Subelement A: VHF-DSC Equipment & Operation— Topic :
Question 10A3
Element 9 (GMDSS Maintainer)A masthead antenna with a base loading coil appears shorted to an ohmmeter check. What might this indicate?
Explanation
An ohmmeter measures DC resistance, not the RF impedance that an antenna presents at its operating frequency. Many antenna designs, especially certain vertical antennas with base loading coils or shunt-fed systems (like some gamma-matched or grounded verticals), are intentionally designed to have a DC short or very low DC resistance between the center conductor and the shield at the feedpoint.
This "DC grounding" can serve a beneficial purpose, providing a path for static electricity to discharge, which helps protect transceivers from lightning strikes or static buildup. Therefore, measuring a short circuit with an ohmmeter can be a normal indication for a properly functioning shunt-fed or DC-grounded antenna system, rather than a fault.
Related Questions
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