Radio eats GPS signals
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Radio eats GPS signals
Hi folks,
This is 'out of left field' as regards aviation, but I know that some of us share a recreational love of sailing. Have any private fliers experienced any similar problems - airborne or otherwise?
Bought a new NASA Marine DSC VHF radio. Have a Magellan Meridian GPS. Both work fine - on their own. Switch on the radio, whether interfaced or not and the GPS loses all signals. Just being close (c. 1 - 1.5m) and on independant power supplies is enough for the beast to lose the plot.
Any tech person out there got any ideas as to a solution?
Thanks in advance.
This is 'out of left field' as regards aviation, but I know that some of us share a recreational love of sailing. Have any private fliers experienced any similar problems - airborne or otherwise?
Bought a new NASA Marine DSC VHF radio. Have a Magellan Meridian GPS. Both work fine - on their own. Switch on the radio, whether interfaced or not and the GPS loses all signals. Just being close (c. 1 - 1.5m) and on independant power supplies is enough for the beast to lose the plot.
Any tech person out there got any ideas as to a solution?
Thanks in advance.
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Most GPS sets have an active antenna, that is an antenna with a transistor amplifier built in. It is very easy to swamp this amplifier with signals from other equipment and like all transistiors that are overloaded, they switch off, preventing the signal reaching the receiver. Simple solution, move them further apart.
Other problems could be caused by high frequency power supplies, in which case some sort of line filter may cure the problem. A ferrite clamp like they use on computer leads is one option.
Other problems could be caused by high frequency power supplies, in which case some sort of line filter may cure the problem. A ferrite clamp like they use on computer leads is one option.
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All modern radio receivers have an inbuilt oscillator, which generates a signal to create an intermediate frequency. At very close range this oscillator acts like a very low powered transmitter. The weak signal does not require the same standard as an ordinary transmitter, and it probably has a lot of harmonics, and other unwanted characteristics. The unintended transmission by your radio, and reception of these oscillator signal signals by your GPS is likely to be the problem.
Incidentally, the reason why your radio is not adversely affecteed by its own oscillator is due to design and careful selection of the oscillator and IF.
Check this out. Tune an SSB signal on an AM shortwave radio. random tune another radio positioned in very close proximity. The oscillator harmonics of the second radio can beat with the SSB signal to enable you to understand the signal.
Incidentally, the reason why your radio is not adversely affecteed by its own oscillator is due to design and careful selection of the oscillator and IF.
Check this out. Tune an SSB signal on an AM shortwave radio. random tune another radio positioned in very close proximity. The oscillator harmonics of the second radio can beat with the SSB signal to enable you to understand the signal.
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Noggin and autoflight,
Many thanks for replying. I fear that since the Magellan Meridian does not have an external aerial socket, I will have to try and get it and the radio as far apart as possible. Since I like to have access to both at arms length, this is going to be a major problem.
Isn't progress wonderful!
jetfour
Many thanks for replying. I fear that since the Magellan Meridian does not have an external aerial socket, I will have to try and get it and the radio as far apart as possible. Since I like to have access to both at arms length, this is going to be a major problem.
Isn't progress wonderful!
jetfour
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Hi,
As autoflight states there are harmonics being emitted from the radio and this is what is concerning me. It seems that the radio is not containing them as well as it could do so I have a few questions.
1) Is the case of the radio plastic or metal ?
2) Does this problem go away if you use just batteries in the GPS i.e. disconnect the power lead and just use the GPS with batteries only.
3) Is the radio "type approved", is there a sticker/label at the back or bottom saying it's in accordance with *** rules ? Some radios do not have this and that means they have either failed radiation tests or other tests. This could be one reason for the problem.
I would be glad to hear of your findings also follow what Noggin says about the ferrite clamps on the power lead of the radio, try a clamp right up by the radio as near as you can and one by the power supply unit/transformer.
Good luck, let me know,
LL
As autoflight states there are harmonics being emitted from the radio and this is what is concerning me. It seems that the radio is not containing them as well as it could do so I have a few questions.
1) Is the case of the radio plastic or metal ?
2) Does this problem go away if you use just batteries in the GPS i.e. disconnect the power lead and just use the GPS with batteries only.
3) Is the radio "type approved", is there a sticker/label at the back or bottom saying it's in accordance with *** rules ? Some radios do not have this and that means they have either failed radiation tests or other tests. This could be one reason for the problem.
I would be glad to hear of your findings also follow what Noggin says about the ferrite clamps on the power lead of the radio, try a clamp right up by the radio as near as you can and one by the power supply unit/transformer.
Good luck, let me know,
LL
Last edited by Liquid Lunch; 12th May 2002 at 22:12.
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Radio eats GPS signals
Liquid Lunch,
Again thanks for replying.
In answer to your questions:
1. The radio has a metal case.
2. No, the problem is no different whether 'on the bus' or battery power.
3. Yes, the set is type approved and a latest model. NASA Marine SX35 DSC. (Full Class D spec.)
Mighty Moderator, many thanks for your help.
jetfour
Again thanks for replying.
In answer to your questions:
1. The radio has a metal case.
2. No, the problem is no different whether 'on the bus' or battery power.
3. Yes, the set is type approved and a latest model. NASA Marine SX35 DSC. (Full Class D spec.)
Mighty Moderator, many thanks for your help.
jetfour
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> No, the problem is no different whether 'on the bus' or battery power.
This would seem to rule out noise coming in via the power lead (assuming it was disconected at the GPS end of the lead when tested on battery).
If you are having problems when the radio is in rx mode you will probably have serious problems when it's transmitting as the power levels are very much higher - but perhaps that doesn't matter as you transmit less frequently.
I've seen equipment with type approval labels that clearly don't
meet all the standards they are claiming.
This would seem to rule out noise coming in via the power lead (assuming it was disconected at the GPS end of the lead when tested on battery).
If you are having problems when the radio is in rx mode you will probably have serious problems when it's transmitting as the power levels are very much higher - but perhaps that doesn't matter as you transmit less frequently.
I've seen equipment with type approval labels that clearly don't
meet all the standards they are claiming.
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Cw
Thanks for your input.
The nub of the problem for me lies in the fact that for these new, expensive and now compulsory DSC radio transceivers to provide their intended functionality, the GPS must be on and interfaced at all times. This is so that if the operator has need to hit the distress button, the radio sends an automatic broadcast including GPS position. If the radio is wiping out the GPS signals, even on receive (which it is) I am left with Type Approved equipment costing many hundreds of pounds which don't do the business.
Thanks for your input.
The nub of the problem for me lies in the fact that for these new, expensive and now compulsory DSC radio transceivers to provide their intended functionality, the GPS must be on and interfaced at all times. This is so that if the operator has need to hit the distress button, the radio sends an automatic broadcast including GPS position. If the radio is wiping out the GPS signals, even on receive (which it is) I am left with Type Approved equipment costing many hundreds of pounds which don't do the business.
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Jetfour,
As painful as it might be, I think to get around this problem you will need to buy a GPS external antenna. I've seen them for around 40 pounds STG. This solution (not cheep I know) means that the antenna, which is picking up the rubbish from the radio, will now have the chance of being outside and away from the offending radio, plus it will increase the signal strength of the GPS transmissions as the antenna has a built in amplifier, hopefully tuned to the GPS freq. and not broadband as that would spell trouble all over again.
Another option I might consider if possible and that is to exchange the GPS/radio for a different one, a different manufacturer perhaps, if that is an option for you of course.
Good luck !
LL
As painful as it might be, I think to get around this problem you will need to buy a GPS external antenna. I've seen them for around 40 pounds STG. This solution (not cheep I know) means that the antenna, which is picking up the rubbish from the radio, will now have the chance of being outside and away from the offending radio, plus it will increase the signal strength of the GPS transmissions as the antenna has a built in amplifier, hopefully tuned to the GPS freq. and not broadband as that would spell trouble all over again.
Another option I might consider if possible and that is to exchange the GPS/radio for a different one, a different manufacturer perhaps, if that is an option for you of course.
Good luck !
LL
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LL
Yes, an external aerial sited well away from the offending radio would be the obvious solution. Trust me to buy a GPS set that doesn't have an external aerial socket!
Am going to put a bit of pressure on the radio manufacturer as several people have suggested that this set may very well not be inside the EC's electro-magnetic emissions standards which are now mandatory and which would threaten their CE mark on the product.
A bit of 'naming and shaming' might well follow!
Anyway, if I ever get to a solution I will post here (if anyone is interested) and once again many thanks to all the ppruners who have taken the time to make suggestions.
jetfour
Yes, an external aerial sited well away from the offending radio would be the obvious solution. Trust me to buy a GPS set that doesn't have an external aerial socket!
Am going to put a bit of pressure on the radio manufacturer as several people have suggested that this set may very well not be inside the EC's electro-magnetic emissions standards which are now mandatory and which would threaten their CE mark on the product.
A bit of 'naming and shaming' might well follow!
Anyway, if I ever get to a solution I will post here (if anyone is interested) and once again many thanks to all the ppruners who have taken the time to make suggestions.
jetfour
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Jedi Knight,
Yes indeed, a lot of GPS sets have a BNC socket under their flip up aerials. My friend's Garmin48 is like this. The Magellan Meridian is totally self contained with NMEA and power conections only. No flip up - no external aerial connection.
Anyway, just returned from a weekend's golf in Donegal. My letter to NASA Marine has now been finely honed in the bunkers of nether Ulster! Black Bush is a marvellous mental stimulant. (and before you start folks, Black Bush is a very superior brand of whiskey!)
Watch this space,
jetfour
Yes indeed, a lot of GPS sets have a BNC socket under their flip up aerials. My friend's Garmin48 is like this. The Magellan Meridian is totally self contained with NMEA and power conections only. No flip up - no external aerial connection.
Anyway, just returned from a weekend's golf in Donegal. My letter to NASA Marine has now been finely honed in the bunkers of nether Ulster! Black Bush is a marvellous mental stimulant. (and before you start folks, Black Bush is a very superior brand of whiskey!)
Watch this space,
jetfour
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> which would threaten their CE mark on the product.
Unfortunately the CE marking scheme is not as good as (for example) the FCC scheme, mainly because it's possible for manufacturers to self-certify their own equipment.
A responsible manufacturer will submit samples of their product for testing by a third party test house, who will issue a report to the effect that xyz meets standards a,b&c etc
Irresponsible manufacturers will just buy the little stickers.
Once while testing a computer for compliance we found that some of the test equipment we were using was itself radiating in excess of the applicable standard!
The CE mark is meant to mean that the product meets all applicable EEC standards. For electronic equipment I believe this now also includes a standard for susceptibility to interference from other sources. Perhaps the problem is the GPS Rx not the Radio.
You could try asking both companies for copies of their test reports but don't hold your breath. Even if they have them I suspect most companies will just ignore such requests unless you want to buy 1000's of sets.
Unfortunately the CE marking scheme is not as good as (for example) the FCC scheme, mainly because it's possible for manufacturers to self-certify their own equipment.
A responsible manufacturer will submit samples of their product for testing by a third party test house, who will issue a report to the effect that xyz meets standards a,b&c etc
Irresponsible manufacturers will just buy the little stickers.
Once while testing a computer for compliance we found that some of the test equipment we were using was itself radiating in excess of the applicable standard!
The CE mark is meant to mean that the product meets all applicable EEC standards. For electronic equipment I believe this now also includes a standard for susceptibility to interference from other sources. Perhaps the problem is the GPS Rx not the Radio.
You could try asking both companies for copies of their test reports but don't hold your breath. Even if they have them I suspect most companies will just ignore such requests unless you want to buy 1000's of sets.
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You might try an experiment - try wrapping the GPS Rx in cooking foil leaving just the antenna area clear (and perhaps part of the diaplay and controls needed to check it's working). If this extra shielding works then it demonstrates that the interferrence isn't getting into the GPS via the antenna.
If this does work you may be able to take the GPS Rx apart and spray the inside of the case with conducting paint (available from electronic distributors like RS Components). However this stuff is messy and it's prone to flaking on some plastics if it gets humid- with dire consequences if it then floats about inside the electronics).
Probably best to try and get another GPS system on sale or return.
If this does work you may be able to take the GPS Rx apart and spray the inside of the case with conducting paint (available from electronic distributors like RS Components). However this stuff is messy and it's prone to flaking on some plastics if it gets humid- with dire consequences if it then floats about inside the electronics).
Probably best to try and get another GPS system on sale or return.
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Jetfour
Note you say the radio has a metal case. Can/have you earthed this case. This can help - but tend to agree the "best" answer is to move the GPS aerial to a remote location away from the radio, maybe a quarter of the way up the mast (assuming sail boat). Don't put it at the top - your DSC radio aerail will be there!
Note you say the radio has a metal case. Can/have you earthed this case. This can help - but tend to agree the "best" answer is to move the GPS aerial to a remote location away from the radio, maybe a quarter of the way up the mast (assuming sail boat). Don't put it at the top - your DSC radio aerail will be there!
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Jetfour,
As you don't have a socket for an external antenna, you might like to consider a GPS re-radiator. This device receives the GPS signals, amplifies them and then reradiates them through a little antenna that you can locate close to the GPS device. The GPS then receives the signal through it's internal antenna as normal.
Due to my car windshield being GPS proof
I bought the RRAD-45 at the following link and it works brilliantly.
GPS Warehouse: Smart Antennas
Hope this helps...
m.
As you don't have a socket for an external antenna, you might like to consider a GPS re-radiator. This device receives the GPS signals, amplifies them and then reradiates them through a little antenna that you can locate close to the GPS device. The GPS then receives the signal through it's internal antenna as normal.
Due to my car windshield being GPS proof
I bought the RRAD-45 at the following link and it works brilliantly.GPS Warehouse: Smart Antennas
Hope this helps...
m.
