Diversity Operations

K9RX
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Re: Diversity Operations

Postby K9RX » Mon Dec 04, 2017 4:50 pm

as I had said I understand how it is suppose to work - and as such it most definitely could improve things if both antennas are used and say the polarization is changing and i have 2 antennas to take advantage of that - I can add to that contrary to your comment and suggestion it DOES work on HF - I know - I have experienced it nightly on 160 and 80 using both antennas ... I would however wholeheartedly agree that the antennas used matter a great deal.

BUT what I have also seen is improvement with RX1 muted .... so please - don't just say "its all in your head" ... implying some lack of objectivity on my part ... I can honestly say there ARE bugs in the software - there ARE anomalies in the software - I've had strange things happen ... I'm being open minded and working with the developers as I can and as they allow me (some of the recent additions/corrections/changes were from me) ... and I'm wondering IF there is something else going on. I AM trying to be objective. Lets try to stay on the same page - a better answer might have been "if indeed you are hearing something then I don't know what is causing it!" ...

Gary

what antennas have you used for SD on HF, specifically 80 or 160 where you've drawn this conclusion that it isn't effective ?
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w-u-2-o
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Re: Diversity Operations

Postby w-u-2-o » Mon Dec 04, 2017 5:32 pm

OK, Gary: if indeed you are hearing something then I don't know what is causing it! ;)

Because there is no magic in SD. It's exactly the same as MultiRX except the receivers are phase locked.

I've never used SD. There is no point for me. My antennas are so radically different that there is no comparison, one is always substantially better than another. On 160, 80 and 60 I use an inverted L. On 40M a wire half square. On 30 and up a multi-band dipole. Although I generally listen to 40 and below on the half square as it is much quieter with superior SNR to the L. Once in a while on 60M the L will work well, but again it's glaringly evident, no SD required.

73,

Scott
K9RX
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Re: Diversity Operations

Postby K9RX » Tue Dec 05, 2017 12:07 am

My point was that I was trying to find out what it did - when one invoked SD, what does it do other than phase lock the receivers? Does it do anything to the AGC for example as that could account for the change. Note although the perception is I'm hearing an increase in S/N, albeit very small, it might actually be that when it is turned on its "right" and when off something else is different causing a loss of S/N! Thus my question on what is going on - I DO know that there's nothing magic to SD and you can't get any more than the max of any one antenna at any time...

and it might well be a coincidence relative to QSB - although I've 'heard' it a few times now prompting the question.

thanks for the reply.

Gary
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w-u-2-o
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Re: Diversity Operations

Postby w-u-2-o » Tue Dec 05, 2017 1:42 am

AFAIK it does nothing but phase lock the receivers. Everything else remains under the operator's manual control.
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EA1DDO
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Re: Diversity Operations

Postby EA1DDO » Fri Jan 26, 2018 5:12 pm

Hi Scott, all,

I remember when you said:

As a group we are still not fully exploiting the synchronous receiver capability inherent in these radios. Instead we continue to rely on constructs such as so-called "phasing harnesses" or "array controllers", all of which use coaxial delay lines of fixed values to obtain a fairly limited set of phase relationships and therefore a fairly limited set of beam (antenna pattern) configurations. Examples include the venerable four-square array, as well as the stacked yagis of those seeking to control elevation angles. I look forward to a future where such "array controllers" are replaced by multi-channel amplifiers backed by SDR-based synchronous transmitters and receivers.


If we have, let´s say, two antenna (or more), and we place a SDR at his feed point. I can see one of the key points is to get them working in a coherent way.
Sharing the same oscillator is not doable because they will be located at some distance. So I wonder if we can get a central timing system, then feeding this sync to every SDR somehow.

I have no idea if something like "IEEE 1588v2 Precision Time Protocol" could be enought to achieve the target.

https://en.wikipedia.org/wiki/Precision_Time_Protocol

I am thinking in a central GPSDO connected to a IEEE1588v2 ethernet switch, then fibreoptic LAN to the SDR located at the antennas.

Check this small article:

https://turbofuture.com/industrial/An-Introduction-to-Software-Defined-Antennas

What are your thoughts?

Thanks

73, Maximo
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EA1DDO
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Re: Diversity Operations

Postby EA1DDO » Fri Jan 26, 2018 5:54 pm

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w-u-2-o
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Re: Diversity Operations

Postby w-u-2-o » Fri Jan 26, 2018 9:20 pm

Maximo,

To be coherent, or phase and sample synchronized, you have to be much, much better than that.

Let's take a 20M frequency for example, say 14.2MHz. At that frequency, a 10 degree phase shift is equivalent to approx. 2nS.

That is why both ADCs need to be clocked from the same sample clock, and clocked at the same time, i.e. there should be no differential delay between samples.

Now our radios do allow for an external frequency reference, so you could feed each one from the same reference using a set of matched length cables. This would at least get everything on the same timebase. BUT...the radios have no mechanism for synchronizing their sample times.

That said, if you had two radios, both locked the same 10MHz reference, and two data streams, theoretically they would be phase locked at some random phase. You could then simply guess at the phase difference you needed to steer a beam by trail and error until you got what you wanted. With only two radios and two antennas this would not be too difficult. Indeed, that's what we currently do in our current dual ADC radios. Even though they are phase and sample locked, we just guess. However in your picture you have three antennas. That would be darn near impossible to guess at.

73,

Scott
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EA1DDO
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Re: Diversity Operations

Postby EA1DDO » Fri Jan 26, 2018 10:15 pm

That is why both ADCs need to be clocked from the same sample clock, and clocked at the same time, i.e. there should be no differential delay between samples.


So, there isn´t any way to clock two separated SDR ?

Perhaps.... a NCO ?

https://en.wikipedia.org/wiki/Numerically_controlled_oscillator
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w-u-2-o
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Re: Diversity Operations

Postby w-u-2-o » Sat Jan 27, 2018 1:49 am

Certainly there are ways to do what you want, just not with the hardware and firmware that exists in any openHPSDR architecture radio, including Apache Labs radios.

There would need to be a sync signal in addition to the 10MHz, and it would need to be accurate to around +/-1nS, and/or there would need to be a way to calibrate the various receivers using a calibration signal to measure what the differentials are.

73,

Scott
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EA1DDO
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Re: Diversity Operations

Postby EA1DDO » Sun Jan 28, 2018 3:36 pm

Then, an easier way; 2x SDR boards (Hermes, Orion, etc.), sharing clock, in same enclosure, let´s say back-to-back.
This way you get two coherent boards, with two coherent receivers and two coherent transmitters, starting point for beamforming.

GPS is not mandatory.

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w-u-2-o
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Re: Diversity Operations

Postby w-u-2-o » Sun Jan 28, 2018 5:08 pm

Yes, you'd have to modify the boards to allow a single board to supply the same ADC clock to all ADCs. I have not studied the problem. Surely not a difficult technical challenge, however you may have to devise a buffer/driver circuit to ensure signal integrity.

Then there is the problem of writing firmware and software to exploit this hardware. There would need to be sufficient time tags embedded in the IF data streams to be able to match up the streams on a sample basis coming from multiple radios. Again, not a difficult technical challenge, there are thousands of DF systems around the world that do exactly that .

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