I have a DCF77 radio clock module. I want to improve the reception from
Frankfurt (im in the UK). It has a small ferrite rod, which I can get a
signal on (77.5khz), but it tends to drop out during the day. I don't
know much about antenna design at these frequencys sort of hanging wires
across the garden.

I have a larger, thicker ferrite rod laying about. It's over twice the
length. Is this likely to work much better? How do I use it? Can I
just wind the same number of turns around the rod, as on the smaller
one, or is it more complicated than that?

Stuart.