Radio Frequency Interference (RFI) or noise, has become one of the single largest impediments to HF operation in any urban environment.  This article covers the basic philosophies to help you identify and (hopefully) resolve your noise issues.

This is not about throwing your arms up in despair and moaning “every time I turn on 40m I have horrendous noise”.  RFI in some urban environments may appear unsolvable, but it is hoped that by working through the methods and techniques presented herein, you will at least be able to improve your on-air enjoyment.

Interference may take many forms and dealing with it is a process that must first start with a broad view, then progressively focus in on the specific issues. It can become complex and there are many dead-ends to avoid.  The aim of QRM.guru is to guide you through the labyrinth of information to hopefully find a meaningful resolution to the problem.

Resolution may take several forms.  It may involve technical investigation, negotiation with neighbours, consultation with a public utility, referral to the ACMA or a combination of the above.

One aspect is certain.  The onus for commencing action lies with the operator.  Service providers and the public regulator will only take an interest if preliminary work has been done properly and if they have been approached in just the right way.  Support resources of the ACMA are extremely limited and they will only engage where there is a likely chance of success.   The correct method of seeking administrative assistance is an important part of this resource.

At the completion of “Basic Diagnosis” you should start to have a profile and better understanding of the characteristics of the problem.  This noise profile provides the basis for moving to “Identifying the noise source”.

A simple DF loop antenna and receiver can make a great tool for locating an interference source

Sometimes you need to ask “what isn’t it?” rather than “what is it?”.  The latter leads you to make assumptions – and we all know what happens when you make assumptions.  Start with a very simple journal and make notes about the noise.

We hope to provide you with a methodology and set of tools to work through the process of identification, diagnosis and resolution.  Some solutions may be expensive and/or require out-of-the-box thinking.  We live in an ever more complex world with dirty RF devices infecting just about every facet of our amateur radio lives.

From day one you must keep a journal or diary to log your activites.  There are various other forms you can use to help you narrow down and diagnose the noise source, but a journal will provide a chronological reference of all your activities, including, but not limited to:

  • key events (eg. new equipment, neighbour installing new equipment)
  • diagnosis or investigations your have undertaken
  • visits to or discussion with neighbours
  • calls to power companies

In this post we aim to help you with basic diagnosis.  You should be able to identify and profile the noise characteristics. You should have some basic facts about the noise and be able to answer the following questions:

  • What is the actual issue to be resolved?
  • Is a neighbour complaining?
  • Is the noise affecting your radio station?
  • What bands are most effected?
  • Does the noise have a profile?
    • Time of day
    • Direction
    • Intensity
    • Frequencies/harmonics
  • What time of the day/night is the noise at its worst?
  • Have you observed the noise on more than one receiver? (thereby ruling out an internal birdie)
  • Record the noise and try comparing it to known noise sources – refer this link.
  • Have you observed if the noise is aligned with any routines in your household? (eg. Cloths washing, reading lights, computer use, daylight hours only etc.

Once you have a profile of the noise you will then want to narrow down the source to one of two possible sources:

  1. RFI internal to your property
  2. RFI external to your property

Perhaps the simplest way to narrow down the noise source is to determine whether it’s internal to your property first.

Follow this very simple procedure:

  1. Setup your receiver to operate on an independent power source (12v battery)
  2. Confirm you are still receiving the noise
  3. Turn off the mains master switch
  4. If you are no longer hearing the noise then the source is local to your property. Work through a simple procedure to narrow down the noise source in your home.  Start here.
  5. If you are still hearing the noise, then it is external to your property. Your nex step is to locate the noise source.  Start here.

The following video provides an introduction to dealing with interference,