A bypass capacitor takes in extra noise or radio frequency interference (RFI) in the system and filters it out.

A diode lets current flow in one direction. If a diode is forward-biased, it's letting current flow, and if it's reverse-biased, it's blocking it. Neither of these things would help remove RF interference.

There is, apparently, such a thing as a bypass inductor, but it's not common, and it's hard to find any information about it, and it doesn't seem like it would help filter out RF interference.

For more info see Wikipedia: Bypass (Decoupling) capacitor, Radio frequency interference (RFI)

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One source of interference could come from arcing at a poor electrical connection. Arcing because of poor wiring or a shorted component will cause fluctuations in the voltage passing that point.

Out of the handbook "Arcing- Any spark or sustained arc creates radio noise over a wide range of frequencies and will interfere with both amateur and consumer reception. [G4C02]"

For more info see Wikipedia: Electrical Arcing

Mnemonic: Sparks fly everywhere

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Hearing distorted speech on an audio device or telephone may occur if there is interference from a nearby single-sideband phone transmitter. Phones and stereos can sometimes pick up extra RF signals from nearby sources, just like your station receiver does, but the speech will be distorted.

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Telephones or audio devices can sometimes pick up interference RF signals from nearby transmission sources. If the interference is coming from a nearby CW transmitter, an on-and-off humming or clicking will be heard, which is a distorted version of the CW transmission. If the nearby interfering station was transmitting in SSB voice, distorted speech would be heard instead.

CW stands for "continuous wave" transmissions. Originally communication was accomplished with a "straight key" and the operator, using "Morse Code" simply used the key to interrupt a continuous transmission into "dits" and "dahs", which explains why there will be clicking from CW interference.

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If you receive an RF burn when touching your equipment while transmitting on an HF band even though the equipment is connected to a ground rod, it may be because the ground wire has high impedance on that frequency. Remember impedance is a resistance to the flow of electrons, if the ground wire has high impedance, then it might have enough "apparent" resistance to make flowing through your equipment or your body a more efficient (lower resistance) path to ground.

Silly hint: if you get a burn on your hand, it will impede your ability to use the hand.

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A resonant ground connection can cause high RF voltages on the enclosures of station equipment.

Even though the equipment is grounded, if the ground wire is long enough it can actually resonate on the frequency you are using to transmit. When this happens, instead of acting to remove extra current, the ground wire gains high impedance, and so blocks the flow of electrons to the ground state. This means your enclosure, equipment or even body can become a more efficient path to ground, and conduct high RF voltages.

Hint: [R]esonant ground = high [R]F

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Connecting all of the ground wires helps keep long individual ground wires from becoming resonant, which causes impedance not allowing extra voltage to escape to ground, but built up causing dangerous RF "hot spots."

For more info see Wikipedia: Ground (electricity)

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RF interference caused by common-mode current on an audio cable can be reduced by placing a ferrite bead around the cable. The ferrite bead, which can also be called a ferrite choke among other names, is used as a device to reduce noise in audio cables because of the high dissipation qualities of the ferrite material.

For more info see Wikipedia: Common-mode interference, Ferrite bead

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A ground loop in your circuits can be avoided by connecting all of the ground conductors to a single point. A ground loop, or extra current path, is usually caused by components that are not designed or wired correctly. Loops can cause noise and interference. Keeping all wiring in direct paths, and especially connecting all of your ground conductors to a single point, help to keep loops from being formed.

For more info see Wikipedia: Ground loops

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If stations that are receiving your communications report back to you that they are hearing a "hum" on your station's transmitted signal, you may have a ground loop somewhere in your station. This unwanted noise caused by picking up distortion from magnetic field voltages or from improper connections can be remedied by connecting all of your ground conductors to a single point.

For more info see Wikipedia: ground loop

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(B). Digital Signal Processors can be used to remove noise from received signals. The processor takes in analog signals and converts them into digital data. The software then can then decode, demodulate, filter or otherwise remove noise, then return the processed signal back to an analog form.

For more info see Wikipedia: Digital Signal Processor, Digital Signal Processing (DSP)

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An advantage of a receiver digital signal processor (DSP) IF (intermediate frequency) filter compared to an analog filter, is that a wide range of filter bandwidths and shapes can be created. The software and processing abilities of the DSP unit make it a very flexible instrument for either filtering or other modifications, signal modulation or other adjustments to the received signal.

For more info see Wikipedia: Digital signal processor, Digital Signal Processing

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(B). A Digital Signal Processor (DSP) filter can perform automatic notching of interfering carriers.

The software flexibility of the DSP makes it a very useful device for modifying or filtering received signals. It can be set to detect and remove nearby interferences by acting as a "notch" filter, to "cut out" the interfering frequencies before returning the "cleaned" signal back to analog form for listening.

For more info see Wikipedia: Digital Signal Processor, Digital Signal Processing

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