Henry Kiefer wrote:
Efficient antennas at that frequency are effectively very long
bits of wire. The ferrite rod is small compared to the wavelength
and very inefficient at generating a far field.

This is the antenna of the DCF77 transmitter (same frequency):
http://de.wikipedia.org/wiki/Bildcf77.jpg

OK Iwo. But why a small receiving ferrite antenna works here? A
non-saturated (=linear, and that means the superposition theorem works)
antenna system is reciprocal as antenna theory predicts. So you should
explain where the difference is!

At LF, rarely is the problem "not enough amplitude of received signal",
so past a certain point there isn't much need to make the receiver
antenna more efficient. The problem is always "too much noise!". So
antenna designs are usually built around nulling out local noise, and
loop antennas will get rid of the mostly electric-field local noise.
And they have some directionality (notably sharp nulls) which can help
get rid of specific further-away noise.

Tim.