Swanfis
Thanks for taking the trouble to reply. I am sure I have had this problem in other aircraft as well. I expect it's related to a radio shadow caused by Snowdon, unless your transmitters are on top of the mountain. What's peculiar is how the 125.47 signal propagates so well, right through Snowdonia at low level and down to Welshpool.
My radios are KX-170, original fit in the Warrior and ancient in technical terms although still quite common. I doubt if the radiation pattern has much to do with it because the antennas are regular whip affairs.
I expect the phenomenon is completely repeatable, but like most aircraft problems probably wouldn't happen if I went out there specifically to demonstrate it to you!
Maybe someone based at Caernarvon could comment?
David