ARRL Technician Practice Exam

Where must a filter be installed to reduce harmonic emissions from your station?

1. At the power supply

2. Before the receiver

3. Between the transmitter and the antenna

4. After the antenna

The correct answer is: Between the transmitter and the antenna

To effectively reduce harmonic emissions from your station, a filter should be installed between the transmitter and the antenna. Harmonic emissions are unwanted signals that are multiples of the fundamental frequency being transmitted, often resulting from non-linearities in the transmitter itself. When you place a filter at this point, it serves to attenuate these harmonics before they can radiate from the antenna, thus preventing interference with other communication services and keeping your emissions within the legal limits established by regulatory authorities. By contrast, placing a filter at the power supply would not directly address the harmonic emissions traveling to the antenna, as it would only impact the power source rather than the signals being sent. Installing a filter before the receiver could inadvertently block desired signals while failing to mitigate outbound harmonic emissions. Lastly, positioning the filter after the antenna would be ineffective since the harmonics would have already been transmitted into the air, potentially causing interference. Thus, the correct placement to effectively manage and reduce harmful harmonic emissions is indeed between the transmitter and the antenna.