Diversity - how does it work?

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g4enz
Posts: 40
Joined: Tue Nov 29, 2016 1:17 pm

Diversity - how does it work?

Post by g4enz » Wed Jul 10, 2019 9:59 am

I admit to being rather confused by the new Diversity functionality that arrived with V1.32. I thought I might not be alone and hope that someone can explain how Diversity in SDRuno works.

I have one other system that supports Diversity reception and that is my K3 equipped with a second receiver. When the K3 is in diversity mode, the demodulated audio from each receiver is produced to either the left or the right channel of the output audio. When wearing headphones, the result is that the CW or SSB signal I am listening to moves around from ear to ear as the signal fades at different times on the different antennas. With the K3 it is immediately clear to me what is happening as my brain does the job of integrating the two received signals.

SDRuno is doing things in a different way, but, I am not sure exactly what it is doing. The major difference is that I get a single output and a display showing two values for phase and two values for amplitude. These phase and amplitude values are constantly changing as, I assume, the arriving signals on my two antennas are changing. I also assume that SDRuno is making decisions about how to produce an optimal result from the two supplied signals but, what are the criterion that it is using?

At the moment, I am parked on the 40m WSPR frequency, experimenting. I have a doublet on one port and a vertical on the other. Normally, I will decode a few unique stations on the vertical and a different few unique stations on the doublet. When Diversity reception combines the two antennas, what should I expect? Should I now decode the "super-set" of the two antennas? Or does it not work like this?

Martin - G4ENZ

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Tech_Support
Posts: 491
Joined: Mon Jun 01, 2015 7:00 pm

Re: Diversity - how does it work?

Post by Tech_Support » Wed Jul 10, 2019 11:27 am

Hello Martin,
The type of diversity implemented in SDRuno is called Maximal Ratio Combining Diversity (MRC Diversity). See: https://en.wikipedia.org/wiki/Maximal-ratio_combining

With the correct antenna setup, this can give you an improvement in SNR, particularly in a fading environment.

What you describe is something quite different, but can easily be set up using the RSPduo and two instances of SDRuno with the audio from one channel piped to the left channel and the audio from the other instance piped to the right channel.

Sincerely

Tech_Support

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g4enz
Posts: 40
Joined: Tue Nov 29, 2016 1:17 pm

Re: Diversity - how does it work?

Post by g4enz » Wed Jul 10, 2019 12:11 pm

Hi Tech_Support,

Thank you for your swift response. I hadn't heard of MRC Diversity and unusually the Wikipedia reference has left me only a little wiser. When MRC talks about "channel", what does that refer to in SDRuno terms. Is it the whole captured spectrum or the just the bandwidth that I am currently demodulating? If it's the later, what happens when I run multiple receivers?

When you say that the K3 type of Diversity can be easily set up in SDRuno by using two instances and piping the audio accordingly. Does that mean there is some way of synchronising the two Duo instances so that they can be tuned together? If there is, I have never found it and without that, the solution you describe is very awkward to use.

Regards,
Martin - G4ENZ

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glovisol
Posts: 658
Joined: Thu May 10, 2018 6:42 pm
Location: Piedmont, Italy

Re: Diversity - how does it work?

Post by glovisol » Wed Jul 10, 2019 12:45 pm

Look here:

https://www.sdrplay.com/community/viewt ... 068#p16068

You must go click on SINGLE it will open up so you can click on DIVERSITY. Then it will be all automatic, provided you have two different antennas, one for each 50 Ohm tuner input. You will not believe it, it takes time to get used to dreams when you are awake!

Do enjoy:

THE DIVERSITY AGE HAS ARRIVED!

glovisol

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OH2BUA
Posts: 80
Joined: Mon Aug 29, 2016 8:58 am

Re: Diversity - how does it work?

Post by OH2BUA » Wed Jul 10, 2019 1:09 pm

Hi,

I'm not willing to hijack the thread, but adding a closely related question, I think:

The manual says "HiZ port is not available for Diversity mode". Is that a fundamental, permanent thing, or is it possibly changing in foreseeable future?

I ask due to my antenna planning matters.

73, Jukka

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Tech_Support
Posts: 491
Joined: Mon Jun 01, 2015 7:00 pm

Re: Diversity - how does it work?

Post by Tech_Support » Wed Jul 10, 2019 1:21 pm

Hello Martin
Hi Tech_Support,

Thank you for your swift response. I hadn't heard of MRC Diversity and unusually the Wikipedia reference has left me only a little wiser. When MRC talks about "channel", what does that refer to in SDRuno terms. Is it the whole captured spectrum or the just the bandwidth that I am currently demodulating? If it's the later, what happens when I run multiple receivers?

When you say that the K3 type of Diversity can be easily set up in SDRuno by using two instances and piping the audio accordingly. Does that mean there is some way of synchronising the two Duo instances so that they can be tuned together? If there is, I have never found it and without that, the solution you describe is very awkward to use.

Regards,
Martin - G4ENZ
The MRC diversity function is applied to the entire viewable spectrum. As things stand, it is not possible to lock the tuning of two separate instances of SDRuno together.

Sincerely

Tech_SUpport

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glovisol
Posts: 658
Joined: Thu May 10, 2018 6:42 pm
Location: Piedmont, Italy

Re: Diversity - how does it work?

Post by glovisol » Wed Jul 10, 2019 1:22 pm

To get the HI Z port going would be really tops!!!

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Tech_Support
Posts: 491
Joined: Mon Jun 01, 2015 7:00 pm

Re: Diversity - how does it work?

Post by Tech_Support » Wed Jul 10, 2019 3:07 pm

Hello folks,
There is a problem in using the Hi-Z port in that the gain line-up and gain steps are completely different to those of the 50 ohm ports. For diversity to be effective, it is necessary to scale the two paths such that the levels are equal and then they are combined with the appropriate phase relationship. This is something that we are not sure will be possible with the Hi-Z port. We are not ruling it out for the future, but for now we decided to exclude it from release 1.32.

Sincerely

Tech_Support

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