Hackaday Prize Finalist: A PortableSDR

The popular Hackaday blog is having a contest where contestants submit homemade prototypes of opensource devices they have created. The prize is a trip to space and the winner will be awarded to the best example of an open, connected device. The finalists were recently announced and a device called the PortableSDR is one of them.

The PortableSDR is a portable rugged standalone software defined radio transceiver with a 0 to 30 MHz tuning range (also 144 MHz). A standalone SDR means that no computer is required to use the radio, and can work in a similar way to a standard handheld hardware radio. Its advantages come from its SDR design, which allow it to have a wide tuning range, be able to easily decode most protocols and to also work as an antenna analyzer or vector network analyzer.

Some people have been calling this radio a Baofeng UV-5R killer, which is very high praise as the Baofeng is one of the most popular low cost hardware radios out there.

Nooelec Now Selling RTL-SDR’s with the R820T2 Tuner

Nooelec have recently begun selling RTL-SDR dongles with the R820T2 tuner chip in them. The R820T2 is a small upgrade over the R820T as it has slightly better overall sensitivity (seems to be around 2-6 dB better). Another advantage to the R820T2 is that Oliver Jowett’s experimental driver for HF reception works much better with this chip. The reason is that the R820T2 has wider IF filter bandwidths which improves the mechanism that the experimental driver uses to obtain HF frequencies.

Previously, we posted about a Japanese RTL-SDR experimenter who replaced the R820T chip in a standard dongle with a R820T2 chip and also saw improved sensitivity.

The recently available for preorder Airspy software defined radio also uses the R820T2 tuner in its design.

Nooelec R820T2 RTL-SDR Dongle
Nooelec R820T2 RTL-SDR Dongle

Demo of a New R820T Driver with extra Gain, Decimation and IF Filter Adjustments

Over on YouTube user mm6dos has uploaded a video showing a new driver he helped develop for the R820T tuner which is used in the most commonly purchased RTL-SDR dongles. He writes:

A short demonstration of a new non-gpl RTL2832U / R820T driver specifically written for SDR#. The R820T tuner actually contains a configurable IF filter and 3 separate gain stages. Unfortunately Osmocom’s implementation has fixed this filter and one of the gain stages. Aliasing and overloading is significantly reduced using this driver.

Currently we don’t have a source for the download of this driver, but we assume that it will be released soon. The videos below show the driver in action, with the first video showing the IF filter adjustments and the second video showing the software decimation feature.

RTL# / R820T IF Filter Demo

SDR# RTL# / R820T

Receiving Dead Satellites with the RTL-SDR

Recently happysat, a reader of RTL-SDR.com wrote in to let us know about an unusual hobby he has found with the RTL-SDR. Happysat has been using the RTL-SDR together with a QFH antenna to detect old decommissioned satellites in the 136-138 MHz and 150-400 MHz frequency ranges.

Although these satellite’s batteries have long been expired, because of some sort of chemical reaction due to thousands of failed recharge cycles the batteries begin to conduct over time and allow the satellite to be powered directly from the solar panels thus activating the transmitter.

Happysat writes:

During weathersat reception of NOAA/Meteor on the 137 MHz band i did see quite often unidentified interrupting signals. After a bit of Googling around I learned that these were Dead Satellite’s that still are broadcasting given the right sunlight conditions, the signal strength is sufficient to show up in SDRSharp, not all signals are very strong some very weak and needed a good close up zoom in SDRSharp.

There are many shutdown Satellite’s who apparently having a life of their own varying from Military, Navigation, Experimental, Weather, and also Amateur ones.

Most are not transmitting any usable telemetry or weather images but they still use the original frequencies to sent out a unmodulated carrier, which interferes with the current operational Satellite’s in the 136/138 MHz band.
Normally when a satellite goes out of service and runs almost out of fuel the last reserve is used to shift it in a graveyard orbit which resides above the normal operation orbit, it will be switched off and left on their own.

But this will not always goes as planned, sometimes due solar radiation or other technical failures it will not respond again to the ground station commands, which leaves the Satellite in its current orbit. Some have a timer onboard which will be activated at end of life scheduled to end/shortcut the power feed to the transmitter so it will not broadcast again, also this can fail.

Until some day they might not work at all anymore..

But that can take a while one of the oldest satellite still broadcasting are:

Transit 5B-5 (Military Navigation) from 1964 – they can be heard in either CW or USB mode. An audio example of Transit is over here [link to example] (my recording – link to online stream  uploaded by commenter Jordan here) it sounds like some kind of melody song.

And LES-1 from 1965 (Lincoln Experimental Satellite 1)
Audio example over here [link to example] thanks to Phil Williams.

Others are just a spooky hauling sound like LES-1, NOAA’s etc due the Voltage fluctuation from the solar panels.

DD1US does have a very nice collection images and orginal sounds on : [space sounds]

A list of frequencies and more in depth details can be found on Mike Kenny’s excellent website: [mike kenny’s website]

My TLE containing all current Deadsatellite’s is available on dropbox for anyone would like to try out – [TLE file]
Updated once a week.

You can use it in your favorite tracker, i prefer Gpredict for this course of the unstable frequency and Doppler effects Orbitron will not always suite on this birds.

Happysat has also provided a frequency database for SDR# containing the frequencies of all the dead satellites.

Transit 5B
Transit 5B
Transit 5B
Transit 5B
Fenyung 1D
Fenyung 1D

Radio Astronomy using a Differential Radiometer and Interferometer with an RTL-SDR

Amateur radio astronomer Marcus Leech often makes use of RTL-SDR dongles for his amateur radio astronomy experiments. Recently Marcus wrote a technical paper discussing a modern SDR implementation of a Dicke Radiometer, which is a type of radio telescope that is designed to significantly reduce the effects of receiver noise. Marcus has also developed an RTL-SDR approach to another similar system called the Phase-Switched Interferometer.

Using his new SDR based approach together with GNU Radio, a 10ft satellite dish and two RTL-SDR dongles he was able to plot a transit of the Milky Way Galaxy as shown below.

Milky Way Galaxy Transit
Milky Way Galaxy Transit

Airspy Now Available for Pre-Order (Shipping Mid November)

The long awaited Airspy software defined radio is now available for preorder and will ship during mid November for those orders placed before November 7. It is priced at $199 USD.

The Airspy is an RX only SDR with a tuning range of 24 MHz to 1.7 GHz, up to 10 MHz of instantaneous bandwidth and a 12-bit ADC. The full list of features is shown below. If you are looking for an upgrade to the RTL-SDR and do not need TX capabilities, this is probably the SDR that will provide the best performance for price.

  • Continuous 24 – 1750 MHz RX range with no gaps
  • 3.5 dB NF between 42 and 1002 MHz
  • Tracking RF filters
  • 35dBm IIP3 RF front end
  • 12bit ADC @ 20 MSPS (80dB Dynamic Range, 64dB SNR, 10.4 ENOB) – Yeah, size does matter.
  • Up to 80 MSPS for custom applications
  • Cortex M4F @ up to 204MHz with Multi Core support (dual M0)
  • 1.5 ppm high precision, low phase noise clock
  • 1 RTC clock (for packet time-stamping)
  • External clock input (10 MHz to 100 MHz via MCX connector) – Ideal for phase coherent radios
  • 10 MHz panoramic spectrum view with 9MHz alias/image free
  • IQ or Real, 16bit fixed or 32bit float output streams
  • No IQ imbalance, DC offset or 1/F noise at the center of the spectrum that plagues all the other SDRs
  • Extension ports: 16 x SGPIO
  • 1 x RF Input (SMA)
  • 1 x RF Output (Loopthrough, U-FL)
  • 2 x High Speed ADC inputs (up to 80 MSPS, U-FL)
  • 4.5v software switched Bias-Tee to power LNA’s and up/down-converters

See our big comparison list of other SDRs here.

Airspy Software Defined Radio
Airspy Software Defined Radio

New Raspberry Pi Image with RTL-SDR Drivers and GNU Radio Built In

A new image for the Raspberry Pi containing RTL-SDR software has been made available by tech enthusiast Gareth Hayes. The image contains all the software and drivers needed to get started with the RTL-SDR or HackRF on a 512MB Raspberry Pi. It is very useful as compilation of large software like GNU Radio is slow and problematic on an embedded PC like the Raspberry Pi. The image contains the following software:

  • GNU Radio V3.7.5 built from source, including GNU Radio Companion
  • Osmocom GNU Radio Source (and Sink) Blocks
  • Support for DVB-T USB dongles
  • Support for HackRF One (and Jawbreaker)
  • RTL-SDR Suite
  • Gqrx

A few months ago we also featured a similar image for the BeagleBone Black.

Raspberry Pi Mini Linux Computer
Raspberry Pi Mini Linux Computer

Shielding the RTL-SDR

Over on Reddit user will1384 has posted about his imgur photo album that clearly documents some well researched steps that he took in an effort to shield the RTL-SDR dongle from interference. Interference is caused by strong out of band signals that can sometimes show up even when no antenna is connected to the dongle. Shielding the dongle helps to remove this interference.

The main steps he took were the following:

  1. Buy an aluminium case from ebay and put the dongle inside it.
  2. Remove the USB connector and ground the dongle ground to the aluminium casing using a 1M Ohm resistor and a 47nf ceramic disk capacitor.
  3. Connect the USB data lines to a USB extension cable and wrap a toroid around the 5v and GND lines and twist the two data lines together.

There is a discussion about this shielding project on Reddit.

Shielding Wiring Diagram
Shielding Wiring Diagram

Receiving Hellschreiber with the RTL-SDR and an Upconverter

Over on YouTube user BSoD Badgers has uploaded a video showing reception of Hellschreiber on HF at 20m. To receive the HF frequencies he used a ham-it-up upconverter. He used SDR# to receive the signal and the Fldigi decoding software to decode the signal.

Hellschreiber is a fax-like communications mode used by amateur radio hobbyists.

Hellschreiber 20M

RF Analyzer Android App for the HackRF

Earlier this month we posted about a new port of the HackRF software defined radio Linux library for Android. Now the author of the Android port has created a new app called RF Analyzer. The app is basically a real time spectrum viewer that includes a waterfall display. The app can be downloaded from Github at https://github.com/demantz/RFAnalyzer.

The app currently supports the following features.

  • Browse the spectrum by scrolling horizontally
  • Zoom in and out, both horizontally and vertically
  • Adjust the sample rate and center frequency to match the current view of the screen by double tapping
  • Auto scale the vertical axis
  • Jump directly to a frequency
  • Adjust the gain settings of the HackRF
  • Select a pre-recorded file as source instead of a real HackRF
  • Change the FFT size
  • Setting the frame rate either to a fixed value or to automatic control
  • Activate logging and showing the log file

In the future the author intends to support the RTL-SDR and implement demodulation for basic modes such as AM, FM and SSB.

To use the app you’ll need an USB OTG (on-the-go) cable to connect your Android device to the HackRF.

RF Analyzer Android App for the HackRF
RF Analyzer Android App for the HackRF
RF Analyzer demonstration – Showing a FFT plot by using an Android device and the HackRF