hi @all
my question is: the antennas for dcf77 signal on the market are very big. But it must be possible to get this smaller because on Aldi you can buy this watch: Aldi Süd: Sempre Funkwecker für 9,99€ im Angebot
and this watch is very small and must have a DCF77 antenna inside.
So did someone know how this is possible?
thx
hape
The dcf77 signal transmits on a very low frequency of 77.5 KHz. This is too low to use a "proper" quarter / half wave dipole.
To get it small you use a coil of wire and a ferrite core, like in the old medium wave transistor radios.
My Casio watch receives the DCF-77 at full strength, and I'm at 400 km distance from the transmitter.
The antennas that can be bought are not very good. I read that only the larger ones receive it well.
Here is a project with DCF-77 : DCF77 Project | Blinkenlight
and a test with modules : DCF77 Receiver Modules | Blinkenlight
I must be possible that a manufacturer makes a good and small DCF-77 receiver with the antenna included, but I can't find it.
A small antenna is always going to be poorer in performance than a full-size 1/4wave or dipole,
its simple physics. If its not even resonant too, then it'll be awful.
However for receiving broadcast signals (here transmitted at high power form a big aerial),
this is usually irrelevant as even a woefully inadequate receive aerial is fine.
Point-to-point comms where the transmit power is limited means having to get good antenna
performance
hi @all
so it must be possible because (as i said in my first post) in the watch from Aldi there must be a small antenna inside. So i will do research to get information how this watch did do this.
hape
I have seen a picture of it, but I can't find it.
The core has ends with an angle to make it fit inside a round watch. And there are copper wire windings around it. It is the same as the larger ferrite antennas, but much smaller.
In other words, the antenna is the full size of the watch (which has a plastic case. 
)
hi
yes it sounds as if it is the whole watch but this also smaller than the antennas you can bought for DCF77. Also the height is only a tenth or less of the antennas you can buy.
hape
Peter_n:
My Casio watch receives the DCF-77 at full strength, and I'm at 400 km distance from the transmitter.
For longwave, that's "right next door".