Decoding Digital Voice (P25, DMR, NXDN, D-STAR) with DSD+

Learn how to decode digital voice communications like APCO P25, DMR MotoTRBO, NXDN and D-STAR with DSD+ and an RTL-SDR dongle.

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Receiving Meteor-M N2 LRPT Weather Satellite Images

The Meteor-M N2 is a polar orbiting Russian weather satellite. With an RTL-SDR an appropriate antenna, you can receive and decode its image downlink and download LRPT weather satellite images.

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Receiving NOAA Weather Satellite Images

Everyday multiple NOAA weather satellites pass above you. Each NOAA weather satellite broadcasts an Automatic Picture Transmission (APT) signal, which contains a live weather image of your area. The RTL-SDR dongle combined with a good antenna, SDRSharp and a decoding program can be used to download and display these live images several times a day.

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Following Trunked Radio with Unitrunker

Follow trunked radio conversations with your RTL-SDR and a program called Unitrunker. Also decode digital communications like P25 and DMR using the Digital Speech Decoder (DSD+) software.

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Decoding DRM Radio

Digital Radio Monodial (DRM) radio is a type of digital shortwave radio signal that is used by international shortwave radio broadcasters. It provides superior audio quality compared to AM signals by using digital audio encoding. With an upconverter, good antenna, and decoding software the RTL-SDR software defined radio can receive and decode DRM signals.

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RTL-SDR for Budget Radio Astronomy

With the right additional hardware, the RTL-SDR software defined radio can be used as a super cheap radio telescope for radio astronomy experiments such as observing the Hydrogen Line and meteor detection.

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Receiving Weather Balloon (Radiosonde) Data with RTL-SDR

Use your RTL-SDR to decode data from weather balloons (aka Radiosondes) that are launched twice daily by meteorological agencies all around the world.

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RTL-SDR Direct Sampling Mode

The RTL-SDR software defined radio can be told to run in a mode called “direct sampling mode”, which with a small hardware mod allows the dongle to tune to the HF frequencies where ham radio and many other interesting signals are found. This means that no upconverter circuit is required.

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Cheap AIS Ship Tracking

Large ships and passenger boats are required to broadcast an identification signal containing position, course, speed, destination, and vessel dimension information to help prevent sea collisions. This system is known as the “Automatic Identification System” or AIS for short. AIS can be decoded with an RTL-SDR dongle and right software.

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Decoding Inmarsat STD-C EGC Messages

With an RTL-SDR dongle, a cheap $10 modified GPS antenna or 1-2 LNA’s and a patch, dish or helix antenna you can listen to Inmarsat satellite signals, and decode the STD-C NCS channel which contains information such as search and rescue (SAR) and coast guard messages as well as news, weather and incident reports.

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RTL-SDR with Forced Air Cooling

Over on his blog, Nobu has uploaded a post showing his experiments with a forced air cooled RTL-SDR dongle (note the blog is in Japanese so use Google Translate). A tiny fan from RS components is attached to the case of the dongle and draws power from the dongles own power regulator. Nobu also replaced the crystal oscillator with a flat packaged oscillator for a better fit.

The translation is a little difficult, but it appears the fan was able to successfully stabilize the temperature. This may be an alternative to the temperature controlled oscillator (TCXO) RTL-SDR modification.

EDIT: It seems that the fan is not to improve temperature stability, but rather to improve sensitivity. Nobu has referenced this experiment which shows that improved heat dissipation improves the dongles sensitivity.

Fan Forced Cooled RTL-SDR
Forced Air Cooled RTL-SDR


  1. steveee

    Ive got mine in an enclosure that cooled by a refrigeration air conditioning unit, I can vouch for increased stability and sensitivity. I use a array of rtl dongles to recieve ads-b data and other radio experiments. Having them sit at a stable temp of 5 – 10 degrees c over a period of time ensures accuracy and minimal degradation of signal.

  2. screamin72

    I’d leave it stock. The max temp these dongles can handle is 160 Fahrenheit, Normally they don’t get that hot. Most of the time 120-140 Fahrenheit recorded. At stable temperature they don’t drift enough to worry about..

  3. CBGoodBuddy

    I’d be worried about electrical and RF noise from the small fan interfering with the sensitive ADC.

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