Thank to LamaBleu for submitting news about his new software for the moRFeus signal generator and frequency mixer called moRFeus_listener. The software allows you to remotely control a moRFeus device via Telnet, TCP/UDP or HTTP. This could be used to control the moRFeus in a similar way to the short script that we used for generating a tracking tone in our previous tutorial on using measuring filters and antenna VSWR with the moRFeus.
LamaBleu also shared his results with using the harmonics of the moRFeus to generate a signal well past it's upper frequency limit of 5.4 GHz. He writes that by using the third harmonic is was able to generate a CW signal at 10.8 GHz and that tones up to harmonic 11 seem to work well.
As Outernet is currently having a sale and selling their their moRFeus product at only US $99 (see next post for details - or simply use coupon code "rtlsdrblog" on their checkout - valid until Saturday 09 May 18), we thought that we'd show an interesting use for the moRFeus when combined with an RTL-SDR.
Outernet's moRFeus is a signal generator and frequency mixer that can be controlled either by it's built in LCD screen, or via software on a Windows or Linux PC. It can generate a clean low phase noise tone anywhere between 85 to 5400 MHz. Because it can be computer controlled it is possible to use moRFeus as a tracking generator for characterizing filters and measuring antenna SWR. A tracking generator is just a signal generator that can be set to output at the same frequency that the measurement receiver is tuned to.
In the past we've posted a tutorial showing how to use a wideband noise source for measuring filters and antenna SWR. However, if available, a tracking generator is usually preferred over a noise source. A wideband noise source outputs high power at all frequencies, and so can easily overload an RTL-SDR causing reduced dynamic range and accuracy in measurements. This is especially the case when measuring bandstop filters as they pass all frequencies, apart from a small blocking band. Since so much noise gets through to the dongle, dynamic range is reduced.
This post shows how to use the moRFeus as a tracking generator together with an RTL-SDR for making RF measurements. This could be called a scalar network analyzer. The set up uses GQRX and a Python script, but in the future it is possible that someone may develop a standalone app.
Since the output of the moRFeus is quite strong, an attenuator is required to keep signal levels low enough to not overload the RTL-SDR.
The cheapest RF bridge we've found is available on eBay for about $7. With an RF Bridge you'll need a 50 Ohm dummy load as well to connect to the 'REF' port. Directional couplers seem to work more accurately however, and second hand minicircuits ones can often be found on eBay. A $2 TV 'tap' is also a directional coupler, and may also work, although we have not tested this.
Software Setup
In this tutorial we're using the method first described by 'LamaBleu' in his post to the Outernet forums. The method uses Linux and involves reading power levels from the RTL-SDR by using GQRX and it's remote telnet connection capabilities. The telnet command "F freq" can be used to change frequency in GQRX, and the command "l" can be used to read out the current power level in dbFS.
To control moRFeus we use Outernet's official "morfeus_tool", which is a command line based tool.
A basic Python script was written to set the frequency in moRFeus and GQRX at the same time. After a 500 ms settling time the power level is measured and recorded in a CSV file, then the script iterates to the next frequency. We iterate at 1 MHz intervals.
If you have a moRFeus and want to try this project out, copy and paste the script from pastebin, and name the file morfeus_scalar.py. Place the morfeus_scalar.py file and the morfeus_tool_linux_x32 tool into the home folder.
To get the software started:
Open GQRX and connect the dongle and required RF components for the test (shown below).
Set the RTL-SDR gain to zero or just low enough so that the signal doesn't cause overload (moRFeus signal levels are fairly high).
In the GQRX GUI ensure that the "Remote control via TCP" button is pressed in. (Looks like two computer screens).
Edit the Python script and choose the frequency range that you'd like to scan by setting variable FREQ_MIN and FREQ_MAX.
In a terminal run "sudo python morfeus_scalar.py".
When the script completes you'll have a file "out.txt" which is a CSV file of frequency and signal power levels.
Characterizing Filters
To characterize a filter (find the response of a filter) simply connect the system like so:
moRFeus Filter Test
But first connect just the moRFeus, attenuator and RTL-SDR together.
In GQRX increase the gain until just a few dB before the RTL-SDR overloads and starts showing signal images. This will maximize the available dynamic range.
Run an initial calibration scan with morfeus_scalar.py. Save the results in out.txt into a spreadsheet.
Connect the filter in the RF chain, and then run a second scan with morfeus_scalar.py. Save the results into another column in the spreadsheet.
Subtract the calibration scan results from the filtered results. Plot the resulting values using the spreadsheet software. This will show the response of the filter.
The PantronX Titus II is a yet-to-be-released portable Android tablet based SDR that we've been following since 2016. The device will feature a 100 kHz - 2 GHz tuning range, and software that focuses on HF digital DRM decoding, as well as DAB on VHF.
As you might be aware, we have joined up with Fraunhofer to include their MMPlayer app standard on Titus–what a difference a professional decoder, for both analog, DRM(+), and DAB(+), makes! MMPlayer is full featured even including reliable one way file downloads with DRM.
We are attempting also to license HD to include on the app for North America, making a truly worldwide receiver. Some deficiencies in our version of Android have caused issues as well as MMPlayer. All of which have caused delays leading to some serious business decisions – as you can imagine. You are correct that broadcasters have made large orders that will be fulfilled first. There are units in the field testing and such and continuing resolution of the software issues.
One of the issues that folks seem to have a hard time understanding is that we can not just build a few hundred or even thousands of units. Our minimum run is 10,000pcs! To do that everything has to be 100% – including the software. We simply will not ship units that are not 100%. Titus works, MMPlayer works – its that last 5% that takes the most time to resolve. These facts preclude any incremental production attempts. All that being said, we are very hopeful that the first production run is ready by last quarter of this year.
The AD9361 is a highly versatile full transceiver SDR chip released by Analog Devices back in 2013. With a frequency range from 70 MHz - 6 GHz, 56 MHz bandwidth and 12-bit ADC, it is most commonly found in high end SDRs such as the USRP range and PicoZed. On Digikey purchasing the chip today would set you back about USD $280. A cheaper but similar AD9363 chip is found in the PlutoSDR.
At the end of the post the author does a brief cost analysis on the chip, determining that while the total manufacturing cost of the chip is estimated at less than $5, the cost of R&D and IP per chip is about $33, and additional costs make up another $32 per chip. Profit between distributors and Analog Devices is about even, which each party taking about $100 per chip each.
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.
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
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.
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.
Thank to LamaBleu for submitting news about his new software for the moRFeus signal generator and frequency mixer called moRFeus_listener. The software allows you to remotely control a moRFeus device via Telnet, TCP/UDP or HTTP. This could be used to control the moRFeus in a similar way to the short script that we used for generating a tracking tone in our previous tutorial on using measuring filters and antenna VSWR with the moRFeus.
LamaBleu also shared his results with using the harmonics of the moRFeus to generate a signal well past it's upper frequency limit of 5.4 GHz. He writes that by using the third harmonic is was able to generate a CW signal at 10.8 GHz and that tones up to harmonic 11 seem to work well.
As Outernet is currently having a sale and selling their their moRFeus product at only US $99 (see next post for details - or simply use coupon code "rtlsdrblog" on their checkout - valid until Saturday 09 May 18), we thought that we'd show an interesting use for the moRFeus when combined with an RTL-SDR.
Outernet's moRFeus is a signal generator and frequency mixer that can be controlled either by it's built in LCD screen, or via software on a Windows or Linux PC. It can generate a clean low phase noise tone anywhere between 85 to 5400 MHz. Because it can be computer controlled it is possible to use moRFeus as a tracking generator for characterizing filters and measuring antenna SWR. A tracking generator is just a signal generator that can be set to output at the same frequency that the measurement receiver is tuned to.
In the past we've posted a tutorial showing how to use a wideband noise source for measuring filters and antenna SWR. However, if available, a tracking generator is usually preferred over a noise source. A wideband noise source outputs high power at all frequencies, and so can easily overload an RTL-SDR causing reduced dynamic range and accuracy in measurements. This is especially the case when measuring bandstop filters as they pass all frequencies, apart from a small blocking band. Since so much noise gets through to the dongle, dynamic range is reduced.
This post shows how to use the moRFeus as a tracking generator together with an RTL-SDR for making RF measurements. This could be called a scalar network analyzer. The set up uses GQRX and a Python script, but in the future it is possible that someone may develop a standalone app.
Since the output of the moRFeus is quite strong, an attenuator is required to keep signal levels low enough to not overload the RTL-SDR.
The cheapest RF bridge we've found is available on eBay for about $7. With an RF Bridge you'll need a 50 Ohm dummy load as well to connect to the 'REF' port. Directional couplers seem to work more accurately however, and second hand minicircuits ones can often be found on eBay. A $2 TV 'tap' is also a directional coupler, and may also work, although we have not tested this.
Software Setup
In this tutorial we're using the method first described by 'LamaBleu' in his post to the Outernet forums. The method uses Linux and involves reading power levels from the RTL-SDR by using GQRX and it's remote telnet connection capabilities. The telnet command "F freq" can be used to change frequency in GQRX, and the command "l" can be used to read out the current power level in dbFS.
To control moRFeus we use Outernet's official "morfeus_tool", which is a command line based tool.
A basic Python script was written to set the frequency in moRFeus and GQRX at the same time. After a 500 ms settling time the power level is measured and recorded in a CSV file, then the script iterates to the next frequency. We iterate at 1 MHz intervals.
If you have a moRFeus and want to try this project out, copy and paste the script from pastebin, and name the file morfeus_scalar.py. Place the morfeus_scalar.py file and the morfeus_tool_linux_x32 tool into the home folder.
To get the software started:
Open GQRX and connect the dongle and required RF components for the test (shown below).
Set the RTL-SDR gain to zero or just low enough so that the signal doesn't cause overload (moRFeus signal levels are fairly high).
In the GQRX GUI ensure that the "Remote control via TCP" button is pressed in. (Looks like two computer screens).
Edit the Python script and choose the frequency range that you'd like to scan by setting variable FREQ_MIN and FREQ_MAX.
In a terminal run "sudo python morfeus_scalar.py".
When the script completes you'll have a file "out.txt" which is a CSV file of frequency and signal power levels.
Characterizing Filters
To characterize a filter (find the response of a filter) simply connect the system like so:
moRFeus Filter Test
But first connect just the moRFeus, attenuator and RTL-SDR together.
In GQRX increase the gain until just a few dB before the RTL-SDR overloads and starts showing signal images. This will maximize the available dynamic range.
Run an initial calibration scan with morfeus_scalar.py. Save the results in out.txt into a spreadsheet.
Connect the filter in the RF chain, and then run a second scan with morfeus_scalar.py. Save the results into another column in the spreadsheet.
Subtract the calibration scan results from the filtered results. Plot the resulting values using the spreadsheet software. This will show the response of the filter.
The PantronX Titus II is a yet-to-be-released portable Android tablet based SDR that we've been following since 2016. The device will feature a 100 kHz - 2 GHz tuning range, and software that focuses on HF digital DRM decoding, as well as DAB on VHF.
As you might be aware, we have joined up with Fraunhofer to include their MMPlayer app standard on Titus–what a difference a professional decoder, for both analog, DRM(+), and DAB(+), makes! MMPlayer is full featured even including reliable one way file downloads with DRM.
We are attempting also to license HD to include on the app for North America, making a truly worldwide receiver. Some deficiencies in our version of Android have caused issues as well as MMPlayer. All of which have caused delays leading to some serious business decisions – as you can imagine. You are correct that broadcasters have made large orders that will be fulfilled first. There are units in the field testing and such and continuing resolution of the software issues.
One of the issues that folks seem to have a hard time understanding is that we can not just build a few hundred or even thousands of units. Our minimum run is 10,000pcs! To do that everything has to be 100% – including the software. We simply will not ship units that are not 100%. Titus works, MMPlayer works – its that last 5% that takes the most time to resolve. These facts preclude any incremental production attempts. All that being said, we are very hopeful that the first production run is ready by last quarter of this year.
The AD9361 is a highly versatile full transceiver SDR chip released by Analog Devices back in 2013. With a frequency range from 70 MHz - 6 GHz, 56 MHz bandwidth and 12-bit ADC, it is most commonly found in high end SDRs such as the USRP range and PicoZed. On Digikey purchasing the chip today would set you back about USD $280. A cheaper but similar AD9363 chip is found in the PlutoSDR.
At the end of the post the author does a brief cost analysis on the chip, determining that while the total manufacturing cost of the chip is estimated at less than $5, the cost of R&D and IP per chip is about $33, and additional costs make up another $32 per chip. Profit between distributors and Analog Devices is about even, which each party taking about $100 per chip each.
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.
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
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.
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.
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.
