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)
Over on YouTube user [Radio Electronics] has uploaded a useful video showing how to install your own personal SDRplay or RTL-SDR based WebSDR for QO-100 (aka Es'Hail-2) reception. Es'Hail-2 is the first geostationary satellite with amateur radio transponders on board, and is positioned at 25.5°E which covers Africa, Europe, the Middle East, India, eastern Brazil and the west half of Russia/Asia.
The idea behind a WebSDR is to run your RTL-SDR QO-100 receiver on a remote Raspberry Pi (perhaps mounted close to the antenna on your roof etc). The Pi runs custom WebSDR software that has been created from scratch by [Radio Electronics] specifically for monitoring Es'Hail-2. Then you can access your QO-100 receiver from any device on your network that has a web browser (computer/phone/tablet etc). The interface of his WebSDR appears to be quite slick, which multiple QO-100 specific options and labels.
Quite a lot of work must have gone into this software which looks to be of high quality, so it is definitely worth checking out if you are interested in QO-100/Es'Hail-2 monitoring.
In the first video he first talks about various methods for downconverting the 10489.550 MHz QO-100 CW signal into a range receivable by the RTL-SDR or SDRplay. He then goes on to show the exact steps to install and run his WebSDR software on a Raspberry Pi 3.
In the second video he goes on to demonstrate the web browser interface highlighting the QO-100 specific features that he has implemented such as being able to compensate for any LNB frequency drift via a feature that can lock to the QO-100 PSK beacon.
SDRPlay have recently published a video demonstrating how the new RSPduo diversity feature in SDRUno can be used to cancel local interference. 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 should allow for interesting phase coherent applications such as diversity. The RSPDuo's diversity feature allows us to either combine two antenna signals together for an up to 3 dB increase, or for removal of an unwanted noise source via subtraction of signals.
In the video they show a broadcast AM signal that has it's SNR reduced by being on top of a local electrical noise source. The use a Bonito Mega-dipole on tuner 1, and a Bonito Mini-whip on tuner 2. The Mini-whip appears to receive the local interference stronger, so can be subtracted away from the Mega-dipole's signal with the diversity function. The result is improved SNR, and the noise is almost entirely cancelled.
There are 2 very practical applications for diversity software. The first is MRC (Maximum Ratio Combination) Diversity which, in order to be effective, needs two antennas presenting the same signal with some degree of diversity. Then there is this second impressive application which is becoming more and more useful due to the growing number of domestic sources of interference.
This is possible in an RSPduo, due to the coherent nature of the combined tuner streams being presented to the computer for processing.
Using Diversity in SDRplay's SDRuno to Cancel Local Interference
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 should allow for interesting phase coherent applications such as diversity.
From V1.32 onwards, MRC (Maximal Ratio Combining) Diversity is supported using the RSPduo. MRC Diversity can be used to combine the 2 tuner input streams together to potentially improved the SNR (signal to noise ratio). The same frequency is used for both tuners in the RSPduo and the gain can be adjusted either on each tuner independently or locked together (the default method).
Diversity mode is enabled by clicking on the RSPduo MODE dropdown and select DIVERSITY. Make sure both the 50 ohm ports are connected to the correct input source and note that the HiZ port is not available for Diversity mode. Trying to use the HiZ port will result in an error message being displayed.
Over on his YouTube channel SignalsEverywhere, Corrosive has just released a new video titled "Software Defined Radio Introduction | What SDR To Buy? | Choose the Right one For You". The video is an introduction to low cost software defined radios and could be useful if you're wondering which SDR you should purchase.
The video includes a brief overview of the Airspy, KerberosSDR, PlutoSDR, LimeSDR Mini, HackRF, SDRplay RSPduo and various RTL-SDR dongles. In addition to the hardware itself Corrosive also discusses the compatible software available for each SDR.
Software Defined Radio Introduction | What SDR To Buy? | Choose the Right one For You
At this years Hamvention Chris Howard from ICQ Amateur interviewed Andy at the SDRplay booth. In the interview they discuss various new features and improvements to SDRuno, the official software for SDRplay devices.
Later they also discuss the RSPduo, and the new diversity feature coming in a new version of SDRUno that is due to be released in a few weeks. The diversity feature works with the two tuners on the RSPduo to combine or subtract signals from two different antennas. Andy notes that diversity should be able to achieve a net 3dB increase in SNR, and is most useful for a moving or dynamic signal environment.
Finally Andy discusses the future development of SDRUno and notes that they're working on a plugin environment which will allow the creation of third party demod/decoders, a multiplatform server for remote SDR, and eventually cross platform drivers and SDRUno.
SDRPlay Announce Update to SDRUno and Future Plans for Software Defined Radio at Hamvention 2019
Steve Andrew, the author of the SDRplay Spectrum Analyzer software has recently released an update which enables several new features. This software allows you to use SDRplay SDRs to scan a wide swath of bandwidth by rapidly scanning in 10 MHz (or less) chunks over the SDRplay's frequency range. The SDRplay team write:
We are pleased to announce the availability of V1.0a of the Spectrum Analyser software developed by Steve Andrew specifically for the RSP line of products. This is a very-much upgraded version of the original alpha release and includes many new features as well as removing the limitations imposed on the previous version. New features include multiple traces, a versatile marker system with maths, peak find and display functions, Zero or non-Zero IF options and an upgraded tracking generator system. Currently support are:
Over on YouTube user ElPaso TubeAmps has uploaded a video showing his transit/receiver relay system that allows a "boat anchor" (old radio) ham radio transmitter and SDRplay SDR receiver to coexist. In order to protect the SDRplay's front end from being destroyed by a ham radio transmitting on the same antenna, a relay should be used to ground the SDRplay during a ham radio transmission. He writes:
How to build a small chassis and relay system to switch the antenna from the SDR input to ground and open the speaker connection from the PC to the speakers during transmit. I use "boat anchor", i.e. separate VFO for transmitter and receiver equipment and this video is about that type of connection and is not for transceivers.
SDRPlay, RTL-SDR, Transmit-Receive , PC Speaker, T/R Switch