Radio stations used in the war.

Military radio stations in the United States during World War II had to be carried by one person, like those used by windtalkers, calling for artillery and planes, but the farthest distance was only a few tens of kilometers (it was difficult to exceed 30 kilometers). In addition, a large receiver is needed. If there are two such stations, it will not exceed 10 km.

Like a spy, it is plug-in and has no battery, so although it is not as big as military, the transmission distance can reach tens of kilometers. It should be pointed out that if you send a telegraph signal, it can be far away, but if you send a voice signal, it will be very close. Military affairs must be sound signals, and spies can be telegrams. Send it slowly.

You said 3000 kilometers is impossible. Just a telegram. Four or five hundred kilometers at the farthest is not bad. In mainland cities, Kuomintang spies used machines the size of half a bed and antennas four or five meters long to send telegrams to Taiwan Province Province. Moreover, the receiver is required to have huge tuning, amplification and filtering equipment. Even now, transmitting high-power and long-wavelength radio waves requires a lot of equipment.