December 28, 2015

CANFI: Cheap Automatic Noise Figure Indicator Updated to V2.7

Back in July 2014 we posted about the CANFI (Cheap Automatic Noise Figure Indicator) system. The CANFI system is a set of hardware components that include an RTL-SDR and a corresponding software program for control. Back then the CANFI system only supported E4000 dongles. However, recently CANFI was updated to version 2.7 and now supports the R820T/2 tuners as well. The documentation has also been heavily improved. The authors of CANFI introduce their system as follows:

One of the main tasks for an experimenting microwave amateur is to measure the Gain (G) and Noise Figure (NF) of a particular receiving device. For this one will need a Noise Figure Indicator and a (calibrated) Noise Source.

There are a number of commercial devices available from different vendors at prices which will exceed an amateur’s budget by many times. A lot of them can be found on the surplus market but this doesn’t help very much. A combination of both meter and noise source is barely sold below the 2.000€ margin.

Since a lot of cheap DVB – T sticks became available the idea was born to use it together with a homebrew noise source as a very cheap alternative to commercial devices [1]. It is now possible to build a suitable solution within a budget of 100 – 200€. Using a PC with USB port for communication and power supply such a device is very compact and almost compatible to an industrial solution. Special software gives a convenient user interface. Last not least you can reuse the DVB-T stick (together with the preamplifier) as a sensitive receiver along with SDR software.

To create a CANFI system you will need an RTL-SDR, a MGZ 30889 preamp, a noise source, a 28V boost converter to power the noise source and a serial to USB converter to control the noise source.

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December 28, 2015

RTLSDR-Airband V2 Released

Back in June of 2014 we posted about the released of a new program called RTLSDR-Airband. RTLSDR-Airband is a Windows and Linux compatible command line tool that allows you to simultaneously monitor multiple AM channels per dongle within the same chunk of bandwidth. It is great for monitoring aircraft voice communications and can be used to feed websites like liveatc.net.

Since our post the development of the software has been taken over by a new developer szpajder, who wrote in to us to let us know that he has now updated RTLSDR-Airband to version 2.0.0. The new versions improves performance and support for small embedded platforms such as the Raspberry Pi 2, but the Windows port is now not actively maintained and probably does not work. The full list of changes is shown below:

New libconfig-style config file format
util/convert_cfg: can be used to convert old-style config.txt to the new format
Syslog logging (enabled by default)
Daemon mode
Reworked makefiles, added install rule
/dev/vcio is now used to access GPU on Raspberry Pi; creating char_dev no longer necessary
Startup scripts for Debian and Gentoo
Support for auto gain setting
Support for multiple outputs per channel
Support for recording streams to local MP3 files
Support for ARMv7-based platforms other than RPi (eg. Cubieboard)
Updated documentation
Numerous bugfixes and stability improvements

Compilation and install instructions can be found on the projects main GitHub page.

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December 28, 2015

Deocoding Orbcomm with MultiPSK 4.31 and an RTL-SDR

MultiPSK is a signals decoding program with many available decoders to choose from. It is also able to directly connect to the RTL-SDR, or be used via a virtual audio cable. The latest beta version (available on the MultiPSK Yahoo mailing list) now allows for decoding of Orbcomm satellites which transmit at around 137 MHz. While it is not possible to decode the encrypted messages, it is still possible to decode pieces of telemetry data from the satellites. MultiPSK writes the following information about Orbcomm:

This system has been developed by the ORBCOMM society which disposes of a constellation of about 28 active LEO (“Low Earth Orbit”) satellites, transmitting between 137.2 and 137.8 MHz (+/- 2.5 KHz maximum of Doppler shift).

This system permits:

to handle messages (encrypted) from ground users
(ships, trucks, oil wells…) until other ground users, through the ORBCOMM satellites, the cover being worldwide. These frames are decoded by Multipsk but not deciphered.

to broadcast identification, frequencies, position and orbital elements pieces of information, not encrypted. These frames are decoded and interpreted by Multipsk.

This mode is available for licencied copies, only (otherwise, the decoding is stopped after 5 minutes).

One user of MultiPSK has uploaded a video showing the Orbcomm decoding in action.

Multipsk 4.31 decoding Orbcomm

Watch this video on YouTube

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December 23, 2015

Signal Direction Finding with an RTL-SDR, Raspberry Pi and REDHAWK

Something we missed posting about from last year was this presentation on “RasHAWK”, a direction finding system (pdf) built out of a Raspberry Pi, an RTL-SDR and four antennas on a 4 way switch running software created with REDHAWK. REDHAWK is a visual DSP development platform that can be considered similar to GNU Radio or some parts of MATLAB. The authors write:

The RasHAWK team has used a Raspberry Pi as the basis for a networked RF sensor capable of supporting spectrum monitoring, signal intercept and direction finding (DF) operations.

Several RasHAWK sensors are deployed in a distributed sensor grid, wirelessly tethered to a command and control (C2) laptop. The system has the following key features and capabilities:

A simple operator interface to configure the sensors

Falling raster and PSD displays to monitor the spectrum for signal activity

Demodulate FM signals from target FRS radios and play audio on selected channels

Perform coarse DF on target emitters

Display a map of the surrounding terrain that is annotated with the positions of the sensors, the target emitter and calculated lines of bearing (LOB) to the target. The map provides a RF Common Operating Picture (COP) with can be viewed on WiFi enabled tablets or smartphones.

Each RawHAWK sensor can determine the bearing of transmitted signal. By combining several networked RasHAWK sensors at different locations they are able to pinpoint the actual location of the transmitter on a map.

Lines of bearings combined from three different RawHAWK sensors.

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December 23, 2015

SDRPlay RSP API Updated to Version 1.8.0

The SDRplay team have recently released a major update to their API and drivers. The new version is 1.8.0 and they write that it should remove the DC offset, reduce in band images from strong signals, and lower the noise floor. The SDRplay is a software defined receiver that costs $149 USD. They write:

We are pleased to announce release 1.8.0 of the API for the RSP. This is a major upgrade to the API with new features and an improved gain map which should result in improved performance over a key portion of the gain control range. Currently this API is available for Windows only, but versions for Linux and Mac OS and Android will follow shortly.

The API now incorporates automatic post tuner DC offset correction and I/Q compensation. This will almost completely eliminate the DC centre spike that was previously present in zero IF mode and also correct for amplitude and phase errors in the I/Q signal paths that can lead to in-band images when strong signals are present.

There is a new gain map for the RSP which should help improve the receiver noise floor for gain reduction settings in the range of 59-78 dB. To achieve this, the IF gain control range has been increased from 59 to 78 dB. In addition, the user can now turn the LNA on or off at any point within the IF gain control range. This means that the LNA can remain on for gain reduction settings of up to 78 dB, whereas previously the maximum gain reduction that could be attained whilst the LNA was on was only 59 dB. Being able to leave the LNA on will result in improvements in the receiver noise performance for gain reductions in the range of 59 to 78 dB. The upper 19 dB of the IF gain control range have now been disabled. In practice this part of the gain control range was useless as trying to operate within this region always lead to receiver overload even when signals were very weak.

To fully exploit the features of this new API release, we have also issued release 3.5 of the ExtIO plugin. This plugin will work with HDSDR, SDR sharp (releases 1361 or earlier) and Studio 1. Automatic I/Q compensation and DC offset correction will work with later versions of SDR sharp, but we will need to update the native plugin for users of these later versions to be access the new gain map.

Similarly, users of SDR Console will gain the benefit of automatic DC offset compensation and I/Q correction, but will not yet be able to access the new gain map. We hope that a version of SDR console that unlocks this feature will become available in the near future.

Until a new release of SDR-Console is available, you can copy the API into the SDR-Console installation directory…

from C:\Program Files\MiricsSDR\API\x64\mir_sdr_api.dll to C:\Program Files\SDR-RADIO-PRO.com\mir_sdr_api.dll

The API installer has also contains an extra certificate to be more user friendly for Windows XP, Vista and Windows 7 users.

The new API and ExtIO plugin can be downloaded from our website at:www.sdrplay.com/windows.html

As they write that in band images from strong signals are reduced in this version we decided to do a quick before and after test using our own RSP receiver. We tuned into some TETRA signals that had exhibited images in the past on our RSP (you can see them as the yellow signals in the before image). In the new driver the images are completely gone.

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December 21, 2015

DEFCON 23 – LTE Recon and Tracking with RTLSDR

Back on Dec 5 we posted about some Defcon 23 talks that were released from the Wireless Village set of talks. Recently some more talks from other tracks have been released and one of interest to our blog is the talk by Ian Kline titled “LTE Recon and Tracking with RTLSDR”. The talk’s blurb reads:

Since RTLSDR became a consumer grade RX device, numerous talks and open source tools enabled the community to monitor airplanes, ships, and cars… but come on, what we really want to track are cell phones. If you know how to run cmake and have $50 to pick up an RTLSDR-E4000, I’ll make sure you walk out of here with the power to monitor LTE devices around you on a slick Kibana4 dashboard. You’ll also get a primer on geolocating the devices if you’ve got a second E4000 and some basic soldering skills.

DEF CON 23 - Ian Kline - LTE Recon and Tracking with RTLSDR

Watch this video on YouTube

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December 21, 2015

Receiving and acquiring GPS positions with an RTL-SDR dongle and GPS antenna

GPS experimenter and blog author e.p. has recently been posting about his experiments in which he uses an RTL-SDR dongle to receive GPS satellite signals and acquire a position lock.

To receive GPS e.p. uses one of our RTL-SDR blog units (back in stock soon!) with the bias tee enabled which is used to power a cheap 5V active GPS antenna. For software he uses GNSS-SDRLIB and RTKLIB which runs on Windows. Using the RTL-SDR, GPS antenna and the decoding software he was able to get his current position to within about 5 meters of accuracy.

In his blog post e.p. shows a step by step guide on how to install and use the Windows software. In later posts he also shows how to install and use another program called GNSS-SDR which runs in Linux and can also be used to acquire GPS fixes with an RTL-SDR dongle.

To illustrate the software in action e.p. has also uploaded a video to YouTube which is shown below.

Watch this video on YouTube

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December 17, 2015

SvxLink Now Supports the RTL-SDR

SvxLink is an EchoLink and general purpose voice services system for controlling ham radio repeaters. A repeater is a radio tower that receives a weak transmission from a handheld or remote radio and then repeats the same message with greater power over a wide area. With repeaters radio communications can cover a much further distance.

Ham radio enthusiasts often set up repeaters for their own frequencies, so that they can be heard over a wider range. To control the repeater software like SvxLink is required. In the latest software update of SvxLink they added RTL-SDR support. They write:

The biggest news in this release is the support for RTL2832U based DVB-T USB dongles. This make it possible to use such USB dongles as cheap SDR (Software Defined Radio) receivers. This will open up the world of cheap receiver hardware to all SvxLink users. It will for example be very cheap to set up an extra receiver with local coverage for a SvxLink based repeater, as long as there is a network connection to the repeater. The modulation forms supported are: FM, FM narrow, AM, AM narrow, USB, LSB, CW, CW wide and wideband FM (broadcast). Running multiple receivers on the same dongle is supported as well as using multiple dongles.

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