GPS signal reduction
 

Bought a brand new GPS which works perfectly outside my &*&....in the flight deck no signal at all. I have had one theory presented which says that there is a lead content in the windows which blocks the signal. Sounds unlikely...any thoughts?

The flight deck windows are coated with a metalised film to combat UV light at altitude. The windows may also incorporate a thin film or wire grid heating system to combat icing. The windows will also be electrically bonded to the airframe. From a radio wave point of view, the windows might as well be a solid metal sheet.

You are attempting to receive very weak GPS signals from what amounts to the inside of a Faraday cage. Hence your device cannot work without connecting it to an external antenna mounted outside the shielded area or on the outer skin of the aircraft.

Try to put the GPS receiver behind the sidewindow, works on the 320 pretty well. No idea about other types.

Some single channel gps will not work unless they acquire signal lock at lower speeds, i.e. Before takeoff. The algorithms in more basic gps cannot cope at cruise speed.

My iPad GPS works fine in its mount on the No.2 window frame of a B737NG.

Reception depends entirely on the kind of windows fitted. In the 737 the No. 3 windows can either be glass (thus heated through a vapor deposited metal layer somewhere in the middle) or plastic, which will help your GPS reception tremendously. If all windows are electrically heated (like on the 777 for instance or more expensive 737s) you need a heck of a sensitive receiver (some of the bluetooth GPS receivers available work well).

I find my iPad clipped by the No. 2 window on the 777 works okay – it does drop out intermittently though, and can take a very long time to acquire a signal to start with. Bluetooth receivers seem to work excellently either sat behind the window handle or suction-cupped onto the No. 3 window.