Back in June we posted about DE8MSH’s rtl_power based heatmap viewer which was automatically generated every day from a Raspberry Pi. The browser based heatmap display provides a way to view the frequency and time of where the mouse pointer is allowing you to easily identify signals.
Back then the code was unavailable but now DE8MSH has released his code on GitHub. An example heatmap generated by the code can be found here.
Amateur radio hobbyist DE8MSH recently wrote in to let us know about a project he has been working on. His project involves using a Raspberry Pi B and RTL-SDR to automatically log a wide band heatmap using rtl_power. Rtl_power is a command line tool that will log signal strengths to a csv file using the RTL-SDR over a very large definable bandwidth.
To do the automatic logging the Raspberry Pi runs rtl_power for 23 hours constantly writing data to a mounted hard drive. After 23 hours the heatmap image is calculated and then uploaded to a webpage at http://qth.at/de8msh/
DE8MSH has also been working on a second related project over at http://www.qth.at/de8msh/hm/pic.html. The heatmap on this page shows various transmissions from weather balloons. As you mouse over those transmissions, the QTH (location) of those weather balloon transmissions is shown as well as the frequency and time of where the mouse pointer currently is.
Over on his blog, OZ9AEC has uploaded a post showing how he was able to create a live HDTV transmitter out of a Raspberry Pi, a Raspi Cam module and a UTC DVB-T Modulator adaptor. As he does not want to interfere with commercial DVB-T broadcasts, he sets the module to transmit at 1.28 GHz, aka the 23 cm licenced ham radio band.
On the RTL2832U dongle side, he modified the RTL2832U Linux DVB-T drivers (not the SDR drivers) to work on the 1.3 GHz band. The intention of this camera is for it to fly on a rocket mission. In the YouTube video below he has uploaded some sample footage with the RTL2832U dongle receiving the stream from 300 meters away.
Over on YouTube user SilverXiaify has uploaded a video of a project he completed for a class in his electrical engineering school. His project involves controlling a remote controlled car using a ham radio. The remote control car carries on board an RTL-SDR for signal reception and an Raspberry Pi for data processing and control. The communications protocol they used is a naive version of AFSK700.
In November last year we posted a story showing how a Raspberry Pi could be used to transmit a digital AFSK signal to an RTL-SDR or other radio simply by connecting a wire to a GPIO pin.
Now an rtl-sdr.com reader has written in to let us know that this concept has also been used before to create a 1 – 250 MHz FM transmitter using the Raspberry Pi and a program called PiFM. It uses the same concept of connecting a wire antenna to one of the GPIO pins but modulates the frequency using hardware on the Rpi meant to generate spread spectrum clock signals. It is claimed that it can transmit up to 50m away.
Below we show an example YouTube video of the Raspberry Pi FM radio transmitting to an RTL-SDR running HDSDR.
Over on our Facebook page Micheal Kent has posted about his raspberry pi based RTL-SDR receiver which runs rtl_udp. There’s not much more information on this project, but the video he posted shows what appears to be a Raspberry Pi and RTL-SDR dongle mounted inside an icecream box. There are two knobs mounted on the outside that control the brightness of an LCD screen which shows the tuned frequency, and another knob which controls the frequency itself.
Hackaday brings to attention a simple hack where hacker Marc uses an antenna connected to a general purpose I/O (GPIO) pin on his Raspberry Pi to wirelessly transmit a wav file via AFSK modulation to his RTL-SDR. He uses a program called minimodem to encode the wav on the Raspberry Pi and then on the PC to decode the data received by the RTL-SDR.
Using this method, it is claimed that a signal can be transmitted up to 50m away, even through walls.
Over on YouTube user adsbrus shows us his project which is an in car ADS-B aircraft tracker using a Raspberry Pi mini computer and an RTL-SDR. The system uses an LCD screen mounted where the car radio usually is to show aircraft identifier, altitude, and speed information in text.
