GPS losing fix at Toronto Island

[sailingmonica]

Here goes the question that puzzled marine dealers and sailors alike. If there is an explanation I know you guys will find it.

I have a Standard Horizon CP175C GPS Chartplotter on my boat. It had never failed me, not in Canada, not in the USA. Last August we went to the Toronto Island, entered through the Eastern Gap and headed for the Toronto Island Marina. As we were just entering the buoyed channel leading to the marina the GPS lost the fix.

Of course, I thought the unit just died and I replaced it immediatelly with the spare one - same make and model. The new one wasn't able to get a fix either, so at that point I thought it was the (external) antenna that was faulty.

A few days later we left the island and again headed for the Eastern Gap. As we were just making our way into the main shipping channel between the island and the main land the GPS came back.

Now, there are six antennas in a cluster located on the island just South of the Toronto Island Marina. I thought they were causing the interference that eventually caused the GPS to lose the fix until I spoke with other sailors and none of them had any problems in the area. They also had other brands of GPS - Garmin, Lowrance etc.

Why would the antennas only affect my Standard Horizon? Does it even make sense?

What other brand that also uses C-Map works on the island?

How come my Standard Horizon had no problem working around Camp Lejeune military base for example, but fumbled here?