From the sideline:
In the DHC8-Q400 *no* handheld GPS device works on the flight deck. Ever! Handheld GPS receiver of brand X, Y and Z, iPad, iPhone ... you name it, it doesn't work. No signals received, indicating ...
1) something in the flight deck windows sufficiently attenuating the signals from the outside world
- and/or -
2) too much RF noise inside the flight deck, coincidentially blocking the GPS RX frequencies
Could be interesting to know which of the two is the major cause.