Radio Technology Fundamentals
Waves, frequency, wavelength, modulation types and frequency bands in Germany — the foundation for SDR and amateur radio.
1.1 How radio works
Radio is the wireless transmission of information via electromagnetic waves. A transmitter generates a high-frequency carrier signal and modulates it with the payload information. A receiver filters out exactly that frequency and demodulates the signal.
| Quantity | Formula | Example |
|---|---|---|
| Wavelength (λ) | λ = c / f (c = 300,000 km/s) | 433 MHz → λ = 69 cm |
| Frequency (f) | f = c / λ | 2 m band: f = 144–146 MHz |
| Bandwidth | Channel width in Hz | FM broadcast: 200 kHz · TETRA: 25 kHz |
| Free-space loss | increases with frequency and distance | 2.4 GHz attenuates more than 70 cm |
| Range | depends on frequency, power, antenna | Lower frequencies = greater range |
Rule of thumb for antenna length: Quarter wavelength = c / (4 × f). For 400 MHz (TETRA): 300,000 km/s / (4 × 400,000 kHz) = 18.75 cm per rod. A simple dipole for TETRA: 2 × 18.75 cm.
1.2 Modulation types
| Modulation type | Abbr. | Principle | Use |
|---|---|---|---|
| Amplitude modulation | AM | Carrier amplitude varies | Medium wave, VHF aviation |
| Frequency modulation | FM | Carrier frequency varies | FM broadcast, analogue emergency-services radio (old) |
| Single sideband | SSB | Only one sideband, no carrier | Short wave, maritime communication |
| Phase-shift keying | PSK | The phase is switched | Satellites, digital HF modes, FT8 |
| Frequency-shift keying | FSK | The frequency jumps between values | Data radio, POCSAG, TETRA basis |
| Digital time multiplex | TDMA | Several users share one channel in time | TETRA, GSM, DMR |
| π/4-DQPSK | Phase modulation, robust against interference | TETRA |
1.3 Frequency bands in Germany
| Band | Frequency | Wavelength | Typical use |
|---|---|---|---|
| LF/MF | 30 kHz – 3 MHz | 10 km – 100 m | Maritime radio, DCF77 (77.5 kHz time signal) |
| HF (short wave) | 3 – 30 MHz | 10 – 100 m | Amateur radio, broadcast, maritime radio |
| VHF | 30 – 300 MHz | 1 m – 10 m | FM radio, analogue emergency services (old), aviation, 2 m band |
| UHF | 300 MHz – 3 GHz | 10 cm – 1 m | TETRA emergency services, PMR, 70 cm band, GSM, LTE |
| SHF | 3 – 30 GHz | 1 – 10 cm | Wi-Fi, satellite TV, radar, 3.4 GHz amateur radio |
Amateur radio bands
| Band | Frequency | Range | Typical use |
|---|---|---|---|
| 160 m | 1.81 – 2.0 MHz | Medium wave | Night DX, local traffic |
| 80 m | 3.5 – 3.8 MHz | Short wave | Regional traffic, evening |
| 40 m | 7.0 – 7.2 MHz | Short wave | Long-distance traffic, DX |
| 20 m | 14.0 – 14.35 MHz | Short wave | International DX traffic (FT8!) |
| 2 m | 144 – 146 MHz | VHF | Local traffic, repeater operation, satellites, APRS |
| 70 cm | 430 – 440 MHz | UHF | Local traffic, ATV, repeaters — close to TETRA |
DCF77 (77.5 kHz) transmits the official time signal of the PTB Braunschweig. Receivable with a simple SDR receiver and decoder software — a good starter project.
Next: TETRA & emergency-services digital radio →