The right frequency + the receivers being in the right places i guess. Like mobile phones really.Well I know devices can be made that small.. but how would it transmit a usable signal, is what I want to know?
Antennas are most efficient near a quarter of the wavelength of the transmitted signal. This is why CB radio antennas (frequency ~27MHz or 11 m wavelength) are much longer than wireless network antennas (frequency ~2.4 GHz, or 12.5 cm wavelength). Longer frequency <--> further transmission is mostly applicable to the near-field, since a source with a lower frequency will have a larger near-field region (the near-field being 1-2 wavelengths away from the antenna). I believe for transmission outside the near-field you need an approximately quarter wavelength antenna -- this is one of the reasons you don't see very many ultra-low frequency radio transmissions: the size of the antenna required. The other is of course the low bandwidth available.Usually you have a limit range due to power/transmitter of the unit (being small doesn't have that powerful stuff) but you "could" transmit in lower frequency/cycle which has a longer distant. All you need is a pulse really so you don't need it to be high frequency. Then all you need is a receiver to pick up that particular signal and follow it.
Antennas are most efficient near a quarter of the wavelength of the transmitted signal. This is why CB radio antennas (frequency ~27MHz or 11 m wavelength) are much longer than wireless network antennas (frequency ~2.4 GHz, or 12.5 cm wavelength). Longer frequency <--> further transmission is mostly applicable to the near-field, since a source with a lower frequency will have a larger near-field region (the near-field being 1-2 wavelengths away from the antenna). I believe for transmission outside the near-field you need an approximately quarter wavelength antenna -- this is one of the reasons you don't see very many ultra-low frequency radio transmissions: the size of the antenna required. The other is of course the low bandwidth available.[/QUOTE]Usually you have a limit range due to power/transmitter of the unit (being small doesn't have that powerful stuff) but you "could" transmit in lower frequency/cycle which has a longer distant. All you need is a pulse really so you don't need it to be high frequency. Then all you need is a receiver to pick up that particular signal and follow it.