Category: Other

Demonstrating Two Channel Coherent Spatial Filtering In a GNU Radio Simulation

Over on YouTube VE6EY has uploaded a video that demonstrates spatial filtering (aka beamforming) working in a GNU Radio simulation. This is a technique that can be used with a 2-channel coherent SDR with to nullify local interference. One SDR is connected to an antenna for receiving the distant signal, and the second is connected to a noise probe that is designed to receive only the local noise source.

The demonstration is not performed with real SDRs, but with prerecorded signals, although it still shows the effectiveness of the technique. In the video VE6EY shows switch mode and powerline noise being nulled out from some AM music, and explains through a demo why phase coherence is required.

V36EY gives further information and a link to download the demo over on his blog post.

SDR Spatial Filtering Demo

A Review of the miniVNA Pro Vector Network Analyzer

Over on YouTube Kevin Loughin has reviewed the miniVNA Pro Vector Network Analyzer (VNA). A VNA is a tool that can be used to measure antenna or coax parameters such as SWR, impedance, loss as well as characterize filters. It is a very useful tool to have if you are building antennas, filters or RF circuits. The RTL-SDR with a noise source can somewhat be used as a network analyzer, but a fully functional VNA will be a lot more accurate and easier to use. The miniVNA costs US$490 and is significantly cheaper compared to desktop based VNAs.

In the video Kevin explains what a VNA is and that the miniVNA Pro is, shows how to calibrate the unit, shows some measurements on his roof mounted dipole, measures a home made filter, and then demonstrates portable operation of the device on an Android phone. The miniVNA Pro has a built in battery so it can be used portably in the field together with an Android phone and bluetooth.

We ourselves have the miniVNA tiny which operates in frequency from 1 MHz all the way up to 3 GHz, whereas the miniVNA Pro operates from 0.1 MHz to 200 MHz. However the tiny does not have portable operation. The miniVNA tiny is excellent for building things like ADS-B and Inmarsat antennas.

The miniVNA Pro and Tiny can both be found for sale on Ham Radio Outlet.

Ham Radio - A look at the miniVNA PRO Vector Network Analyzer

Reprogramming Vaisala RS-41 Radiosondes to Transmit APRS, RTTY, CW in the Ham or ISM Bands

Radiosondes are light weight sensor packages that are attached to weather balloons. They transmit live RF weather telemetry down to earth as they rise. With an RTL-SDR and appropriate antenna it can be possible to decode this telemetry. One related hobby that a few people enjoy is radiosonde chasing, which is tracking and collecting radiosondes once they have fallen back to the earth. Some people collect them as trophies, and others like to repurpose them. For example in this previous post we've seen how some radiosondes can be repurposed into L-band antennas for RTL-SDR's.

Another way to repurpose radiosondes has recently been submitted to us by regular contributor 'happysat' who wrote in and let us know that it is actually possible to reprogram the commonly used Vaisala RS-41 radiosondes into being able to transmit ham radio APRS, RTTY or CW mode signals in the ISM or ham bands. The initial hack was first performed by SQ5RWU, and then OM3BC who managed to create easier to use software that could reflash the radiosondes internal firmware via the serial port on the radiosonde. This hack could be useful for any ham requiring a cheap transmitter for their own high altitude balloon experiments.

Happysat ended up testing this software with some RS-41 radiosondes that he had, and managed to receive some generated signals with an RTL-SDR of his. Some photos that he's submitted are shown at the end of this post.

In addition to the above, happysat also wanted to mention his other radiosonde re-purposing project which was turning a DFM-06 and DFM-09 into a functional GPS unit that could be used for navigation when connected to a laptop, or to sync time on PCs.

Transmit APRS
PE2BZ's Modded RS41 with Solar Panels
RS41 Programmer
Transmit APRS PE2BZ's Modded RS41 with Solar Panels RS41 Programmer
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Demonstrating Two Channel Coherent Spatial Filtering In a GNU Radio Simulation

Over on YouTube VE6EY has uploaded a video that demonstrates spatial filtering (aka beamforming) working in a GNU Radio simulation. This is a technique that can be used with a 2-channel coherent SDR with to nullify local interference. One SDR is connected to an antenna for receiving the distant signal, and the second is connected to a noise probe that is designed to receive only the local noise source.

The demonstration is not performed with real SDRs, but with prerecorded signals, although it still shows the effectiveness of the technique. In the video VE6EY shows switch mode and powerline noise being nulled out from some AM music, and explains through a demo why phase coherence is required.

V36EY gives further information and a link to download the demo over on his blog post.

SDR Spatial Filtering Demo

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A Review of the miniVNA Pro Vector Network Analyzer

Over on YouTube Kevin Loughin has reviewed the miniVNA Pro Vector Network Analyzer (VNA). A VNA is a tool that can be used to measure antenna or coax parameters such as SWR, impedance, loss as well as characterize filters. It is a very useful tool to have if you are building antennas, filters or RF circuits. The RTL-SDR with a noise source can somewhat be used as a network analyzer, but a fully functional VNA will be a lot more accurate and easier to use. The miniVNA costs US$490 and is significantly cheaper compared to desktop based VNAs.

In the video Kevin explains what a VNA is and that the miniVNA Pro is, shows how to calibrate the unit, shows some measurements on his roof mounted dipole, measures a home made filter, and then demonstrates portable operation of the device on an Android phone. The miniVNA Pro has a built in battery so it can be used portably in the field together with an Android phone and bluetooth.

We ourselves have the miniVNA tiny which operates in frequency from 1 MHz all the way up to 3 GHz, whereas the miniVNA Pro operates from 0.1 MHz to 200 MHz. However the tiny does not have portable operation. The miniVNA tiny is excellent for building things like ADS-B and Inmarsat antennas.

The miniVNA Pro and Tiny can both be found for sale on Ham Radio Outlet.

Ham Radio - A look at the miniVNA PRO Vector Network Analyzer

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Reprogramming Vaisala RS-41 Radiosondes to Transmit APRS, RTTY, CW in the Ham or ISM Bands

Radiosondes are light weight sensor packages that are attached to weather balloons. They transmit live RF weather telemetry down to earth as they rise. With an RTL-SDR and appropriate antenna it can be possible to decode this telemetry. One related hobby that a few people enjoy is radiosonde chasing, which is tracking and collecting radiosondes once they have fallen back to the earth. Some people collect them as trophies, and others like to repurpose them. For example in this previous post we've seen how some radiosondes can be repurposed into L-band antennas for RTL-SDR's.

Another way to repurpose radiosondes has recently been submitted to us by regular contributor 'happysat' who wrote in and let us know that it is actually possible to reprogram the commonly used Vaisala RS-41 radiosondes into being able to transmit ham radio APRS, RTTY or CW mode signals in the ISM or ham bands. The initial hack was first performed by SQ5RWU, and then OM3BC who managed to create easier to use software that could reflash the radiosondes internal firmware via the serial port on the radiosonde. This hack could be useful for any ham requiring a cheap transmitter for their own high altitude balloon experiments.

Happysat ended up testing this software with some RS-41 radiosondes that he had, and managed to receive some generated signals with an RTL-SDR of his. Some photos that he's submitted are shown at the end of this post.

In addition to the above, happysat also wanted to mention his other radiosonde re-purposing project which was turning a DFM-06 and DFM-09 into a functional GPS unit that could be used for navigation when connected to a laptop, or to sync time on PCs.

Transmit APRS
PE2BZ's Modded RS41 with Solar Panels
RS41 Programmer
Transmit APRS PE2BZ's Modded RS41 with Solar Panels RS41 Programmer
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Another GUI for Outernet’s Wideband Signal Generator moRFeus

Thanks to Ohan Smit for submitting news of his newly released GUI for Outernet's moRFeus wideband signal generator. Ohan's GUI works in both Linux and Windows. The Windows release can be downloaded from the GitHub Releases page. With the GUI you can change the mode between Mixer/Generator, generate noise, run a sweep, turn the bias tee on/off and generate a CW message.

A few days ago we also posted about about a moRFeus GUI by "Lama Bleu" which has similar functions. Although it only appears to run in Linux, Lama Bleu's GUI can interface directly with GQRX.

moRFeus is still currently on sale at CrowdSupply for $149 for the next 19 hours from the time of this post. The price is expected to rise after.

moRFeus GUI Generating a Sweep
moRFeus GUI Generating a Sweep
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New GUI and Info on Outernet’s moRFeus Wideband Signal Generator

Back in March we posted about the release of Outernet's moRFeus device which is a low cost wideband RF signal generator. Since then we've received a few emails from two readers who've received their units and have found some interesting hacks and have developed software for it.

First we have a submission from Ohan Smit who discovered a hack that allows moRFeus to work as a wideband noise generator by setting the LO to 5 GHz and the Mixer current to 3. Together with an Airspy and the Spectrum Spy software he was able to measure the response of a bandstop FM filter. Over on the forums he also shows screenshots of Python based control software that he's developed for controlling moRFeus.

moRFeus Generating Noise
moRFeus Generating Noise

Next we have a moRFeus Linux GUI created by "Lama Bleu". It can be used to access the same functions as via the moRFeus LCD screen, but is also has a few very useful features such as a step generator which allows a generated tone to sweep across the frequency spectrum. The moRFeus GUI can also connect to GQRX and sync with the LO frequency specified in the GQRX GUI for easy control. It should also be possible to implement a CW morse code generator with some scripts.

Outernet moRFeus GUI
Outernet moRFeus GUI

Over on the forums Zoltan, one of moRFeus' designers also notes that it might even be possible to use moRFeus for WSPR modulation, although this isn't confirmed yet. It seems that moRFeus is shaping up to be a very useful tool for RF testing and experimentation.  The device is currently still available on Crowd Supply for $149US with over 136 units sold so far.

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Nexmon SDR: Using the WiFi Chip on a Raspberry Pi 3B+ as a TX Capable SDR

Back in March of this year we posted about Nexmon SDR which is code that you can use to turn a Broadcom BCM4339 802.11ac WiFi chip into a TX capable SDR that is capable of transmitting any arbitrary signal from IQ data within the 2.4 GHz and 5 GHz WiFi bands. In commercial devices the BCM4339 was most commonly found in the Nexus 5 smartphone.

Recently Nexmon have tweeted that their code now supports the BCM43455c0 which is the WiFi chip used in the recently released Raspberry Pi 3B+. They write that the previous Raspberry Pi 3B (non-plus) cannot be used with Nexmon as it only has 802.11n, but since the 3B+ has 802.11ac Nexmon is compatible. 

Combined with RPiTX which is a Raspberry Pi tool for transmitting arbitrary RF signals using a GPIO pin between 5 kHz to 1500 MHz, the Raspberry Pi 3B+ may end up becoming a versatile low cost TX SDR just on it's own.

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Nexmon SDR: Turning a Broadcom 802.11ac WiFi Chip into a TX Capable Software Defined Radio

Over on GitHub we've recently seen the release of some interesting code called "Nexmon Software Defined Radio" which demonstrates a discovery that allows a Broadcom 802.11ac WiFi chip to be used as a transmit capable software defined radio. This means that it can be used to transmit (within the 2.4 GHz and 5 GHz WiFi bands) any arbitrary signal from IQ data. The specific WiFi chip used in their experiments is the US$10 BCM4339 which has been found in smartphones such as the Nexus 5. It's not clear if other Broadcom 802.11ac WiFi chips could also work.

To begin with Nexmon SDR you'll need a development environment set up on a Nexus 5 smartphone. Then it's a matter of downloading the dependencies, installing the Android NDK, and compiling Nexmon. IQ data can then be transmitted in code using from special system commands.

The Nexmon team have indicated on Twitter that they plan to present a paper with more information on Nexmon SDR at the MobiSys 2018 conference which will be held in June.

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Building an IcoBoard FPGA based Software Defined Radio

The IcoBoard is an FPGA IO board that is compatible with the Raspberry Pi. An FPGA (Field Programmable Gate Array) is a silicon chip that can implement custom digital circuits (such as DSP processors) and be reconfigured with different circuits many times. Other silicon chips are ASICs (application specific integrated circuit) which have circuits that are set in stone.

Over on YouTube OpenTechLab has been trying to create a software defined radio with his IcoBoard FPGA. To do this he's combined it with an audio A2D/D2A (analog-to-digital/digital-to-analog) converter board and a Raspberry Pi. The video goes through the entire design process, including A2D/D2A selection and purchasing, PCB adapter design in KiCad, soldering the PCB, as well as 3D printing a frame.

In the last part of the video he does a simple test where a signal is input into the A2D converter, converted to digital and processed by the FPGA. The circuitry programmed into the FPGA then simply outputs the received data to the D2A which converts it back into an analog signal. In the next steps of the project OpenTechLab hopes to work on the software and turn it into a full SDR. Show notes for the video are available here.

[014] IcoBoard Software Defined Radio Project - Hardware

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