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Author Topic: How MFJ-1026 knows noise from signal?  (Read 211 times)

N3WTK

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How MFJ-1026 knows noise from signal?
« on: February 19, 2021, 10:17:28 PM »

Something I've wondered about is how does the MFJ-1026 differentiate between noise and signal. I mean, you set up a reference antenna for the noise, but nothing prevents that reference antenna from also receiving signal (just like your main antenna receives signal and noise). So if the 1026 cancels noise, how then does it not also cancel the signal?

Indeed, that seems to be what's happening for me. See my other post here on this forum for the full background. Before I learned that it's probably common mode I ordered an MFJ-1026. The MFJ-1026 arrived today so I set it up and tried it.

The noise reference antenna is an original Ukrainian active Mini Whip from the transverters-store.com. Although the MiniWhip instructions say to ground the PCB at the mast, if I do that then the antenna has no noise, so I leave off the PCB to mast ground wire so that it is noisy like my signal antenna. The signal antenna is an AlphaAntenna 10-160m HF JPole Sr.

Tonight the noise was only about S7 (reduced as a result of a pair of air chokes I kludged). I am able to adjust the 1026 to cancel the noise; how about that, it works! Or does it? Because although it cut out the white noise, it seems like it's blanking the signal, too, because the signal doesn't appear to be any stronger without the noise. Or am I doing it wrong? Or maybe the 1026 doesn't work on this type of noise? You can watch and listen to the results in this video here. I've already adjusted the 1026; what I'm doing in the video is turning the power on and off so you can see the effect of it in and out.

In any case, the original question remains, how does the 1026 differentiate between noise and signal?
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Dave / N3WTK

G4AON

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Re: How MFJ-1026 knows noise from signal?
« Reply #1 on: February 19, 2021, 11:33:19 PM »

The MFJ works by adjusting the phasing between antennas, if the signals are out of phase they cancel out.

As you found, stopping noise from your system with common mode chokes on the feeder, or using an active antenna away from electrical wiring, is far easier than phasing out noise, the latter should be regarded as a last resort to deal with a nearby specific noise, such as a rogue switched mode supply or a plasma TV.

You can completely phase out local medium wave broadcast stations, which is a good way to get used to these sometimes awkward to use devices. They are not effective against wide band “hash” that can be radiated by overhead wiring.

I have an MFJ 1026, but since a neighbour moved and took their lousy TV, I’ve not needed it. It is worth keeping in case some other noise pops up.

73 Dave
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W9IQ

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Re: How MFJ-1026 knows noise from signal?
« Reply #2 on: February 20, 2021, 04:27:13 AM »

Something I've wondered about is how does the MFJ-1026 differentiate between noise and signal. I mean, you set up a reference antenna for the noise, but nothing prevents that reference antenna from also receiving signal (just like your main antenna receives signal and noise). So if the 1026 cancels noise, how then does it not also cancel the signal?

It comes down to the difference in signal strength. The reference antenna should have less gain or less favorable directivity than the main antenna. Since the noise is local, both antennas will pick that up nearly equally allowing good cancellation but the reference antenna won't (shouldn't) pick up the desired signal as well so it results in only a partial "cancellation" of the desired signal.

- Glenn W9IQ
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- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

W1VT

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Re: How MFJ-1026 knows noise from signal?
« Reply #3 on: February 20, 2021, 07:05:12 AM »

It doesn't, which is why I run two 4 element Flag arrays into my null canceller.  I can choose the one aimed at the desired station as the "main" antenna and I can choose one that picks up the noise best as the "auxilliary" antenna.  I could also choose an antenna that has a rear null aimed at the desired station as the "auxilliary" antenna.
If necessary, I also have a close in antenna aimed at the power lines that I could patch in as the "auxilliary" antenna.  One of my projects is to install a BNC switch to patch in more RX antennas.

Last summer I ran long feedlines to put all eight of my RX Flags in reasonably quiet locations.  The RG-6 needed to run eight long feedlines cost less than $100.  I can afford that. 
The system works well enough that I hear most European stations a lot better than they hear me, even when I'm running the amp.

Zak W1VT
« Last Edit: February 20, 2021, 07:11:20 AM by W1VT »
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N3WTK

  • Posts: 84
Re: How MFJ-1026 knows noise from signal?
« Reply #4 on: February 20, 2021, 08:45:20 AM »

Okay, that all makes sense, and it's all consistent with the fact that when the MiniWhip is "properly" installed with its ground connection, it doesn't work as an effective reference antenna to cancel the main antenna's noise. I may play with various, less-efficient noise antennas, while I'm waiting for the ferrite to arrive which will (hopefully) get at the real source of the problem.
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Dave / N3WTK
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