Antenna Systems, Transmitter Operation and Installation Practices
This domain tests whether you can reason about the whole chain from transmitter output to radiated field: feedline loss, impedance match, antenna gain and polarization, plus the installation practices that keep that chain safe and legal.
Feedlines and matching
Systems are standardized at 50 ohms. Voltage standing wave ratio, return loss and mismatch loss describe the same mismatch from different angles. Feedline loss is quoted in dB per 100 m and rises with frequency and with moisture in connectors. A poor match reflects power back to the transmitter, where it becomes heat and can damage the final stage.
Antenna characteristics
Gain in dBd references a dipole and gain in dBi references an isotropic radiator, differing by 2.15 dB. Beamwidth, front-to-back ratio, polarization and height above ground all change coverage. System gain is arithmetic: transmitter power minus feedline loss plus antenna gain equals ERP.
Transmitter operation
Know rated output versus actual, continuous versus peak envelope power, duty cycle, frequency stability, harmonic and spurious suppression, occupied bandwidth, cooling and keying characteristics. Limits in a standard are usually stated as average power over a defined interval, never as peak envelope power.
Installation practices
Work to the Canadian Electrical Code, bond mast and equipment to a single ground point, fit an antenna discharge unit, keep antennas clear of power lines, provide drip loops and strain relief, and weatherproof every outdoor connection.
Worked example
A transmitter shows 100 W forward and 4 W reflected. The reflection coefficient is the square root of 4/100, or 0.2, so VSWR = 1.2/0.8 = 1.5:1, return loss is 20log(0.2) = 14 dB, and mismatch loss is only 0.18 dB, leaving about 96 W. With 3 dB of feedline loss, 48 W reaches the antenna. Adding 6 dBd gain gives ERP of about 191 W, or 22.8 dBW.
Traps that cost marks
Measuring VSWR at the radio rather than the antenna, where feedline loss flatters a bad antenna; assuming 1:1 proves the antenna radiates; mixing dBd and dBi; and quoting peak envelope power against an average-power limit.