Category: RTL-SDR

rtlmic: Wireless Microphone Receiver for RTL-SDR

Over on GitHub a new program called rtlmic has recently been uploaded. The program descriptions reads: 

rtlmic is a multichannel FM microphone receiver/demodulator for RTL-SDR cards. It outputs realtime audio to JACK.

Basic usage is simply:

$ rtlmic [channel 1 frequency] [channel 2 frequency]…

This program may be able to be used as a replacement for wireless microphone base stations at events. The software allows you to capture as many channels as your CPU can handle, within the active bandwidth of the RTL-SDR. There are also settings for tweaking the companding ratio and tau, deemphasis tau and FM deviation all of which affect the output audio and can be used to optimize the frequency response of the microphone.

The audio outputs directly to Jack audio which is an audio piping API, which simply routes the audio out to wherever you choose it to go.

A typical wireless microphone base station and microphones.
A typical wireless microphone base station and microphones.

CNxROOT Two Posts: How to Build an RTL-SDR Server with OpenWRT, Creating a GSM BaseStation with OpenBTS and a USRP

Recently security researcher cnxroot wrote in to let us know about two of his posts that may be of interest to readers. The posts are written in Chinese, so please use Google Translate to read them in English – it translates okay to some extent.

The first post shows us how to run the RTL-SDR on an OpenWRT capable router server. OpenWRT is a Linux firmware/OS that can be installed on several compatible router devices which extends the usefulness and features of the router. Since it is running Linux the RTL-SDR drivers can be installed onto it, and then rtl_tcp can be run, providing a remote RTL-SDR.

The second post is a bit more advanced. It is about creating a pseudo GSM base station with a USRP SDR and intercepting IoT devices which connect over GSM/GPRS. The post shows how to set up OpenBTS which can be used to create a base station.

RTL-SDR running on an internet router with OpenWRT.
RTL-SDR running on an internet router with OpenWRT.

A Homemade PCB Log-Periodic Antenna

Ham radio enthusiast and RF designer Marco Cardelli (IZIOW) recently wrote in and wanted to share his PCB log periodic antenna design which he has been using together with RTL-SDR dongles. Log periodic’s are very wideband directional antennas that can easily be printed onto a circuit board.

Marco’s antenna covers a frequency range of 900 MHz – 2600 MHz.  The original principal focus was for EMI/EMC measurements, but Marco writes that it works perfectly fine for microwave experiments on the 23 and 13cm bands of wi-fi links. Marco currently uses this antenna for reception of microwave beacons. Currently there are no designs or plans on his website for the antenna, but we suspect that he will put them up soon.

If you’d rather purchase an antenna like this instead building one, then we’ve seen in the past good reviews from the PCB antennas available from wa5vjb at www.wa5vjb.com.

The wideband PCB log-periodic antenna.
The wideband PCB log-periodic antenna.
Return Loss of the PCB Log Periodic antenna.
Return Loss of the PCB Log Periodic antenna.

Radio For Everyone New Posts: Building an ADS-B Station, Easy Homemade Beginner ADS-B Antennas

Akos the author of the radioforeveryone.com blog has recently added two new articles to his blog. The first post is a comprehensive guide to setting up your own ADS-B station. The guide focuses on creating a system that is easy to use, has good performance and is value for money. In the post he shows what type of computing hardware is required, what software can be used and what RTL-SDR dongles work best. He also shows what choices are available when it comes to amplification and filtering to improve signal reception and goes on to talk a bit about adapters and the antennas that work best for him.

BuildingADS-Bstation
Building a ADS-B station

 In the second post Akos shows more on how to build your own beginners antennas for ADS-B reception. The post focuses on showing how to modify the stock magnetic mount antenna that comes with most RTL-SDR dongles, and how to build a half-wave ‘spider’ antenna entirely out of coax cable. The post is full of easy to follow images which make it great for beginners.

EDIT: It’s been pointed out in the comments by antenna experts/enthusiasts that the 1/2 wave ground plane antenna described by Akos in his tutorial may not be technically correct. A 1/2 wave antenna has a huge impedance which requires some sort of matching. Without matching there is going to be about 10 dB of loss due to the mismatch, and so the antenna will perform poorly. We recommend sticking with a 1/4 wave design, which is essentially the same as Akos’ 1/2 wave ground plane antenna, just with the element lengths halved.

Running a 1G Mobile Phone Network with a HackRF

First generation (1G) mobile phone technology was brought out in the 80’s and was an unsecured analogue system. These days 1G technology is completely phased out in favor of digital standards like 2G (GSM), 3G and 4G LTE and so those old 1G handsets are now useless. However, at Shmoocon 2017 presenter Brandon Creighton delivered a talk where he showed how to use a TX capable SDR like a USRP or HackRF to create your own home 1G system that allows those old brick phones to be useful once again.

The actual video of the conference talk won’t be available online until about half way through the year but the blurb read:

AMPS, the first widely deployed cellular network in the US, was old enough that it had been designed by pre-breakup Bell, yet robust enough to survive for decades in service. Unlike LTE or even GSM, it was also a protocol simple enough to be described in a fairly short specification; if you wanted to you could listen to calls with a TV tuner (or modified phone).

This is a talk on the design and implementation of gr-amps, a set of GNU Radio blocks that can turn a TX-capable software-defined radio into a base station for AMPS devices–including that brick phone in your basement. No background in SDR is necessary to follow along (but it doesn’t hurt).

Expect detours into near-forgotten phreaker history: the weaknesses that enabled phone cloning, the efforts of wireless carriers and the US government to fight exploitation, and more.

The GNU Radio code to run your own AMPS (1G) system is available on GitHub.  It has been tested on a USRP and HackRF.

lethalweaponcellphone

[Also seen on Hackaday]

Hacking a Danfoss Wireless Thermostat with an RTL-SDR

Over on his blog Andy writes how he wanted a smart way to control his central heating system with a Raspberry Pi and Arduino microcontroller. He discovered that if he could reverse engineer his existing wireless thermostat then he would have an easy way to control the boiler in his house and with that a smart controller could be made. By reverse engineering the thermostat he also avoids the need to rig up his own control system.

The existing thermostat wireless receiver is a Danfoss RX2. In order to reverse engineer the protocol Andy opened up an older that one he had and saw that it used an Infineon TDA5210 RF receiver chip. Armed with this part number he was able to look up the datasheet and determine the operating frequency. Then by using an RTL-SDR he captured some packets while pressing buttons on the thermostat transmitter and piped the audio file into audacity, where he was able to clearly see the digital waveform.

Andy then wrote a Python program using the ‘wave’ library, which allowed him to easily read binary values for a .wav file. With his code he was able to extract the data from the signal and determine the preamble, sync word, thermostat ID and the instruction code (on/off/learn).

In a future post Andy hopes to show us how he’ll use an RF69 module with an Arduino to actually control the thermostat using the reverse engineered packet knowledge.

Danfoss Wireless Thermostat and a Received Binary Waveform in Audacity
Danfoss Wireless Thermostat and a Received Binary Waveform in Audacity

Radio For Everyone New Posts: Line of Sight, Why USB Cable Quality Matters, Uputronics 1090 MHz Filtered Preamp Review

Over on his radioforeveryone.com blog, author Akos has uploaded three new posts. The first post briefly explains visually what is meant by line of sight when it comes to radio signals. Essentially at UHF and higher frequencies the radio antenna needs to be able to ‘see’ the transmitter, meaning that any blockages such as trees, houses etc will block the signal.

In his second post Akos briefly explains why USB cable quality can matter when it comes to SDRs. He shows that some USB cables tend to pick up more interference than others. 

Finally in his third post Akos reviews the Uputronics 1090 MHz Filtered Preamp. Uputronics is a UK based company that sells various filtered LNA’s. Akos writes how he’s very impressed with the premium packaging, look and feel of the device and thickness of the metal case. In performance tests the preamp together with a V3 dongle with bias tee power clearly improves ADS-B position reports significantly. We note that we also have 1090 MHz filtered preamp from Uputronics (an older model), and can also highly recommend their products.

The Uputronics 1090 MHz Filtered Preamp reviewed on radioforeveryone.
The Uputronics 1090 MHz Filtered Preamp reviewed on radioforeveryone.com

Lowering the Noise Floor on HF with High Quality Coax

Bonito is a company that sells various products such as their own small active antennas. Some examples are the Bono-Whip (20kHz – 300 MHz), GigaActiv (9kHz – 3 GHz) and the MegaLoop (9kHz – 200 MHz). 

Over on their blog they’ve uploaded a post titled “why even good antennas need good coax cable”. The post explains why high quality heavy shielded coax cable may be required to receive HF signals in noisy environments. The author writes how even placing an antenna in a quiet area outdoors may not work if the coax is still run through an high interference environment, such as through a house.

Typically RG58 cable is most commonly used with HF antennas. However, the author noticed that when using RG58 he was still receiving FM stations, even though the antenna that he was using was a MegaLoop with a built in broadcast FM filter. After switching his RG58 cable to H155 coax, the FM station disappeared. H155 coax is low loss and designed for GHz level frequencies, so it has much better shielding from its tighter braid.

The images below also show the difference in noise floor the author saw after replacing all his RG58 with H155 coax. 

http://ReceptionwithRG58Coax

Reception with RG58 Coax

http://ReceptionwithH155Coax

Reception with H155 Coax

rtlmic: Wireless Microphone Receiver for RTL-SDR

Over on GitHub a new program called rtlmic has recently been uploaded. The program descriptions reads: 

rtlmic is a multichannel FM microphone receiver/demodulator for RTL-SDR cards. It outputs realtime audio to JACK.

Basic usage is simply:

$ rtlmic [channel 1 frequency] [channel 2 frequency]…

This program may be able to be used as a replacement for wireless microphone base stations at events. The software allows you to capture as many channels as your CPU can handle, within the active bandwidth of the RTL-SDR. There are also settings for tweaking the companding ratio and tau, deemphasis tau and FM deviation all of which affect the output audio and can be used to optimize the frequency response of the microphone.

The audio outputs directly to Jack audio which is an audio piping API, which simply routes the audio out to wherever you choose it to go.

A typical wireless microphone base station and microphones.
A typical wireless microphone base station and microphones.

CNxROOT Two Posts: How to Build an RTL-SDR Server with OpenWRT, Creating a GSM BaseStation with OpenBTS and a USRP

Recently security researcher cnxroot wrote in to let us know about two of his posts that may be of interest to readers. The posts are written in Chinese, so please use Google Translate to read them in English – it translates okay to some extent.

The first post shows us how to run the RTL-SDR on an OpenWRT capable router server. OpenWRT is a Linux firmware/OS that can be installed on several compatible router devices which extends the usefulness and features of the router. Since it is running Linux the RTL-SDR drivers can be installed onto it, and then rtl_tcp can be run, providing a remote RTL-SDR.

The second post is a bit more advanced. It is about creating a pseudo GSM base station with a USRP SDR and intercepting IoT devices which connect over GSM/GPRS. The post shows how to set up OpenBTS which can be used to create a base station.

RTL-SDR running on an internet router with OpenWRT.
RTL-SDR running on an internet router with OpenWRT.

A Homemade PCB Log-Periodic Antenna

Ham radio enthusiast and RF designer Marco Cardelli (IZIOW) recently wrote in and wanted to share his PCB log periodic antenna design which he has been using together with RTL-SDR dongles. Log periodic’s are very wideband directional antennas that can easily be printed onto a circuit board.

Marco’s antenna covers a frequency range of 900 MHz – 2600 MHz.  The original principal focus was for EMI/EMC measurements, but Marco writes that it works perfectly fine for microwave experiments on the 23 and 13cm bands of wi-fi links. Marco currently uses this antenna for reception of microwave beacons. Currently there are no designs or plans on his website for the antenna, but we suspect that he will put them up soon.

If you’d rather purchase an antenna like this instead building one, then we’ve seen in the past good reviews from the PCB antennas available from wa5vjb at www.wa5vjb.com.

The wideband PCB log-periodic antenna.
The wideband PCB log-periodic antenna.
Return Loss of the PCB Log Periodic antenna.
Return Loss of the PCB Log Periodic antenna.

Radio For Everyone New Posts: Building an ADS-B Station, Easy Homemade Beginner ADS-B Antennas

Akos the author of the radioforeveryone.com blog has recently added two new articles to his blog. The first post is a comprehensive guide to setting up your own ADS-B station. The guide focuses on creating a system that is easy to use, has good performance and is value for money. In the post he shows what type of computing hardware is required, what software can be used and what RTL-SDR dongles work best. He also shows what choices are available when it comes to amplification and filtering to improve signal reception and goes on to talk a bit about adapters and the antennas that work best for him.

BuildingADS-Bstation
Building a ADS-B station

 In the second post Akos shows more on how to build your own beginners antennas for ADS-B reception. The post focuses on showing how to modify the stock magnetic mount antenna that comes with most RTL-SDR dongles, and how to build a half-wave ‘spider’ antenna entirely out of coax cable. The post is full of easy to follow images which make it great for beginners.

EDIT: It’s been pointed out in the comments by antenna experts/enthusiasts that the 1/2 wave ground plane antenna described by Akos in his tutorial may not be technically correct. A 1/2 wave antenna has a huge impedance which requires some sort of matching. Without matching there is going to be about 10 dB of loss due to the mismatch, and so the antenna will perform poorly. We recommend sticking with a 1/4 wave design, which is essentially the same as Akos’ 1/2 wave ground plane antenna, just with the element lengths halved.

Running a 1G Mobile Phone Network with a HackRF

First generation (1G) mobile phone technology was brought out in the 80’s and was an unsecured analogue system. These days 1G technology is completely phased out in favor of digital standards like 2G (GSM), 3G and 4G LTE and so those old 1G handsets are now useless. However, at Shmoocon 2017 presenter Brandon Creighton delivered a talk where he showed how to use a TX capable SDR like a USRP or HackRF to create your own home 1G system that allows those old brick phones to be useful once again.

The actual video of the conference talk won’t be available online until about half way through the year but the blurb read:

AMPS, the first widely deployed cellular network in the US, was old enough that it had been designed by pre-breakup Bell, yet robust enough to survive for decades in service. Unlike LTE or even GSM, it was also a protocol simple enough to be described in a fairly short specification; if you wanted to you could listen to calls with a TV tuner (or modified phone).

This is a talk on the design and implementation of gr-amps, a set of GNU Radio blocks that can turn a TX-capable software-defined radio into a base station for AMPS devices–including that brick phone in your basement. No background in SDR is necessary to follow along (but it doesn’t hurt).

Expect detours into near-forgotten phreaker history: the weaknesses that enabled phone cloning, the efforts of wireless carriers and the US government to fight exploitation, and more.

The GNU Radio code to run your own AMPS (1G) system is available on GitHub.  It has been tested on a USRP and HackRF.

lethalweaponcellphone

[Also seen on Hackaday]

Hacking a Danfoss Wireless Thermostat with an RTL-SDR

Over on his blog Andy writes how he wanted a smart way to control his central heating system with a Raspberry Pi and Arduino microcontroller. He discovered that if he could reverse engineer his existing wireless thermostat then he would have an easy way to control the boiler in his house and with that a smart controller could be made. By reverse engineering the thermostat he also avoids the need to rig up his own control system.

The existing thermostat wireless receiver is a Danfoss RX2. In order to reverse engineer the protocol Andy opened up an older that one he had and saw that it used an Infineon TDA5210 RF receiver chip. Armed with this part number he was able to look up the datasheet and determine the operating frequency. Then by using an RTL-SDR he captured some packets while pressing buttons on the thermostat transmitter and piped the audio file into audacity, where he was able to clearly see the digital waveform.

Andy then wrote a Python program using the ‘wave’ library, which allowed him to easily read binary values for a .wav file. With his code he was able to extract the data from the signal and determine the preamble, sync word, thermostat ID and the instruction code (on/off/learn).

In a future post Andy hopes to show us how he’ll use an RF69 module with an Arduino to actually control the thermostat using the reverse engineered packet knowledge.

Danfoss Wireless Thermostat and a Received Binary Waveform in Audacity
Danfoss Wireless Thermostat and a Received Binary Waveform in Audacity

Radio For Everyone New Posts: Line of Sight, Why USB Cable Quality Matters, Uputronics 1090 MHz Filtered Preamp Review

Over on his radioforeveryone.com blog, author Akos has uploaded three new posts. The first post briefly explains visually what is meant by line of sight when it comes to radio signals. Essentially at UHF and higher frequencies the radio antenna needs to be able to ‘see’ the transmitter, meaning that any blockages such as trees, houses etc will block the signal.

In his second post Akos briefly explains why USB cable quality can matter when it comes to SDRs. He shows that some USB cables tend to pick up more interference than others. 

Finally in his third post Akos reviews the Uputronics 1090 MHz Filtered Preamp. Uputronics is a UK based company that sells various filtered LNA’s. Akos writes how he’s very impressed with the premium packaging, look and feel of the device and thickness of the metal case. In performance tests the preamp together with a V3 dongle with bias tee power clearly improves ADS-B position reports significantly. We note that we also have 1090 MHz filtered preamp from Uputronics (an older model), and can also highly recommend their products.

The Uputronics 1090 MHz Filtered Preamp reviewed on radioforeveryone.
The Uputronics 1090 MHz Filtered Preamp reviewed on radioforeveryone.com

Lowering the Noise Floor on HF with High Quality Coax

Bonito is a company that sells various products such as their own small active antennas. Some examples are the Bono-Whip (20kHz – 300 MHz), GigaActiv (9kHz – 3 GHz) and the MegaLoop (9kHz – 200 MHz). 

Over on their blog they’ve uploaded a post titled “why even good antennas need good coax cable”. The post explains why high quality heavy shielded coax cable may be required to receive HF signals in noisy environments. The author writes how even placing an antenna in a quiet area outdoors may not work if the coax is still run through an high interference environment, such as through a house.

Typically RG58 cable is most commonly used with HF antennas. However, the author noticed that when using RG58 he was still receiving FM stations, even though the antenna that he was using was a MegaLoop with a built in broadcast FM filter. After switching his RG58 cable to H155 coax, the FM station disappeared. H155 coax is low loss and designed for GHz level frequencies, so it has much better shielding from its tighter braid.

The images below also show the difference in noise floor the author saw after replacing all his RG58 with H155 coax. 

http://ReceptionwithRG58Coax

Reception with RG58 Coax

http://ReceptionwithH155Coax

Reception with H155 Coax