On the above loop, I heard Paris Orly NDB "ORW" on 402.0khz this morning, my first signal from the French capital.
I have also ordered Edward Noll's book "25 Simple MW and Tropical Band Antennas" as I loved that series of Mr Nol's books as a youngster. So I might try my hand at a tropical band antenna next.
I also quite fancy having a bash at a larger LF loop. My experiments with HF loops have shown me that the size is not at all critical, and I have come down from 1m diamater to barely 40cm diameter with no noticeable loss of received signal. But my instinct tells me a larger LF loop might make all the difference in pulling in these very weak NDB signals from around NW Europe.