antenna spacing on a sternrail

[JumbleDuck]

As someone who's measured the performance of a few antennas, GRP can have significant influence...

Thanks - that's really interesting.

 

[[70521]]

As someone who's measured the performance of a few antennas, GRP can have significant influence.
GRP with lots of rain or heavy spray running over it even more so.

It begs the question how accurate do you need a GPS fix to be?

 

[RAI]

Already mentioned but here is a link to a copy.
http://www.ussailing.org/wp-content...ore/SAS Studies/2007 Radar Reflector Test.pdf
for those interested in the effectiveness of passive and active radar reflectors.

 

[crashtack]

Seconded. This thread has been highly informative. It's not often that such a wealth of knowledge is spread around, but this has been fascinating.

As well as saving on paying someone to have a look and then tell me......

 

[prv]

Modern GPS units are fantastic at getting an adequate fix in poor conditions, but give the units a clear view of the sky and they do better.

The advantages of the clear sky view are noticeable in situations such as when trying to determine if the anchor has moved slightly and reducing the incidence of false anchor alarms. The other improvement is the accuracy of COG data which helps tide estimation etc. The chance of getting an SBAS fix in marginal areas is much better. The benefits are greater in adverse conditions such as when a wet deck and sails create some additional attenuation and multipath distortion.

These are all good points. I guess many of us are happy as long as we have some kind of fix, without considering the quality of it. It's something I might think about more in future now.

My main navigation GPS antennas are on deck - or at least, the old Seatalk one is flush-mounted on the coachroof just ahead of the windscreen, whereas the new plotter has an inbuilt antenna that will need to see out of the pod it's mounted in. But that's just one thin skin of GRP which I'm sure makes no real difference. The antennas below decks are for the VHF and AIS (display, not transmitter), and for the Garmin 128 that drives the Yeoman plotter. The latter of those did need to be mounted in a window to get acceptable performance out of the mid-90s receiver in wet conditions, which supports your point.

Pete