the dome overhangs the GPS engine so it's not a simple fit

P1010908.jpg
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Looking at that, i would say re position your gps antenna as its coverage of the sky is very restricted by your sat dish.

regards pete
 
That s/s plate that the sat tv dome's mounted on cannot be helping your gps coverage ... Can't you just relocate the GPS mushroom to the other side of the arch?

Cheers
Jimmy
 
Deleted User said:
Thanks for replies. Sorry my post was written a bit in haste. The boatyard referred to it as a TV antenna but actually it's a Sat TV dish as this picture shows. The arrow indicates where the GPS engine is. I suspect that the Sat TV dish is left on quite a lot whilst we are at sea as it is driven by an inverter and kids switch it on without asking me. So anyone care to speculate whether a Sat TV signal would interfere with the GPS signal? I suspect that both cables run down the port side of the radar arch. Or is it just that the Sat dome is shielding the GPS engine? I did think about raising the height of the GPS engine by fitting it on a short mast but the dome overhangs the GPS engine so it's not a simple fit

P1010908.jpg
Click to expand...

Someone with not much knowledge about radio signals installed the GPS antenna totally incorrectly under the large satellite TV antenna or they installed the satellite TV antenna without a care about the GPS navigation antenna which they should have known it would shield?

Your best option, and probably the cheapest, is to relocate the GPS antenna to a position near the horn on the starboard side.




.
 
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lenseman said:
Someone with not much knowledge and radio signals installed the GPS antenna totally incorrectly under the large satellite TV antenna or they installed the satellite TV antenna without a care about the GPS navigation antenna which they should have known it would shield?

Your best option, and probably the cheapest, is to relocate the GPS antenna to a position near the horn on the starboard side.
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+1

Agree with that. Very poorly located. If you have been on a constant heading for a long time and then made a significant turn of say 140-180 degrees the GPS signal could temporarily drop out or degrade accuracy while it locks on to the satellites that had been in the shadow of the TV dome. But within a few minutes it should reacquire a good fix. In our experience Raymarine has not been as forgiving or as fast to acquire as Garmin antennae. Moving it to the STBD side of your radar arch should improve it especially if you can put it on a short pole (12"). I doubt it's anything to do with cable run interaction.
 
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+1 To what has been said about relocating the GPS antenna. Definitely a DIY, too... save yourself a few bob. While not necessary, I do agree with the above comment about putting it on maybe a 12" pole
 
oceanfroggie said:
Moving it to the STBD side of your radar arch should improve it especially if you can put it on a short pole (12"). I doubt it's anything to do with cable run interaction.
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Yup, it seems something got lost in the translation from the Italian boatyard. I have talked to the yard manager today and what they actually mean by interference is, as has been suggested, is that they think the Sat dome is shadowing the GPS engine too much and when they talked about moving the 'TV antenna' what they actually meant was moving the GPS engine. The emails get translated by a sweet girl in the office who's English isn't perfect (although way better than my Italian). So thats what we're going to do and hopefully that resolves the problem. Thanks for everybody's input
 
lenseman said:
Someone with not much knowledge about radio signals installed the GPS antenna totally incorrectly under the large satellite TV antenna or they installed the satellite TV antenna without a care about the GPS navigation antenna which they should have known it would shield?

Your best option, and probably the cheapest, is to relocate the GPS antenna to a position near the horn on the starboard side.




.
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The GPS antenna should be as near to sea level as possible to prevent multipath echoes.
 
jfm said:
Nah, it's bolx mike. First thing to do is as jtb says, de power the glomex in case it has an amp up there, just to eliminate that

The thing you gotta remember is that the gps signal does not travel along coax and cannot be interefered with due to 2 coax cables being close together. The engine mushroom thing receives the gps and inside the mushroom the circuitry creates a nmea0183 signal containing lat/long. This signal is just a series of +5v pulses at very low baud rate. These pulses, not the tiny GPS signals received from the satellites, go down a normal copper wire from the mushroom to your dashboard plotter. There is no way on earth a signal in the TV aerial wire will corrupt those pulses.

If the glomex is shielding the mushroom's view of the sky that's a differnet matter and could affect things

I'd suspect an intermittent break in the cable or inside the plotter's circuitry. Do any other items on the boat receive GPS position via same nmea0183 feed and do they all show no fix or does only the plotter show no fix? What about another plotter or the dsc or navtex something? Anyway, good time to fit a new n2k 10Hz mushroom and a new plotter. Go wild and fit Garmin 8000 :-)
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The electrical noise from the antenna actuators and head end amplifiers, plus the Radar pulses will all add to the noise seen in the GPS and may cause a frontend to overload.
 
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