As an alternative you can actually use magnetic induction to transmit data at low frequency. That will work up to a few meters.
They can easily be made to go 50m, 100m or more if needs be, but you might get in trouble if you interfere with an inductive loop used by a hard of hearing person.
Magnetic induction transmitters were once a popular hobby project. I did often run a loop of wire around a room linked to a high power audio amplifier when I was a kid. Strangely enough there is zero information on the internet about them now.
There is quite a bit of info out there, although not as much in the hobby department.
They're not very well suited to data transmission either, since just about "anything" will be interference.
If you really want to transmit EM waves at low frequency (at low power 1 W< and low efficiency 1%<) you can use a ferrite rod antenna.
They tend to be very directive (too directive for something moving).