Hope these comments help.
I had noticed that I was frequently losing the GSM signal. I assumed that this was just the way it was going to be as I usually fly about 3000 - 3500 feet and the mobile masts are obviously transmitting most of their energy horizontally rather than vertically. I managed to maintain a connection (on iPhone 13) for about 30 - 40 % of the time.
I fly a Jabiru J430 and had been resting the phone on the P2 seat. The P2 seat has the header tank immediately beneath it with 5 litres of Avgas in it. I have no idea of the signal attenuation of Avgas, but I moved the phone to a position in the P1 footwell. In this location the signal is only attenuated by the thickness of the glass fibre fuselage. The result was surprising and encouraging.
I found that on my usual route I was holding the GSM signal almost 100% of the time. almost no drop off, signal was in the green.
Lesson learned is that the GSM signals are already weak for reasons that others have discussed so the position of the phone can be critical for maintaining and getting a good data stream for the IGRID function. I appreciate that this is an aircraft specific comment, but I would suggest that if you are getting GSM drop-off try a different position for your phone to improve reception
Peter
