I21 - EMC - Basics of electromagnetic compatibility
Quiz
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A common cause of feedback in an amateur installation is from the microphone and cable that pick up RF from the transmitter. The least effective way of preventing this is:
To shield the microphone cables with an earthed sheath
To add ferrite beads to the microphone cables where they enter the radio
To add RF decoupling capacitors between the microphone leads and earth
To use a crystal microphne rather than a dynamic microphone.
To prevent RF entering a power supply the mains wire could be wrapped around a ferrite ring near to the point of entry of the mains lead into the power supply. This is because:
The ferrite and coil act as a transformer to increase the mains frequency
the ferrite and coil have a high impedance at RF frequencies which reduces the flow of RF into the power supply
the ferrite and coil have a low impedance at RF frequencies which reduces the flow of RF into the power
The ferrite and coil act as a transformer to decrease the mains frequency
Which of these would provide the best earthing system for a long wire antenna?
A Connection directly to the mains earth in the house
A series of wires, buried in the ground and connected to the braid of the coax cable
A single copper rod inserted into the ground to which the braid of the coax cable is attached
Five copper rods inserted into the ground to which the braid of the coax cable is attached
Which of these antenna installations will pick up least interference.
A dipole situated well away from the house.
A dipole located in the loft of the house
A dipole located near to an overhead power transmission line
A dipole mounted on the side of a house.
To detect harmonics from a transmitter you could use a general coverage receiver. Which of these is true?
Harmonics would be detected below the frequency of transmission
Harmonics would be detected above the frequency of transmission
Harmonics would be detected above and below the frequency of transmission