SDRplay RSPDuo Diversity: Combing a Magnetic Loop and Miniwhip Antenna

The SDRplay team have posted some more videos that demonstrate the SDRplay Duo's diversity function. The SDRplay RSPDuo is a 14-bit dual tuner software defined radio capable of tuning between 1 kHz - 2 GHz. It's defining feature is that it has two receivers in one radio, which allows us to combine the signal from two antenna together.

In the video Jon uses a Wellbrook Magnetic Loop antenna and a Bonito Miniwhip antenna both connected to the RSP Duo. Individually each antenna receives the signal relatively poorly and fades in and out as conditions and signal reflections fluctuate. However, with diversity enabled the SNR is improved and fading is significantly reduced.

The method they use to combine signals is a relatively simple method called maximum-ratio combining (MRC). The idea is that the two signal channels are added together, with the currently stronger and less noisy channel having increased gain. So while the signal levels fluctuate, as long as one antenna can receive the signal you will see no fading.

SDRplay HF Diversity Demo

SDRplay note that the key to a good setup is to have the antennas spaced out at a quarter wavelength of the signal frequency that you are receiving. In a second video they show how to properly set up an antenna system for proper HF diversity receiving.

This video demonstrates how SDRuno diversity and the RSPduo can bring enhanced reception at HF using 2 antennas separated by approximately a quarter wavelength. It uses the the current version of SDRuno (V 1.32) and the dual tuner RSPduo SDR from SDRplay.

In this experiment we had a wire dipole with one leg approximately a quarter wavelength from a Boniwhip vertical - both were picking up similar strength signals before going into "diversity" (max ratio combination) mode.

The benefits of diversity tuning at HF are very dependent on many variables, most notably the changing nature of the reflected signal path and the degree to which noise and unwanted signals are not as coherent as the wanted signal.

Antenna and SDRplay set-up for HF diversity reception (rev1)

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Using an Airspy HF+ Discovery to Hunt for HF Beacons

Over on YouTube Tech Minds has posted a video of him using an Airspy HF+ Discovery to hunt for signals like non-direction beacons (NDB's) and other morse code CW beacons. The Airspy HF+ Discovery is a new software defined radio that builds upon the already excellent original Airspy HF+.

One key improvement that many people have been experimenting with is it's improved VLF and LF capabilities, which is where most beacons are. It is capable of tuning down to 0.5 kHz (500 Hz). Over on Twitter, @prog (creator of these Airspy products) has been experimenting with simple and small ferrite loop antennas for VLF/LF and finding excellent results due to the low noise figure and good impedance matching of the HF+ Discovery.

Hunting LF/MF/HF Beacons With An Airspy HF+ Discovery

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Reviews of the NanoVNA: An Ultra Low Cost $50 Vector Network Analyzer

A vector network analyzer (VNA) is an instrument that can be used to measure antenna or coax parameters such as SWR, impedance and loss. It can also be used to characterize and tune filters. It is a very useful tool to have if you are building and tuning home made antennas, filters or other RF circuits. For example if you are building a QFH or ADS-B antenna to use with an RTL-SDR, a VNA can help ensure that your antenna is properly tuned to the correct frequency. Compared to a standard SWR or network analyzer a VNA supplies you with phase information as well.

Until just recently, VNA's have cost roughly US$500 for a decent USB PC based unit like the miniVNA or PocketVNA, and have set people back thousands to tens of thousands of dollars for bench top units.

However, the cost of owning a VNA has now been reduced to only US$50 thanks to the NanoVNA. The open source NanoVNA project by @edy555 and ttrftech has been around since 2016, but only recently have Chinese sellers begun mass producing the unit and selling them on sites like Aliexpress, eBay and now Amazon. We note that it seems that there are some sellers selling them without shielding, so it might be worth double checking the listing to see if they mention that. All the listings we've seen seem to come with simple calibration kits as well.

The NanoVNA: A $50 Vector Network Analyzer
The NanoVNA: A $50 Vector Network Analyzer

The NanoVNA is a small credit card sized VNA. It has a built in LCD screen that can be used to display graphs directly, or it can also be connected to a PC and the graphs viewed via the NanoVNA Windows software. When purchasing you can opt to include a small battery for portable operation for a few dollars extra. The frequency range is from 50 kHz to 900 MHz, although you should note that above 300 MHz dynamic range performance is reduced.

Over on YouTube several hams and radio enthusiasts have recently uploaded videos demonstrating and reviewing the NanoVNA. The overall consensus is that the unit is accurate and works well. For additional support there is forum available at Groups.IO.

Below YouTube user IMSAI Guy reviews the NanoVNA. Check out IMSAI Guy's other videos too as he has several where he tests the NanoVNA on difference filters and antennas, and checks the accuracy.

#350 NanoVNA Vector Network analyzer 900MHz VNA for $50

Below is YouTube user joe smith's review. He also has two other NanoVNA videos on his channel where he shows how to use the NanoVNA to measure antenna impedance, and how to use the NanoVNA to create SPICE models for simulation.

The NanoVNA, a beginners guide to the Vector Network Analyzer

Finally YouTube user Oli gives another overview. Please note that the following video is in Polish, but YouTube captions can be set to English.

NanoVNA - omówienie, kalibracja, pomiar anteny i filtra [english subtitles]

We've also seen several recent text reviews:

NanoVNA - A short review. In this review nuclearrambo shows off the calibration kit, and shows a practical measurements of a directional coupler and 137 MHz QFH antenna.

NanoVNA compared with a Keysight fieldfox N9952A. Here nuclearrambo provides a comparison between the $50 NanoVNA and the $40,000+ Keysight FieldFox N9962A.

The NanoVNA, a real VNA at less than 48 €!. A review written in French, but Google Translate can be used. In this review David Alloza compares the NanoVNA against an Agilent E5062A benchtop VNA, and results look comparable.

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WebWSPR: A Browser Based WSPR Decoder and Visualization Tool

A few days ago we posted about [dj0abr / Radio Electronics'] WebSDR software for QO-100. Having looked through his GitHub we've seen that he also has an a similar browser based server tool called WebWSPR for WSPR decoding and visualization (click with WebWSPR link) which was released earlier this year.

WSPR is an amateur radio digital HF mode designed to be decodable even if the signal is transmitted with very low power and is very weak. It can be used to help determine HF radio propagation conditions as WSPR reception reports are typically automatically uploaded to wsprnet. In the past we have been able to receive WSPR and similar modes like FT8 with our RTL-SDR V3 running in direct sampling mode.

Like his QO-100 WebSDR software, WebWSPR is designed to run on a single board computer like a Raspberry Pi or any Linux machine. It serves a web page that shows the WSPR waterfall, decoded data and has various WSPR related control options. The web page can be accessed remotely from any machine on the same network as the server, or could be put on the internet with port forwarding and a hostname service like noip.

A ready to use Raspberry Pi image for WebWSPR is available here (does not seem to support the latest Pi4 or 3B+ however). Manual installation instructions can be found here. The code is all open source and available on GitHub.

The software appears to take input from the soundcard for standard hardware receivers, but it should be possible to pipe audio from an RTL-SDR into pulseaudio, which the software can then use. The instructions from our RTL-SDR V3 WSJT-X tutorial may help.

WebWSPR Browser Screenshot
WebWSPR Browser Screenshot
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Hackaday Article about the Slow Death of NOAA-15

If you've been following our blog, or have your own RTL-SDR based weather satellite station, then you'll know that the NOAA-15 APT satellite has been experiencing issues lately. There appear to be problems with it's camera scan motor resulting from it running low on lubrication. This is fully understandable as the satellite is 21 years old and well past it's expected life span. The satellite appears to be working some days, and producing garbage image other days.

Over on Hackaday, Dan Maloney has uploaded an interesting article that explores the history and technology behind NOAA-15's camera, and why it is now failing.

When NOAA-15 fails for good, don't feel too bad as we still have NOAA-18 and NOAA-19, the Russian Meteor M2, and Meteor M2-2 satellites, and the GOES satellites, all of which can be received by an RTL-SDR. Several new weather satellites are also planned for 2020 and onwards.

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Talks from GNU Radio Days 2019

GNU Radio Days 2019 was a workshop held back in June. Within the last week recordings of the talks have been uploaded to YouTube by the Software Defined Radio Academy channel. The talks cover a wide range of cutting edge SDR research topics and projects. Many of the presenters have also made use of RTL-SDR dongles, as well as other higher end SDRs in their research.

All the talks are combined into two 3 hour long videos from the morning and day sessions from day one. Day two also has two videos that consist of recordings from the tutorial sessions which make use of the PlutoSDR. Finally there is also the keynote speech from Marcus Müller where he dives into the internal workings of GNU Radio.

Below we list the talks with timestamps for the YouTube video. Short text abstracts for each of the talks can also be found in the conference book. We note that not all the abstracts appear to have been presented in the videos, so it may be worth checking out the book for missed talks about passive radar, a 60 GHz link, embedded GNU Radio on a PlutoSDR, an SDR 802.11 infrared transmission system, PHY-MAC layer prototyping in dense IoT networks and hacking the DSMx Drone RC protocol.

Continue reading →

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Building a DIY 2.4 GHz Helical Feed for the QO-100/Es’Hail-2 Satellite

Over on his YouTube channel Adam 9A4QV has uploaded a short video that demonstrates his 2.4 GHz homemade helical feed designed to be used with a reflector (prime feed satellite dish) for QO-100/Es'Hail-2 satellite reception. The antenna is made from an old can, 2-turns of copper wire, and a plastic insulator to hold the turns in place. The two turns are wound in left hand circular polarization (LHCP), because when used with a satellite dish reflector it will result in right hand circular polarization (RHCP), which is the polarization QO-100 uses.

One of the most important parts of the video is when Adam shows how he matches the antenna to 50 Ohms. He notes that without matching the antenna won't work properly, and the return loss will be about 8 dB or even less, resulting in poor performance. With matching he obtains 30 dB return loss.

Helical feed for the 2.4 GHz QO-100 satellite

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Android ADS-B Flight Tracker with 3D Aircraft Display

ADSB Flight Tracker is an Android App that allows you to display ADS-B flight data in either 2D or 3D. It works either with data shared from others over the internet via aggregation sites like adsbexchange.com, or via your own home ADS-B receiver data coming from an RTL-SDR and dump1090 server on your home network. You can also directly connect to an RTL-SDR that is running on your phone and this will allow you to get data faster with less lag. Using data shared by others from the internet could have a delay of a few seconds.

In order to keep using the 3D and RTL-SDR features you'll need to unlock them for a small in-app purchase of $2 for each feature. Initially you get about 30 minutes trial time however.

2D and 3D Screenshots from ADS-B Flight Tracker
2D and 3D Screenshots from ADS-B Flight Tracker

Some interesting 3D videos were also recently posted to the apps Twitter page @ADSBFlightTrkr. 

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