More about diversity reception and the RSPduo

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jon
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Joined: Tue Jan 06, 2015 10:48 am

More about diversity reception and the RSPduo

Post by jon » Wed Jul 17, 2019 7:26 pm

It’s early days yet, for the new SDRuno diversity software which we recently launched with V1.32 for use with the dual tuner SDRplay RSPduo.
We are working on some video guides and more information on how it works.

Meanwhile we’d like to point out that there are 2 very practical applications for this 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. Examples of diversity are:

Spatial Diversity:
Using two antennas that are physically separated from one another. Depending upon the expected incidence of the incoming signal, sometimes a space on the order of a wavelength is sufficient. Other times much larger distances are needed – this can be challenging for HF frequencies and below.

Pattern Diversity: Using co-located antennas with different radiation patterns. This type of diversity makes use of directional antennas that are usually physically separated by some (often short) distance. Collectively they are capable of discriminating a large portion of angle space and can provide a higher gain versus a single omnidirectional radiator.

Polarization Diversity:
Combining a pair of antennas with orthogonal polarisations. Reflected signals can undergo polarization changes depending on the medium through which they are traveling. A polarization difference of 90° will result in an attenuation factor of up to 34 dB in signal strength. By pairing two complementary polarizations, this scheme can immunize a system from polarization mismatches that would otherwise cause signal fade.

The key thing it to experiment and once you provide some degree of diversity as described above. The “APPLY AUTO” button in SDRuno will select the optimum combination of amplitude and phase to give you an enhanced signal versus either one of the individual signals.

The second application is for local noise cancellation. Here you are using manual control of the phase and amplitude to subtract the unwanted interference from the wanted signal. There is already one very good YouTube demo out there which was made by ICAS Enterprises, one of our Japanese resellers: https://youtu.be/2ptiTxU2wMU

The author writes as follows:

This is an experiment showing how to cancel local noise appearing around the FT8 freq on 20m band with a combination of SDRuno V1.32 and RSPduo.

Background: Weak signals (and even stronger ones) are buried under the local noise at FT8 freq on 20m band.

Solution: With the use of the SDRuno V1.32 and RSPduo, the noise can be theoretically canceled.

Rig Setup: An LZ1AQ active loop is connected to Tuner 1 of RSPduo, and a 4.7VDC operatable active whip connected to Tuner 2 respectively. LA1AQ: 15m abg, Active Whip: 17m abg – Two antennas placed about 5m apart.

What you can see in that video:

0″-10″: You can observe strong noise both on Tuner 1 and Tuner 2 (SINGLE mode).

11″- : Switched to DIVERSITY mode.

20″-35″: The active whip connected to Tuner 2 is run by T-Bias 4.7VDC supplied from RSPduo, but when the mode is switched from SINGLE to DIVERSITY, the basic settings will be reset, so there will be no 4.7VDC supplied even if the BIAS-T button is inverted after the mode change. During this period, the spectrum shown is from Tuner 1 only. So, there will be no change in the noise level even if the “APPLY AUTO” is pressed or the ampl/phase manually adjusted. Anyway, you see the big noise is there!

36″- end: Toggling twice the BIAS-T button, you can get the Tuner2 antenna working. When manually adjusting the ampl/phase to the point where the noise becomes minimum, you can see some signals are floating up with much higher readability. When applying “APPLY AUTO”, the noise becomes maximum where weak signals are barely readable. Note: You don’t have to worry about the “BIAS-T” issue when you use any antenna that is NOT of active type. The reason why I am using an active whip is such that it can easily pick up local noises. Also, it is quite easy to set up such a small antenna almost anyplace.

————– end of quotes from the video———————

Please note the Bias-T reset when using diversity is a quirk of the current software release and will be fixed in a future release

We would welcome more practical videos about diversity reception, made by users – we’d love to showcase the best ones on our YouTube channel and add links to them from our applications and support catalogue: https://www.sdrplay.com/apps-catalogue/
You can email links to me at jon.hudson@sdrplay.com

References:
SDRuno manual (see Page 78): https://www.sdrplay.com/docs/SDRplay_SD ... Manual.pdf
Wiki: https://en.wikipedia.org/wiki/Antenna_diversity

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