A noise blanker is used to combat "impulse" type noise; such as automobile ignition noise. Noise blankers usually have an adjustable threshold setting and narrow noise spikes whose amplitudes exceed this threshold cause a brief interruption in the receiver's internal signal path to eliminate the spike. Noise blankers are usually present in the IF circuitry of the receiver before the high-selectivity IF filters.

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DSP noise reduction operates by examining a characteristic of signals and noise called correlation and dynamically filtering out the undesired noise. Correlation is a measure of the “regularity” of a signal. In most DSP noise blanker implementations, the amount of noise reduction varies according to the correlation characteristics of the noise. Random noise such as white noise or static is uncorrelated. Speech and ignition noise is moderately correlated. Heterodynes and pure tones are highly correlated.

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Answer: Signals which appear across a wide bandwidth

Think of lightning. It is a signal which covers a wide bandwidth as it can be heard in AM or SSB modes on receivers across many frequencies/bands. Noise Blanker helps to eliminate this.

Other wide bandwidth signals include automobile spark plugs, electric motors, generators, or alternators with armatures, electric switches, or anything else that produce sparks.

Memory tip: read "blanker," think blanket. Blankets are wide.

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A Brute Force filter is a ham "slang" term. The term refers to any large, well shielded filter. The answer to this question is easy to remember just remember "Brute Force".

An example of the kind of filter this question is referring to would be: http://www.digikey.com/product-detail/en/20DRGG5/603-1147-ND/1718592

Mind Tickler: Only one answer has the term AC in it.

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Atmospheric static is radio noise caused by natural processes, such as lightning discharges in thunderstorms. At VHF and above they are at lower levels and thermal noise in the receiver is the limiting factor.

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This is commonly the first test that you should accomplish if you experience RFI (radio frequency interference) in your shack. Some call it a battery operated radio RFI test. You eliminate the possibility that RFI is coming from your own location.

This question is similar to question E0A02 which suggests making sure signals from your radio are less than the uncontrolled MPE limits.

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Electrical mains wiring can act as an effective antenna, conducting transmitted signals into connected electrical appliances. These unintended signals are referred to as common-mode noise, which refers to the presence of unintended signals on all AC lines: hot, neutral and ground.

Electrical spark generated signals are caused by gaps in high voltage transmission lines, across which we can have arcing, or by certain types of motors. These are not mentioned in the stem so that answer is incorrect.

AC power line related factors may cause interference on the receiving antenna, but the question is asking about interference being received on the mains wiring, therefore those two choices can be eliminated.

The clue here is a signal is picked up in the electrical wiring, meaning we are discussing a transmission related event. Therefore the common-mode signal generated by radio transmission is the correct choice. If the radio antenna were merely receiving, then we would not expect adjacent wiring to have any induced current.

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When the receiver's noise blanker is turned on and/or set to maximum, strong signals on nearby frequencies may be heard on your frequency as noise or chatter. The audible effect is similar to "splatter," which is sometimes heard when a station operates an improperly adjusted transmitter and generates a signal with excessive bandwidth.

Cheat: IF. Only the correct answer has the word "if" in it.

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Many touch controlled devices contain a crude oscillator with an output rich in harmonics. They operate by sensing changes in oscillator frequency as a hand is brought close to them.

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To eliminate this would require some detective work. Regularity and the times that the problem occurs would provide clues. If it was frequent enough, the old trick of switching off your main house breaker would tell you if it is on your property.

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A computer is full of digital signals. From an RF point of view these are square waves rich in harmonics, hence the large numbers of specific frequencies.

Hint or method to remember the answer: Some hams refer to this noise as "birdies" on the band, which can describe the bird-like sound generated when you spin across the band and go past the frequency where this computer (man-made) noise is being generated.

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