Thank you to Frugal Radio for submitting a YouTube video where he tests the YouLoop on an RTL-SDR Blog V3 running in direct sampling mode. The YouLoop is a passive HF loop antenna that requires a highly sensitive SDR like the Airspy HF+ Discovery to work at its full potential. However, in direct sampling mode the RTL-SDR Blog V3 does have enough sensitivity to work with the antenna to some extent thanks to the HF amplifier that is used on the direct sampling circuit. In the video Frugal Radio demonstrates the YouLoop receiving various HF signals.
Will an AirSpy YouLoop work with an RTL-SDR v3 on HF in direct sampling mode? It shouldn't...
We also note a second video by Bartłomiej Marcinkowski which shows an RTL-SDR Blog V3 in direct sampling mode running with a DIY YouLoop and MiniWhip. The MiniWhip does have increased signal strength, but the YouLoop is still usable and may be a better choice in the presence of interference. Later in the video he compares the RTL-SDR Blog V3 with MiniWhip against the Airspy HF+ Discovery with DIY YouLoop.
RTL-SDR v3 & YouLoop vs RTL-SDR v3 & MiniWhip vs AirSpy HF+ Discovery & YouLoop [80m,40m,20m]
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)
The designs include the PCB Gerber files for manufacturing, the components list and assembly and usage guides. Also both through-hole and SMD designs are provided.
The Mini-Whip design has a frequency range of 10 kHz - 30 MHz and to power it you'll need a 5 - 13V bias tee. You will need to install it up high and preferably away from the house as Mini-Whips are quite susceptible to local noise pickup. Another very important point is that Mini-Whips need to have a good ground connection. The upconverter is based on the ADE-1 mixer, and uses a 125 MHz local oscillator.
Igor's documentation on the project is excellent, and is a good read for getting more information about upconverters and Mini-Whips. He has noted that he is sending us some samples of units that he's built, so when we receive them we'll post again with test results. It looks as if he's put a lot of research into these designs so we're looking forward to seeing how well they work.