Wireless transmitting und reception devices work on specific frequencies. The higher the quality of the receiving or transmitting device, the better is the correlation between the dial markings and the real operation frequency. Very high accuracy of the frequency of a receiver or transmitter can be reached, when crystals are used. Because these crystals used in receivers or transmitters are expensive, engineers developed ways to safe the cost of many different crystals and ensure a high frequency stability anyway.
Frequencies are measured in Hz (cycles / second), or in multiples, for example kHz (Kilohertz = 1000 Hz), MHz (Megahertz = 1000'000 Hz) and GHz (Gigahertz = 1000 MHz).
In the very early time of wireless telegraphy, frequencies have been indicated inthe form of a wavelength in meters angegeben, you can use the formula 300'000/ Wavelength in meters to calculate the frequency in kHz from a given wavelength.
In older British sets, you might encounter the dial marked in cps (cycles per second) instead of Hertz.
The frequency spectrum has been divided in different bands which were allocated for certain use:
- VLF (Very Low Frequency): 3 - 30 kHz; used for the communication with submarines while under water, not in use by the Swiss Army.
- Longwaves: 30 - 300 kHz; used for time signal stations, direction finding (non directional beacons) and from 150 - 300 kHz for broadcasting stations in the longwave band (in Europe, but not in Switzerland)
- Mediumwaves: 300 kHz to 3 MHz; used from 500 - 1600 kHz for mediumwaves broadcasting stations, for amateur radio (160 m - band) and from 15600 - 3000 kHz for military and maritime communication.
- Shortwaves: 3 - 30 MHz; shortwave broadcasting and amateur radio in narrow segments allocated to this use („broadcasting bands“ and „ham bands“), and for military communication in the complete shortwave band.
- VHF / FM - Band: 30 - 300 MHz; mainly used for military communications in the 30 - 88 MHz range, for FM broadcasting in the 87,5 - 108 MHz range, for aeronautical communications in the „Air Band“ 108 - 132 MHz (here, AM is used on contrast to the rest of communications in the VHF band), for aamteur radio (2m - band), for public services and for television (old VHF channels 5 - 12, today in Europe used for DAB / DAB+).
- UHF: 300 MHz - 3 GHz; used for military aeronautical communication in the 225 - 400 MHz range, for amateur radio (70 cm band) and television (old UHF channels 22 - 70), mobile telephony and WLAN, bluetooth.
- SHF: 3 - 30 GHz; used for military and civilian microwave communications, radar, but also mobile telephony and WLAN
In historic german sets, frequencies above 30 MHz have been addressed as „Ultrakurzwellen“, that's why the „UKW Empfänger“ of the german Wehrmacht are operating on frequencies around 30 MHz.