VHF antenna is vertical antenna with the length of approximately 1 m. VHF antenna is placed on a position as high as possible. The connection between the VHF radio and VHF antenna is made by coaxial cable.

antenna cable
Coaxial cable
A: outer plastic sheath
B: copper screen
C: inner dielectric insulator
D: copper core

This coaxial cable will have an impedance (resistance for alternating current AC) of 50 Ω (Ohm). This impedance will be the same on the VHF radio antenna cable connector as well as on the cable connector on the antenna. When this connection is not 50 Ω there will be not only radiated power in the cable but also some reflected power. When the level of reflected power is too high this will reduce your emission of radio signal and this will lead to a shorter range of maximum reach of your signal. It could also damage your VHF radio when the reflection is very high for a longer period of transmission. This above mentioned problem will also cause a loss of signal strength (in the antenna cable) of received signals.

The change in the impedance of the antenna cable could be caused by water in the antenna cable. When the cable is damaged on the outside (outer plastic sheath) water could enter the cable (in the copper screen). This water will change the impedance of the cable and this will lead to a reflection of power. Also the cable connection to the antenna could cause this problem (water entering the antenna cable). This connection should be made waterproof; this could be done by using vulcanizing tape.
Last modified: Saturday, 25 April 2020, 7:50 PM