Subelement B: MF-HF-DSC-SITOR (NBDP) Equip. & Ops— Topic :
Question 12B2
Element 9 (GMDSS Maintainer)What is the function of the “TUNE” button on a MF/HF transceiver?
Explanation
The "TUNE" button on an MF/HF transceiver activates a process to tune the antenna system. Its primary function is to adjust the impedance of the antenna and feedline, often through an internal or external antenna tuner (ATU), to match the 50-ohm output impedance of the transceiver's final amplifier. This impedance matching minimizes Standing Wave Ratio (SWR) on the feedline, ensuring maximum power transfer from the transmitter to the antenna and protecting the transmitter's final amplifier from damage due to reflected power. This is critical on MF/HF bands where antenna impedance varies significantly with frequency.
Options A and B are incorrect; tuning in a channel or receiver frequency is accomplished via the main tuning dial or keypad (VFO), not a "TUNE" button. Option D is incorrect; the AF (audio frequency) amplifier operates at audio frequencies and does not require RF tuning.
Related Questions
11B6 What are the assigned frequencies for VOICE and SITOR (NBDP) follow on communications?12B1 What is the purpose of the “R.I.T.“ control on a MF/HF transceiver?12B3 What is the purpose of the “ENTER” function.12B4 What mode is a MF/HF transceiver operating in when “TLX” displayed?12B5 Reducing the “RF Gain” control on an MF/HF transceiver has what effect?