How do you increase the range?

[melyux]

I'd like this to work throughout the house. How do I increase the range past the present "a few centimeters"?

[hzeller]

There are various ways, starting with antenna matching, but this is not advisable to stay within legal limits.
I don't want to give you any advise that brings you into trouble, so I encourage you to ask a local ham operator knowing your local legislation how to do this.

[icb-]

@hzeller do you have any field strength measurements with your recommended "antenna"? My reading of 47 CFR 18.305 (FCC regulation limiting unlicensed intentional radiators outside ISM bands) limits the maximum permissible field strength to 25uV/m at 300m.

[hzeller]

I have not measured the coil, but I made the matching intentionally bad that it is good enough to reach my watch, but not much further.
Note that you'll get mostly inductive coupling with this kind of 'antenna'.

[melyux]

Just enough for a room, perhaps? A few centimeters makes this useless for most things (DCF77 wall clocks, in my case). And 77.5khz doesn’t interfere with anything here in the US anuwau.

[hzeller]

Should be doable. Ask your local ham op how.