INDEX
- Briefing
- Spectrum
- Antennas and Filters
- Antenna Types
- Wavelength Calculator
- Frequency Calculator
BRIEFING
Software-defined radio (SDR) is a technology that replaces traditional hardware-based radio components with software.
This post is not meant to be an encyclopedia on SDR, but a landing page with links and references to the most important resources for getting started in the field.
I use the official kit “RTL-SDR Blog V4 RTL2832 1PPM TCXO HF BiasT SMA Software Defined Radio + Antennas” [Link]. Follow along with the vendor’s “Quick Install Guide” [Link].
Datasheet source [Link].
| Tuner Chip | R828D |
| ADC Chip | RTL2832U 8-bits |
| Frequency Range | 500 kHz to 1.766 GHz |
| Bandwidth | 2.56 MHz stable (up to 3.2 MHz with drops) |
| Typical Input Impedance | 50 Ohms |
| Typical Current Draw | 250 to 270 mA |
| HF Implementation | Upconverter with 28.8 MHz LO |
| Input Connector | 1x SMA |
| USB Connector | USB-A Male |
| Local Oscillator Stability | 1PPM TCXO |
| Bias Tee | 4.5V, 180mA (software switchable) |
| Enclosure | Aluminum |
| Heat Dissipation | Thermal Pad to Aluminum Enclosure |
| Front-End RF Design | Triplexor with switchable notch |
| Transmit Capability | None |
SPECTRUM FOR THIS HARDWARE
| MF 500~526.5 kHz | Maritime / Marine Band Distress and emergency (Morse Code), navigation |
| MF 540~1700 kHz | AM Broadcasting Band 10 kHz steps (+/- 5 kHz) Channels: 540, 550, 560… 1700 |
| HF 3~30 MHz | Shortwave AM Broadcasting Radio |
| HF 13.56 MHz | ISM (Industrial, Scientific, and Medical) Band |
| HF 27 MHz | CB (Citizens Band) class D: 10 kHz wide (AM or SSB mode) Unlicensed, 40 channels: 26.965, 26.975… 27.185 |
| HF 40.68 MHz | ISM (Industrial, Scientific, and Medical) Band |
| VHF 50~54 MHz | 6M HAM Band [Link] |
| VHF 54~88 MHz | Digital TV – Channels 2-6 |
| VHF 88~108 MHz | FM Broadcast Band: 200 kHz steps (+/- 100 kHz) Channels: 88.1 MHz, 88.3 MHz… 107.9 MHz |
| VHF 108~137 MHz | Aviation Band (aka “airband”) AM (legacy compatibility) or SSB mode (best) 108 to 117.95 MHz: 200 channels, 50 kHz steps 118 to 136.975 MHz: 760 channels, 25 kHz steps |
| VHF 144~148 MHz | 2M HAM Band [Link] ARISS-SSTV at 145.8 MHz NFM [Link] [Link] |
| VHF 156~174 MHz | Marine Band (aka “Maritime”) 28 channels with 50 kHz step Or 88 channels with 25 kHz steps |
| VHF 161~161.45 MHz | Railways in the US and Canada |
| VHF 162.4~162.55 MHz | NOAA Weather Radio (weather, alerts, and emergency) 8 channels, 25 kHz step, Narrow FM modulation. Channels: 162.400 MHz, 162.425 MHz… 162.550 MHz Alerts preceded by a 1050 Hz attention tone for 10 sec [Link] |
| VHF 174~216 MHz | Digital TV – Channels 7-13 |
| VHF 222~225 MHz | 1.35M HAM Band [Link] |
| UHF 433 MHz | ISM (Industrial, Scientific, and Medical) Band Centered at 433.92 MHz, channels with 25 kHz step. |
| UHF 470~512 MHz UHF 614~890 MHz |
Digital TV Channels 14-20 and 38-83 respectively. Channel 37 (608~614 MHz) is reserved for radio astronomy. |
| UHF 915 MHz | ISM (Industrial, Scientific, and Medical) Band Modulation varies by application: CSS, FSK, QAM… Usage: LoRa, ZigBee, RFID, Sensors, Remotes… |
| UHF 1227.60 MHz UHF 1575.42 MHz |
GNSS (Global Navigation Satellite System) [Link] GPS L2 and L1 frequencies respectively (BPSK modulation). Also used by Galileo (EU), GLONASS (RU), and BeiDou (CN). |
| UHF 1660~1670 MHz | GOES Weather Satellite [Link] Transmission of high-resolution meteorological images. |
| UHF 1698~1707 MHz | NOAA Weather Satellite [Link] Transmission of high-resolution meteorological images. |
ANTENNAS AND FILTERS
The RTL-SDR kit can easily tune into FM stations out of the box, but is unlikely to receive decent-quality AM stations. The reason is that the spectrum is crowded with noise and interference.
Two dipole (half-wave) antennas are included in the kit:
- Telescopic 46-198 cm
- Ranges from 75 MHz to 325 MHz.
- Covers most of the VHF Band:
- FM Broadcast
- Aviation
- Marine
- NOAA Weather Radio
- Military Aviation
- Telescopic 14-30 cm
- Ranges from 500 MHz to 1 GHz.
- Covers part of the UHF Band:
- TV Channels
- Radio astronomy
- Mobile broadband
- ISM (e.g. 433/915 MHz remote controllers/RFIDs)
- Industrial (e.g. SCADA)
- Pagers
- Aeronautical radionavigation
Antenna quality directly determines reception quality for the entire circuit.
The best approach is to choose an antenna that precisely matches the target signal from the start. Building your own antennas is also worth considering.
As an example, see the block diagram of a dual-conversion heterodyne receiver:
- Antenna
- Captures raw incoming RF signals. Must be sized for the target frequency.
- BPF1
- A Band-Pass Filter that selects a specific frequency band (e.g. AM Band, FM Band).
- LNA
- Amplifies weak signals while introducing minimal noise, ensuring sufficient signal strength for further processing.
- BPF2
- Removes unwanted image frequencies to prevent interference during mixing.
- First Mixer
- Mixes the signal with a local oscillator signal to produce a first intermediate frequency (IF1).
- BPF3
- Filters the IF1 signal to select the desired channel (e.g. a radio station), reducing interference from adjacent signals.
- Second Mixer
- Mixes the filtered IF1 signal with a second local oscillator signal, converting it to a lower second IF (IF2) or baseband.
- BPF4
- Filters the final IF2 signal so that only the desired channel passes through for a cleaner output.
- Output
- The final signal, ready to be demodulated to extract audio or data.
MOST POPULAR ANTENNA TYPES
A monopole antenna is a half-dipole vertical rod. The most common type is a quarter-wavelength tall, the minimum height for self-resonance.
A whip antenna is used on mobile and portable radios in the VHF and UHF bands, such as FM radio.
A normal-mode helix (aka “rubber ducky”) is the most common antenna for portable two-way radios due to its small size.
Full-wave loop antennas have the highest radiation resistance, and therefore the highest efficiency of all antenna types.
WAVELENGTH CALCULATION FROM FREQUENCY
Hz
Full Wavelength: – m
1/2 Wavelength: – m
1/4 Wavelength: – m
A half wavelength is a common rule of thumb for the length of a simple antenna to achieve optimal reception.
FREQUENCY CALCULATION FROM ANTENNA LENGTH
m
Frequency: – Hz
Frequency if 1/2 wavelength: – Hz
Frequency if 1/4 wavelength: – Hz
SEE ALSO
SDR Tips and Tricks [Link]
Linux Tools for SDR [Link]