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***Tom - Raymarine - Moderator***

Hello Magic8,

I hope Chuck doesn't mind me chipping in here, but some local knowledge might help clear things up. I'm based in Sydney, and one of our dealers has brought this to my attention.

The RS150 is a hugely accurate and reliable GPS antenna - I place considerable trust and confidence in their accuracy and reliability. The ST1-STNG convertor doesn't have any influence on the GPS position, it just blindly passes through what it receives and if there were a fault with that then the result would be no data rather than incorrect data.

This said, there are two things that we know of and have seen many times that can cause temporary but significant position errors in a perfectly-working RS150 (or similar) that has a good view of the sky:

1. RF interference. We have often seen noisy electrics or electronics radiating sufficient noise to partly or completely drown out the very weak GPS signals. Common culprits are LED light drivers, TV antennas, USB devices and 5V charging outlets, invertors and charge controllers, but almost anything electrical that's more complex than an incandescent globe is a potential culprit.

2. In Australia, Differential GPS mode. Modern antennas are sensitive enough to pick up the fringes of the Differential (SBAS) services available in other parts of the world. On the East coast we get Japanese MSAS, in NZ they get American WAAS, and in WA they pick up Indian GAGAN. This sounds good, but in fact what can happen is that the system uses only satellites for which there are differential corrections available, which means in fact a much less accurate fix (larger position error - there is always some position error in GPS/GNSS.) We therefore advise everyone in AU/NZ to turn off Differential mode in satellite setup.

Please disable Differential mode first. If no improvement, the problem is probably RF interference that a Raymarine Service Dealer could help diagnose, but if in doubt you can give us a call on the contact details at http://www.raymarine.com.au/view/index-id=1154.html

Regards,
Tom