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Advice for identifying QRM

Discussion in 'Ham Radio Discussions' started by N7CPM, Aug 23, 2018.

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  1. N7CPM

    N7CPM Premium Subscriber QRZ Page

    Hey all,

    I'm looking for a little advice. I am back on HF after almost a year off the air and I've been getting my shack back in order. One thing that I've noticed is that I'm hearing a lot more QRM on my radio and I'm looking for advice on how to identify what it is or its source.

    There are two primary noises I'm hearing: a consistent poping sound and then the noise that travels down the band. The popping is new, as of the last few months, but the other noise I've noticed for the past four years.

    I have uploaded a video with a sample of what I'm hearing.

    My setup is:
    AH4 Tuner (located outside house)
    200' ladder line fed dipole at 80'

    I'm upgrading the grounding in my shack to use a copper plate connected to a ground rod this weekend, but for now I'm connected to a cold water pipe.

    Anyway, I'm just looking for some advice. Thank you very much!

    73 de N7CPM
  2. KK5JY

    KK5JY Ham Member QRZ Page

    Run your radio gear from a battery, then turn off the power to your house. This tells you if the problem is coming from inside or outside your house. If the noise goes away, it's a device in/near your house. If the noise stays, it's outside your house wiring.

    If inside, turn the power back on, but then turn off breakers one-by-one, until you find the branch on which the offending device is running. That will help you narrow it down.

    Since it's still summer, I recommend turning off your A/C before you do this, so your compressor doesn't cycle on and off as you play breaker games. It just saves some wear and tear on an expensive device.

    You can use a portable HF receiver like a TH-F6A with a loop antenna to find the specific device, whether in your house, or somewhere else.

    If the source is coming from elsewhere, the search gets a little tougher, because you need to direction-find the source. A source like a bad power pole or an electric fence energizer can usually be DF'ed using a small yagi antenna on a portable VHF radio in AM mode. Other sources will require a little more detective work to find.
    K3KIC and N7CPM like this.
  3. KA0HCP

    KA0HCP XML Subscriber QRZ Page

  4. W0PV

    W0PV Ham Member QRZ Page

    A couple of observations,

    On the "traveling noise" - at FULL screen size, unless there is some goofy reflection, I see a much weaker but exact spurious harmonic image of it about 35 kHz below the stronger primary signal that crosses the tuned frequency. Although there are iono-sounding transmitters that scan bands to test propagation that produce similar traces, to me this looks and sounds more like a local source, ie, a switching power supply with a drifty oscillator. Follow the previously given traditional methods to find the offender and tame it with ferrites.

    The random wide-spaced popping sounds a lot like STATIC ELECTRICITY building up on the antenna or some other nearby metal equivalent.

    Not to be confused with QRN, ie, static crashes from lightning strikes. Static charges can build on antennas, guy lines, or other wires or metal objects that are isolated from a discharge path to ground, from the friction of rain or other precip, or just wind under favorable WX conditions. These charges can discharge rapidly, arc, through many paths, ie, to nearby objects, tree limbs, across connectors, at random, causing such signals.

    If its not the actual radiating element of an antenna, but a non-radiating supporting structure, mast, house gutters, simply grounding can solve it. However, it may not be coming from your QTH either. Some mobile RDF may be required.

    Sometimes structures like guy lines are intentionally insulated to not interfere with an antenna pattern. Arcing can and does occur across the insulators and can be problematic. "Plumbers delight" construction where elements are not insulted from the boom is inherently grounded.

    The static charge can build up to seriously high voltage levels on antennas and cause damage to radios if conducted down to the shack. They can be mitigated with suitable suppressors, gas-discharge tubes, MOV's, RF choke to ground, etc, home-brewed or commercially available.

    Here is a vid showing a dramatic example of snow static,

    Insulators arcing at commercial tower,

    Last edited: Aug 23, 2018
    N7CPM likes this.
  5. W0PV

    W0PV Ham Member QRZ Page

    I saw a news report about the terribly dense SMOKE POLLUTION in Seattle caused by the regional wildfires. If you are getting that too, the much higher dose of particulates in dry air could make it more likely to generate frictional static charges from winds. That could explain why the noise started up recently.
  6. KY5U

    KY5U Premium Subscriber QRZ Page

    It's QRN not QRM!

    = Noise

    QRM = Intentional interference.
    Last edited: Aug 24, 2018
  7. N2EY

    N2EY XML Subscriber QRZ Page

    QRN is interference from electrical noise, natural or man-made.

    QRM is interference from other stations, intentional or unintentional.
  8. N7CPM

    N7CPM Premium Subscriber QRZ Page

    Thank you very much for your advice! So I learned some valuable things here. I did turn off the house power and ran on emergency power for testing. The "popping" noise disappeared. I slowly started to turn on breakers and it turns out the noise was coming from an older refrigerator I have the garage that was added a few months ago before I was back on HF. Now I get to figure out how to reduce that noise :)

    The traveling noise is still there but I've noticed that since I first got on HF in 2014, so maybe that's just something that I'll have to live with.

    Again, thanks for the advice W0PV!
    W0PV likes this.
  9. N7CPM

    N7CPM Premium Subscriber QRZ Page

    I appreciate the information. One of my favorite parts of our hobby is learning new things and not being afraid to be corrected. Thanks for the clarification.
  10. K3KIC

    K3KIC Ham Member QRZ Page

    A lot of my noise problems were eliminated with line cord ferrites. I'd put one on the frig line cord first. Easy, low cost, high percentage thing to try.
    As a regular noise prevention I put ferrites on all the line cords to my ham equipment. And I have them on the DC power lines as well.
    And on USB cables I use with the rig. And on computer power supply cords.

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