Where is a low pass filter usually connected in an HF station?

A low pass filter is typically connected closest to the antenna in an HF station to effectively eliminate unwanted high-frequency signals that may interfere with your transmission and to ensure that only the desired low-frequency signals are transmitted. This placement helps in minimizing spurious emissions and harmonics that can degrade the overall performance of the station and may cause interference to other services.

By placing the low pass filter at the antenna, it can reduce the risk of these unwanted signals radiating from the feedline as well, thus promoting cleaner transmission characteristics. Additionally, positioning the filter here helps protect the receiver from out-of-band noise and signals that could be present on the line, improving overall reception quality.

While it can be important to filter signals at various points in an HF station, connecting the low pass filter closest to the antenna aligns well with the objective of maintaining signal integrity and adhering to regulatory requirements regarding out-of-band emissions.