Tagged: rtl-sdr

An RTL-SDR to RTL-SDR QSO with RTL-TRX: Transmit RTTY with the RTL-SDR

Back in 2014 oh2ftg discovered that the RTL-SDR could actually be used to transmit data by modulating leakage from its internal local oscillator. Now it seems that tejeez and oh2ftg have released a new program that makes transmitting with the RTL-SDR easy. The program is called rtl-trx. It runs on Linux and allows you to to transmit RTTY or a simple beacon with the RTL-SDR. The software is available on GitHub at https://github.com/tejeez/rtl-trx. About how it works, the readme says:

Local oscillator leakage from an RTL-SDR dongle can be used as a very low power FSK transmitter. This program transmits RTTY and also makes it easy to use the same dongle to receive RTTY in between transmissions. The goal is to make it possible to have a two-way QSO between two dongles.

Over on YouTube oh2ftg has also uploaded a video that demonstrates the software in action by doing a 1270 MHz RTTY QSO between two modified RTL-SDR dongles. He uses fldigi to decode the RTTY signal and the signal is sent with the following settings: 425 Carrier shift, 45.45 Baud rate, 5 Bits per character, none Parity, 2 Stop bits. 

This previous post shows the hardware modification that can be done to improve the output power. Again, as with the Raspberry Pi transmitters, the output power is very low and probably won’t cause any trouble, but still please do take care if you intend on actually transmitting anything as the output spectrum is probably not very clean.

RTL2RTL QSO! on 1270MHz

SDR4Everyone: Getting Started with the RTL-SDR and SDRUno

Over on his sdr4everyone blog author Akos has uploaded a tutorial that shows how to set up the recently released SDRUno with the RTL-SDR. SDRuno is a spin-off of the (recently acquired by SDRplay) Studio1 software. Although designed and tailored for the SDRplay, SDRuno also supports any radio with an ExtIO interface available, such as the RTL-SDR. The one limitation is that the maximum bandwidth of radios other than the SDRplay is locked to 1 MHz at most.

Akos’ post shows where to download and add the required ExtIO file (it’s the same one used for HDSDR) and how to start the RTL-SDR in SDRuno, as well as a quick tutorial on changing some settings and tuning.

We note that the fact that you need to install the ExtIO dll file to the documents folder seems to be a bug in the latest version at the moment. In future updates they may fix this, and then the ExtIO dll will go back to needing to be added to the C:\Program Files (x86)\SDRplay\SDRuno folder, as it was in previous versions. We’ve also heard one or two reports of users stating that they needed to add in the libusb-1.0.dll file as well, but we can’t confirm if this is actually required as none of our test PC’s have needed it.

Also, a recent post on Nobu’s blog shows how to get rid of the center DC spike in SDRuno by adjusting the Channel Skew Calibration. The post is in Japanese, but the gist of it is that you just need to adjust the fine tuning DC offset slider in the Channel Skew Calibration settings. Nobu also points out that a handy shortcut to getting the ExtIO window to display is to simply press the ‘H’ key.

Setting up the RTL-SDR for use in SDRuno.
Setting up the RTL-SDR for use in SDRuno.

SDR4Everyone: Review of the HackRF

Over on his ‘SDR4Everyone’ blog author Akos has recently uploaded a new post that reviews the HackRF One, and also compares it against the SDRplay RSP and RTL-SDR. In his review he discusses his first impressions of the HackRF, his concerns about it being labelled as a transceiver, and some of its various features. He also does a screenshot comparison of the HackRF, RSP and RTL-SDR on shortwave reception and image rejection performance. Akos also notes that there are not many applications in the high gigahertz range that cannot be done with cheaper or more specialized equipment. Finally he concludes that the HackRF is not very sensitive or good at RX in general, but still has enough features to make it a worthwhile purchase for some people.

If you are interested in the HackRF, we also have our own review that compares the HackRF, SDRplay RSP and Airspy.

The SDRplay and HackRF One.
The SDRplay and HackRF One.

Sniffing ANT-FS with an RTL-SDR and MMDS Downconverter in Pothos

ANT-FS is a wireless file transfer protocol that is designed specifically for transferring files wireless between two devices. It is designed for ultra low power devices and typically runs on devices operated by a coin sized battery. It is commonly used in applications like fitness tracker devices, which store data to later be downloaded to a PC.

Over on YouTube user sghctoma has uploaded a video showing a teaser of him receiving and decoding ANT-FS packets with blocks developed for the POTHOS graphical language. As ANT-FS is usually transmitted at 2.4 GHz, he had to use a MMDS downconverter which allowed his RTL-SDR to receive the packets. Sghctoma writes that the video is simply a teaser, and that a live demo with real deivce, and the full code + details will be released during his talk at DEFCON titled “Help, I’ve got ANTs!!!”.

ANT-FS sniffing with RTL-SDR, an MMDS downconverter and Pothosware

Testing L-Band Inmarsat Reception with Three LNA4ALL’s + Two Filters

Over the last few weeks Adam 9A4QV has been testing L-Band Inmarsat reception with his LNA4ALL low noise amplifiers. In a previous post he tested reception with two LNA4ALL and found that he got an improved SNR ratio over using just one LNA4ALL. In his latest video he tests Inmarsat reception with three LNA4ALL’s and two L-band filters. His results show that the SNR is improved over using two LNA4ALL’s, and can almost match the results obtained by a commercial L-band front end which he also demonstrated in a previous video.

3x LNA4ALL on L-band + 2 Filters

Building a Quad RTL-SDR Receiver for Radio Astronomy

Amateur radio astronomer Peter W East has recently uploaded a new document to his website. The document details how he built a quad RTL-SDR based receiver for his radio astronomy experiments in interferometry and wide-band pulsar detection (pdf – NOTE: Link Removed. Please see his website for a direct link to the pdf “Quad RTL Receiver for Pulsar Detection”. High traffic from this post and elsewhere has made the document go offline several times). Interferometry is a technique which uses multiple smaller radio dishes spaced some distance apart to essentially get the same resolution a much larger dish. Pulsars are rapidly rotating neutron stars which emit radio waves, and the strongest ones can be observed by amateur radio telescopes and a receiver like the RTL-SDR.

The Quad receiver has four RTL-SDR’s all driven by a single TCXO, mounted inside an aluminum case with fans for air cooling. He also uses a 74HC04 hex inverter to act as a buffer for the 0.5 PPM TCXO that he uses. This ensures that the TCXO signal is strong enough to drive all four RTL-SDRs.

The Quad RTL-SDR with air cooling.
The Quad RTL-SDR with air cooling.

Whilst all the clocks are all synced to a single master clock, synchronisation between the RTL-SDR’s is still difficult to achieve because of jitter introduced by the operating system. To solve this he introduces a noise source and a switch. By switching the noise source on and off, correlation of the signal data can be achieved in post processing.

Noise Source and Switch Calibration Unit.
Noise Source and Switch Calibration Unit.
How correlation with the pulsed noise source works.
How correlation with the pulsed noise source works.

In the document Peter shows in detail how the system is constructed, and how it all works, as well as showing some interferometry results. The system uses custom software that he developed and this is all explained in the document as well.

Using the SUP-2400 Downconverter with an LNA and RTL-SDR to Receive 2.4 GHz Video

Earlier in June YouTube user T3CHNOTURK posted a video demonstrating him receiving signals above the maximum 1.7 GHz range of the RTL-SDR by using a modified SUP-2400 downconverter. Back in April it was discovered by KD0CQ that a $5 DirecTV SUP-2400 circuit could be modified and turned into a downconverter for use with the RTL-SDR.

Now T3CHNOTURK has uploaded a new video showing more demonstrations of the RTL-SDR + SUP-2400 combo in action. This time he adds a PGA-103 based LNA to boost the signal strength, which gives him better effective range. In the video he shows reception of a wireless keyboard once again, and then goes on to show him receiving 2.4 GHz analog PAL video using the RTL-SDR program TVSharp. The picture is not particularly clear, but it is a decent demonstration.

RTLSDR, TVsharp 2.4 Ghz video receiver moded SUP-2400 & pga-103 LNA

Remote Spectrum Monitoring Drone with OpenWebRX, Raspberry Pi and an RTL-SDR

Recently Zoltan of rfsparkling.com wrote in to us to show us how he combined efforts with András (programmer of the OpenWebRX software) to create a proof of concept remote spectrum monitoring drone. The drone uses an RTL-SDR connected to a Raspberry Pi, and the Raspberry Pi runs an OpenWebRX server which broadcasts the radio data via 4G mobile internet. The full connection flow chart goes as follows:

[Drone] Antenna –> RTL-SDR –> RPi 2 –> OpenWebRX Server –> 4G mobile net –> … Internet … [Notebook] –> 4G mobile net –> Browser with OpenWebRX client

Zoltan writes that some possible applications include emergency communications, ham radio, 3D spectrum mapping, etc. In the future he also hopes to add TX capabilities, so that the drone can also work a a makeshift transceiver tower. The biggest limitation that Zoltan noted is the flight time of only about 10 minutes. However, a solution he suggests for future experiments is using wire powered drones.

In previous posts we showed Hak5’s remote RTL-SDR ADS-B drone. Their results were not particularly great, however Zoltan and András’ results seem to be much better.

The video below shows an example of Zoltan and András’ drone experiments.

Remote Spectrum Analyzer Drone With OpenWebRX using RTL-SDR and Raspberry Pi