In this section, question G4C11 was changed slightly, and the answer to question G4C08 was changed slightly.
At some point or another, your amateur radio station will interfere with a radio, television set, or telephone. Sometimes this may be your fault, other times it may be the fault of the device. In either case, you should do everything you can to eliminate this interference.
Public-address (PA) systems and telephones are often targets of interference. Distorted speech is heard from an audio device or telephone if there is interference from a nearby single-sideband phone transmitter. (G4C03) On-and-off humming or clicking is the effect that a nearby CW transmitter may have on an audio device or telephone system. (G4C04)
Fortunately, there are many things you can do to reduce or eliminate the interference. For example, a bypass capacitor might be useful in reducing RF interference to audio-frequency devices. (G4C01) You can also use ferrite beads. Placing a ferrite choke around the cable would reduce RF interference caused by common-mode current on an audio cable. (G4C08)
Proper grounding is also important. One good way to avoid unwanted effects of stray RF energy in an amateur station is to connect all equipment grounds together. (G4C07)
Rather than connecting them in a daisy-chain fashion, you should connect them all to a single point. Connect all ground conductors to a single point to avoid a ground loop. (G4C09) If you receive reports of “hum” on your station’s transmitted signal, this could be a symptom of a ground loop somewhere in your station. (G4C10)
A long ground wire will act more like an antenna at high frequencies than it will at DC or low frequencies. As a result, it is important to keep ground connections as short as possible to prevent high-impedance or resonant ground connections.
One effect that can be caused by a resonant ground connection is high RF voltages on the enclosures of station equipment. (G4C06) If you receive an RF burn when touching your equipment while transmitting on an HF band, assuming the equipment is connected to a ground rod, the ground wire has high impedance on that frequency. (G4C05)
A common complaint of amateur radio operators is electrical noise that seems to be on every band. This may be caused by arcing in a power line transformer or at some other connection. Arcing at a poor electrical connection could be a cause of interference covering a wide range of frequencies. (G4C02)
One thing you might do to reduce or eliminate this interference is use a digital signal processor, or DSP. One function of a digital signal processor in an amateur station is to remove noise from received signals. (G4C11)
You can also use DSPs to eliminate interference from amateur radio signals that are close to the frequency you are operating on. A Digital Signal Processor (DSP) filter can perform automatic notching of interfering carriers. (G4C13)
Many modern amateur radio transceivers have built-in DSPs that operate at IF frequencies, or you can purchase speakers designed for communications use that have audio DSPs. An advantage of a receiver DSP IF filter as compared to an analog filter is that a wide range of filter bandwidths and shapes can be created. (G4C12)
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