Which set describes the transmitter protections correctly?

• A. Isolator, Low Pass Filter, Band Pass Cavity
• B. Isolator, High Pass Filter, Band Pass Cavity
• C. Isolator, Low Pass Filter, Noise Filter
• D. Isolator, Low Pass Filter, Band Pass Filter

Answer: (A)

Transmitter protections are about keeping the transmitter safe from reflected power and ensuring emissions stay within the allocated band. An isolator in the output path prevents energy reflected from the antenna from reaching the final amplifier, protecting it from mismatches and high SWR. A low-pass filter then attenuates high-frequency harmonics and out-of-band emissions, helping meet spectral and safety requirements. A band-pass cavity provides sharp, high-Q selectivity for the desired band, strongly rejecting signals outside that band and helping keep power confined to the intended spectrum.

The other options aren’t as effective for protection. A high-pass filter would not effectively suppress the harmonics generated by the transmitter. A noise filter isn’t a standard protective element in the transmitter path. A general band-pass filter lacks the tight selectivity and power-handling characteristics of a band-pass cavity, making it less protective in high-power transmitter hardware.

So, the combination of an isolator, a low-pass filter, and a band-pass cavity best describes transmitter protections.