I can't really help you with ferrite antennas for transmitting, but can
tell you that if you google around for "lowfer" and the Longwave Club
of America http://www.lwca.org/ you will find a lot about antenna
designs that are suitable for this band. They will also might have
recommendations for frequencies of operation that are legal for
transmission in your home country (I don't even know what that is!)

Thanks. I will look there.

I'm a little surprised that your achieved range was so small from a
ferrite rod antenna, actually. Did you really tune both antennas, in
place and in circuit, for resonance? The resonance is so so super
narrow that strays between design and circuit make a big difference. I
mean, CRT screens with flybacks, and faulty flourescent lamp ballasts,
and incadescent dimmers radiate all sorts of crap around the LF
spectrum for blocks, and they aren't even trying to be intentional
transmitters! And don't get me started about induction heaters and
welding machines, those can be heard across several states!

Maybe the time-code receiving IC is a bad design. I don't know. It's
operating current is 500uA only. That is very small. It can receive the
time-code over 2000km with such an antenna with an transmitter EIRP of 30KW.
The receiving antenna is 700Hz bandwidth. I don't think this is super
narrow. Even if we look at the time-code receiver quartz filter with a
bandwidth of about 10Hz I can met it with my stable wave generator. It is a
PLL-design with a clock quartz. Should be typical 10ppm. I don't have a very
good frequency meter to verify it.

In my second transmitter experiment I used a not-resonated driver design. So
there are no problems with detuning the transmit antenna expected. It is
just driven by the 77.5KHz power signal.

CRT screen is off if I experiment. Otherwise I seen a very big CRT signal at
the receiver...

If the two ferrite rods will detune because of the close proximity I cannot
control it. I don't think so.

If you can hear induction heaters or something this is surely with a very
big antenna and a resonable good receiver design.

- Henry