Another GPS Q?

[cglanton]

Hi all. Recently fitted a Raymarine RC400 to outside of bulkhead and all worked fine hooked it up to NASA DSC VHF which is on inside of said bulkhead - All worked position shown on VHF.

Went sailing with it for the 1st time last week and everytime the VHF was turned on the GPS lost all satelite signals.

I've never heard of VHF causing GPS interference before - any ideas??

Cheers

Chris

 

[jackho]

I have a similar problem - Silva 10 radio connected to Garmin GPS. When both are powered up position reads on radio when connection applied and no problem with GPS. Power down and the GPS will not switch on with connection made.
Have tried several remedies without success so interested in any suggestions.

 

[Channel Ribs]

Sounds like the the vhf(s) may be supplying voltage via the nmea wires.

Perhaps try to disconnect all but the power to each see if that makes a difference, if it does then re-check the wiring diagram and connect each in turn?

 

[Cruiser2B]

There are different NMEA sequences - maybe they're not compatible. This might help: http://www.gpsinformation.org/dale/nmea.htm

Good luck.

 

[grumpy_o_g]

If you're actually losing the satellite lock it sounds like your VHF set is leaking (radiating in the RF frequency when it shouldn't be) - it's unusual for a set to do this at any strength when in receive mode though. Is there a good strong signal from at least some of the satellites in view?

I assume the GPS isn't anywhere to near the antennae though it should affect the GPS you're quite right.

Can you leave everything hooked up but move the GPS away from the VHF unit and see if it behaves the same? Another trick to try is something metallic (even aluminium foil will do it) wrapped around the VHF unit and then earthed. If this improves the situation then you have a good idea of the culprit.

 

[brianrunyard]

Is the GPS ok if you disconnect it from the VHF? If it is check the connections.
Your GPS is NMEA 0183, whats the VHF?

 

[cglanton]

Thanks all will fiddle at the weekend and let you know how i get on. interesting that a few think wrong connections, especially given the her in doors was reading out the colours in the manual!!!!!!!! Sexist I might be, but funny feeling I'm going to be proved right!!

 

[Oldhand]

Ask NASA what EMI (electromagnetic intereference) specification their VHF conforms to. If they can supply a spec., look it up and I wouldn't be surprised to find your RC400 GPS antenna is being swamped by RF from the VHF when it transmits.

After all, an ICS Nav6 Navtex display unit that has no transmit capability and conforms to a standard pleasure boat use EMI spec, wipes out GPS if the antenna is within a few inches and opens the squelch on an Icom handheld VHF at half a meter or more.

 

[cglanton]

I had a fiddle today and even with the NMEA disconnected it still happened so not poor wiring! Called Raymarine and they think its some form of 'noise' leaking from the VHF - looks like I'm buying a new VHF - bugger.