Noise cancelling / Phasing using diversity

Taiga
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Noise cancelling / Phasing using diversity

Postby Taiga » Sun Dec 27, 2020 7:10 pm

Hi,
Has anyone used the Diversity feature in Thetis in order to emulate the noise function of popular phasing / noise reduction units such as the MFJ-1026, QRM-180, ANC-4, NCC-2 or Quantum phaser?

If so, could you kindly reply w/ how you did it, including the type of noise antenna you used? Will Thetis / Anan automatically protect the front end of RX2 during transmit, if RX2 was being used as a noise antenna input? Seems like it almost certainly will, but am asking because this is potentially a source of catastrophic failure.

If it works, could be an exceptionally useful feature for those of us operating in urban environments.

To the mods - I posted this in the "Thetis" section because noise reduction is a general topic of wide ranging interest, compared to the more common use of the diversity feature to steer multiphased antenna arrays. Please move this post to the 'Diversity" section if that is more appropriate.

73,
Taiga
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w-u-2-o
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Re: Noise cancelling / Phasing using diversity

Postby w-u-2-o » Sun Dec 27, 2020 10:30 pm

Taiga wrote:Hi,
Has anyone used the Diversity feature in Thetis in order to emulate the noise function of popular phasing / noise reduction units such as the MFJ-1026, QRM-180, ANC-4, NCC-2 or Quantum phaser?
I can't speak to all those devices, but the MFJ-1026, Quantum Phaser, NCC-2 and ANC-4 do exactly the same thing as "Diversity" in PowerSDR and Thetis. So there is no "emulation", they are all purporting to do the same thing, which is to vector sum the outputs of two receive antennas with variable phase and gain factors, i.e. coherent beamforming. In other words there is nothing special you need to do in order to accomplish the same thing the MFJ, NCC, Quantum and ANC units are doing (and perhaps the other as well but I am not familiar with them).

Will Thetis / Anan automatically protect the front end of RX2 during transmit, if RX2 was being used as a noise antenna input?
If ground RX2 on TX is turned on, yes. However I strongly recommend using an external RF limiter like the DX Engineering "Receiver Guard". It's "cheap insurance".

If it works, could be an exceptionally useful feature for those of us operating in urban environments.
It does work, but only for coherent, interfering signals from a point source in the far field. Did you read this thread: viewtopic.php?f=21&t=2362 ??
To the mods - I posted this in the "Thetis" section because noise reduction is a general topic of wide ranging interest, compared to the more common use of the diversity feature to steer multiphased antenna arrays. Please move this post to the 'Diversity" section if that is more appropriate.
Moved it ;)
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kc2rgw
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Re: Noise cancelling / Phasing using diversity

Postby kc2rgw » Sun Dec 27, 2020 11:28 pm

I don’t have two identical antennas to phase, but I do use Diversity to cancel noise sources from my own house.

It only works on one source so if you have multiple it’s not going to affect them all.

I use a really crappy fan dipole I made for broadcast FM, 2m and 440 that just hangs in my shack as my “noise” antenna.

It works very effectively to null out the broad band noise the fan motor controller my heat pump generates, and will drop the S5 noise floor over an S3 without it running, down to the S3.

When idle, that same heat pump has a horrific noise the control board radiates and it will greatly reduce the harmonics of that noise...but remember it’s single source so you have to pick the biggest offender and settle for reducing that influence.

I have both an Anan 7000 and a SunSDR2 DX and go between them both frequently. Diversity is a major advantage as well as Pure Signal and being able to listen to multiple antennas...all because the Anan has two ADCs in it. These are the things that give the Anan the edge over the Sun for me.
K1LSB
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Re: Noise cancelling / Phasing using diversity

Postby K1LSB » Mon Dec 28, 2020 1:05 am

I use Diversity often to eliminate single-point noise sources, it works superbly. I was using it on 40 meters today to remove a roughly 3khz-wide 30db spike and was easily able to remove literally all evidence of the intruder from the panafall and the received audio....and there was a faint QSO hidden under the spike that suddenly popped out of the background into perfect readability! Awesomely powerful feature....I'll never own another radio that doesn't offer Diversity (or PureSignal, for that matter)....but then again, I'll probably never own another radio except possibly another ANAN, lol.

EDIT: My diversity receive antenna is a simple loop of wire literally laying on the ground. It's roughly 130 feet in circumference, feeding into a coax with a 3:1 isolation transformer. Truly amazing performance, it surprised the snot out of me when I first tried it. It shows very nearly the same S/N ratio as a tuned dipole on all the bands I listen to.

Here's an article on the "Loop on Ground" antenna (though mine's a tad bigger than the one in the article):

http://www.kk5jy.net/LoG/?fbclid=IwAR0d ... B9h5T4NGyU

Mark
WR4N
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Re: Noise cancelling / Phasing using diversity

Postby WR4N » Sat May 21, 2022 7:24 pm

DISCLAIMER: I am not hesitant about stating that electronics and technology are not my areas of expertise - but I work hard to acquire new knowledge and apply that knowledge.

Now then, I am just now experimenting with Diversity Reception. I have a SteppIR Urban Beam at 45' - that covers 6m-40m (It works as a dipole on 30m-40m) and an 80m Dipole at 36' - but my plan has been to add an 80/40/20m Fan Dipole at 80' (in a tree that is on the opposite side of the house where my tower is placed.)

I recently worked an African station on 40m, at 4:50 UTC. It was virtually impossible to complete the contact, but we were finally able to exchange 3-3 reports. I heard a US station say that the African station was supposed to be on the air the following night, at the same time, on the same frequency. It was then that I decided to try Diversity Reception. The next day, with nothing else to use, I connected my 80m Dipole to Rx2. When I heard the African station, I selected "Enabled" and began to adjust the "Phasing Control." The African station seemed to magically rise above all the interference (whatever the source was) and became 100% Readable; additionally, I could hear numerous other stations calling him - stations that I previously had no way of knowing were on frequency. WOW! The bottom line is that I am now working hard to develop my understanding of how to best use Diversity Reception.

QUESTION #1: I assume that because my 80m Dipole had a large capture area, it worked adequately for my purpose. Is this a reasonable assumption?

QUESTION #2: I realize every situation is different, but it seems as if many operators use a loop for Rx2. Is this the best overall, multipurpose receive antenna for my situation as I have described it? If so, I would greatly appreciate input concerning feedline. I have to use coax - is any 50 Ohm coax adequate and what is the best balun to use? Also, I have heard some say they place a loop on the ground, others at 10,' others say to go as high as possible, etc. Finally, some use a 60' loop, with 15' on each side, while I have seen plans that call for giant loops up to 800' (at least for me, that would be a giant loop and not possible). Any suggestions on height for a dedicated Receive Only / Diversity Antenna?

With Appreciation,
David
WR4N
RADIO: ANAN 7000 DLE MK2 (Black Version) Thetis 2.8.11.
PC: HP Desktop - Intel Core i7 (10th Gen) - 16GB memory - 512GB SSD - Intel UHD Graphics 630 - WINDOWS 10 (100% Dedicated to ANAN)
PS: ASTRON 35 AMP (100% Dedicated to ANAN)

Best 73s,
WR4N - David
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w-u-2-o
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Re: Noise cancelling / Phasing using diversity

Postby w-u-2-o » Sat May 21, 2022 9:11 pm

WR4N wrote:I assume that because my 80m Dipole had a large capture area, it worked adequately for my purpose. Is this a reasonable assumption?
No. The reality is you simply got lucky. Since "diversity" in this context = beamforming, you were very luckily able to form a beam in the direction of the station of interest and a null in the direction of some of the interfering signals you might have.

I realize every situation is different, but it seems as if many operators use a loop for Rx2. Is this the best overall, multipurpose receive antenna for my situation as I have described it? If so, I would greatly appreciate input concerning feedline. I have to use coax - is any 50 Ohm coax adequate and what is the best balun to use? Also, I have heard some say they place a loop on the ground, others at 10,' others say to go as high as possible, etc. Finally, some use a 60' loop, with 15' on each side, while I have seen plans that call for giant loops up to 800' (at least for me, that would be a giant loop and not possible). Any suggestions on height for a dedicated Receive Only / Diversity Antenna?
I've not tried this myself, but it would appear that many folks have had good luck with a rotatable mag-loop for RX2. This allows much more flexibility in terms of "getting lucky", since the rotatable mag loop provides an extra dimension to adjust the relative beam patterns of the two antennas prior to phase and amplitude adjustment.
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KA5KKT
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Re: Noise cancelling / Phasing using diversity

Postby KA5KKT » Sun May 22, 2022 2:24 am

On a couple of bands I utilize pairs of similar inverted vees orthogonal to each other. The notion is that inverted vees tend to favor vertical polarization off the ends and horizontal polarization on the broadsides.
VE6EY
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Re: Noise cancelling / Phasing using diversity

Postby VE6EY » Sun Dec 04, 2022 4:48 am

I have done extensive work with both analog and digital diversity reception over the past few years, particularly for simple beamforming and interference cancellation. You can find tons of information and videos about these through my blog Making It Up (at http://play.fallows.ca

In addition to ham antennas, I use a 100' wideband loop array, as well as noise antennas. Receivers include RSPduo, Afedri 2-channel and, of course, ANAN-7000 DLE MKII. Also, you will find direct comparisons with analog phasing boxes X-Phase, ANC-4, MFJ-1026 and NCC-1.

Bottom line is that all the analog and digital approaches do a good job of interference reduction (single point sources, mainly) across HF and acceptable single-lobe/null beamforming on MF and lower HF.

You might also look at my video on Modern Diversity Reception at https://youtu.be/33uJCoTesGc

73 John VE6EY
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w-u-2-o
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Re: Noise cancelling / Phasing using diversity

Postby w-u-2-o » Sun Dec 04, 2022 5:35 pm

VE6EY wrote:I have done extensive work with both analog and digital diversity reception over the past few years, particularly for simple beamforming and interference cancellation.

John,

That's quite a body of work there. In your role as an evangelist for this sort of thing, I would strongly encourage you to make proper use of the term "diversity". Thetis, and PowerSDR before it, do NOT make proper use of this term, This has badly tainted both people's understanding of the various techniques and done a huge disservice to the professional technical lexicon.

"Diversity" always refers to non-coherent (not dependent on signal phase) techniques of improving signal reception. Beamforming is a coherent (dependent on signal phase) process and should never be confused with diversity techniques.

The mislabeling of the feature in Thetis/PowerSDR is one of the worst things that ever happened, and has hopelessly confused the issue for a large population of hams.

Your use of the term "spatial filtering" is a valid one, but one must be extra cautious to make the distinction between a coherent spatial technique, e.g. beamforming, and non-coherent spatial diversity, e.g. merely switching between two antennas to mitigate multipath effects. In general, and in the technical literature and in professional practice, spatial filtering always refers to beamforming.

Finally, there is no distinction between time delay and phase in the RF world. They are one and the same and it's merely a matter of semantics how those terms are used.

73,

Scott

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