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    Local QRM / noise canceller

    Posted In: Technology

    • Visitor
      Anonymous he March 25, 2018 at 15:57#11486

      Hello,

      I received a tip from a known person about a 'noise canceller'. They are made by MFJ and the price is around €200. It's a significant investment, so I want to ask if there's anyone on the forum (or if anyone knows someone) who owns such a device and would be willing to lend it to me for a trial with financial security.

      I also found instructions on the web on how to make a noise canceller, but I have no practical experience with it and I'm afraid of failure, or the amount of time invested compared to usefulness.

      Thank you for the responses.
      OM0ATV

      Reply
      Visitor
      Anonymous he March 25, 2018 at 18:37#14977

      Hello,

      1; why don't you use your callsign? If you don't have one, please at least write that you are a listener.

      2; maybe a receiver for ROB on 80m would help you, because removing QRM is always better than some NR and similar nonsense.

      OM4TW
      stefan

      Reply
      Participant
      om1aeg he March 25, 2018 at 20:33#14978

      Hello, Vlado OM5KV has experience with NC, contact him. He has a simpler wideband one. A more suitable NC is tuned to a narrow band, where it works, which the MFJ is not.

      It seems easier to me to find the source of interference, if you have a Tescun, then make a magloop from harder coax (or AL pipe for heating) and a tuner from an old transistor radio, the loop has a very sharp minimum of about 10-20 degrees and the interference can be found by triangulation in a village environment. Or use the loop for reception and minimize the interference. On vacation in 9A, this loop was able to reduce the noise from the neighbors' LCD TV from S5-S7 to S0 on the 40m band with proper orientation. The downside is that desired signals from that direction are also much weaker.
      https://rsars.files.wordpress.com/2013/01/simple-rg213-hf-loop-30m-15m-g8 from e-iss-1-31.pdf

      Reply
      Visitor
      Anonymous he March 31, 2018 at 12:27#14979

      Noise canceller, it's a kind of crutch that may or may not help.
      It is good if the interference has a stable character, does not travel, and cannot be removed otherwise.
      The most common problem today is often interference from impulse sources and inverters, or modern electronics.
      Many interferences come from permanently powered devices, such as charging adapters, clocks in appliances like microwaves or stoves, or from sources that are in sleep mode, not just TVs, hi-fi, PCs, but also in various utilities, such as pumps in wells, or their electronic circuits, such as frequency converters, level indicators, automatic irrigation systems, garage doors, automatic gates, sometimes even alarms, or twilight or motion-controlled lights, the more modern, the often worse.
      For measurement, often neither Mag nor loop is needed, because it is a very selective antenna that is more suitable for the input of a noise canceller, tuned in the area, to the maximum disruptive signal.
      If you have a panoramic receiver, it is better to plug a connector into the input of the external antenna and use a linear attenuator, or at least a potentiometer as an attenuator and a piece of wire.
      When approaching interference, sensitivity can be reduced and further searched.
      The attenuator or its potentiometer looks something like this..
      https://sortec.sk/ikusi-fav-920_d2679.html
      Basically, it can also be replaced with a dual 100R or 250R potentiometer, for HF there is no problem, even if it has a metal casing.
      I wouldn't be afraid of the interference removal service because that interference and its possible removal is important for others in your area too.

      Reply
      Visitor
      Anonymous he April 1, 2018 at 8:41#14980

      I don't know, I have a very simple device with an attenuator at the input, but it doesn't seem very useful to me, when it roars, I just lower the volume, or I take a box for another frequency.

      I observe large differences in the intensity of interference, e.g., on 3550 it is usually significantly less than on 3560; perhaps this is also because the other frequency is QRP, which could mean that the source of QRM is the local tamaters.

      Reply
      Participant
      ok1uhu he April 1, 2018 at 14:48#14981

      @norbertx wrote:

      I don't know, I have a very simple device with an attenuator at the input, but it doesn't seem very useful to me, when it roars, I just lower the volume, or I take a box for another frequency.

      Even better is to plug your ears, ideally with a nail. Perfect attenuator.

      @norbertx wrote:

      I observe large differences in the intensity of interference, e.g., on 3550 it is usually significantly less than on 3560; perhaps this is also because the other frequency is QRP, which could mean that the source of QRM is the local tamaters.

      Samozřejmě! Při přesném změření totiž zjistíme, že střed rušení je přesně na 3553kHz. Numerologicky pak odvodíme, že 3 a 5, stejně jako 5 a 3, dá dohromady osmičku, 3553 tedy znamená 88, což je mystický symbol PRO Heil Hitler. Ruší tedy dávné nacistické vysílače, skrz díru v časovém kontinuu.

      Norbert, you are really an incredible dilettante.
      Incredible.

      Reply
      Participant
      om5na he April 2, 2018 at 8:51 PM#14982

      Hi, try to look at the QRM eliminator from WIMO as well. A few links on how it works: https://youtu.be/Kj-igyVGZ4I,https://youtu.be/BdmbsnCoy9w,http://www.amateurradio.com/noises-off-wimo-qrm-eliminator/,http://www.eham.net/reviews/detail/11503.

      But if you really want something cheaper, try one kit 'QRM Eliminator X-Phase (1-30 MHz) HF bands', it is also sold assembled...

      73, om5na 8)

      Reply
      Participant
      om1aeg he April 3, 2018 at 8:53 PM#14983

      Noro
      http://nerdsville.blogspot.sk/2014/08/noises-off-wimo-qrm-eliminator.html

      Reply
      Visitor
      Anonymous he April 4, 2018 at 4:03 PM#14984

      ... I have been successfully using this QRM eliminator for a few years on HF, the construction is not complicated, as a helper antenna I use a VHF antenna located about 8m away from the HF antenna, at first I didn't trust it much, but it surprised me with its effectiveness, it eliminates almost everything except the elevator, hi that had to be eliminated separately, hi....
      .... inspiration for DIY enthusiasts.....: http://www.dl0hst.de/dateien/technik/DG0KW_X-Phase_2_v14.pdf

      ... the PCB is not a problem to print on a laser printer and transfer to PCB + etch.... good luck.....Daniel, OM1DS

      Reply
      Participant
      om1aeg he April 4, 2018 at 8:01 PM#14985

      For construction, there is a nice overview of 'QRM eliminators' here:

      http://www.g8jnj.net/rfnoisecancellati he .htm

      I like the most http://users.tpg.com.au/users/ldbutler/NoiseCancelling.htm for its minimal impact on the signal from the main antenna (no active component in the path) and for the combination of preselector and phase member at the input from the 'noise antenna', unlike circuits where there are active components in the path from the 'main antenna' and everything is broadband with the possibility of intermodulation products outside the currently listened band. The disadvantage (but also an advantage) is the necessity to 'tune' according to frequency and also the inserted attenuation (against 'active' circuits).

      Reply
      Participant
      om3tix he April 6, 2018 at 5:50 PM#14986

      I do not want to advise anyone on how to proceed in identifying any interference, whether TV or amateur radio service, but if the troubled radio amateur made an effort to solve this problem directly with the neighbors and it was unsuccessful, I would immediately report it to the interference service, as we have the right to do so by law.
      And not to produce various interference filters and suffer with it, more or less unsuccessfully.
      This type of interference looks like from a plasma TV, but it can also be anything else, but the interference service will find out what it is and focus on it.
      Similarly, a lot of interference comes from amateur radio stations, especially during contests on VKV and up. But everything will come to an end, and even the big gun multi beaming switching masters of Slovakia will come to an end. Nothing lasts forever, not even love for one girl. Let's not let shit go to our heads.GL

      Reply
      Participant
      ok1rr he April 10, 2018 at 8:05 AM#14987

      In the overwhelming majority of phase shifters, the biggest problem is the fact that the signal vector we want to suppress cannot be rotated within a range of +/- 180 degrees. Therefore, 'unsuppressable' signals occur. The second problem is that when changing both amplitude and phase, the amplitude of both signals changes, i.e., both the desired one and the one that is to be suppressed. Thus, the phase shifter also acts as a variable attenuator. We certainly do not want that; the ideal state would be if we could rotate the phase completely without affecting the amplitude of the desired signal. The third problem is somewhat delicate settingsof amplitude and phase controls, where a slight turn of the knob is enough for everything to go wrong. In most circuits, the change in phase depending on the knob's rotation is strongly nonlinear, and the same more or less applies to amplitude.

      PA0SIM offers an interesting solution:
      http://www.pa0sim.nl/Phaser%2080%20-%2010%20meters.htm

      Definitely worth trying.

      73, Martin, ok1rr

      Reply
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