Station equipment, antennas, and transmission modes
This section covers the hardware and modes used at a Technician station: transceivers, feed line, SWR, antennas, power supplies, grounding, and the characteristics of FM, SSB, CW, and digital modes. Exam questions test practical equipment choices and the meaning of common specifications.
Feed line, SWR, and station hardware
Coaxial cable for amateur HF/VHF use is typically 50 Ω. Common connectors are PL-259/SO-239, BNC, and N. Feed-line loss rises with frequency and length; RG-58 is thinner and lossier than RG-8. SWR measures impedance match: 1:1 is ideal, 1.5:1 is good, and higher values mean reflected power. An antenna tuner can make the transmitter see a good match, but it does not remove loss in a mismatched feed line. A dummy load lets you test a transmitter without radiating a signal. Power supplies must supply the correct voltage and current; fuses and grounding protect people and equipment.
Antennas
A half-wave dipole is fed at the center and is roughly 468/f(MHz) feet long, with each leg half that. A quarter-wave vertical is about 234/f(MHz) feet and needs a ground plane or radials. A Yagi is directional and has gain in one direction; gain is expressed in dBi relative to an isotropic radiator or dBd relative to a dipole. Polarization is the plane of the electric field; horizontal and vertical antennas should match for best reception. ERP is transmitter power plus antenna gain minus feed-line loss, in dB.
Modes
FM is constant-envelope and common on VHF/UHF repeaters; deviation is typically 5 kHz on 2 m. SSB uses one sideband and no carrier, conserving power and bandwidth; USB is conventional above 10 MHz and LSB below. CW is on-off keyed carrier and is highly effective in weak-signal conditions. Digital modes such as FT8, packet, and DMR encode data; they still require station identification.
Worked example
A 50 W transmitter has 3 dB of feed-line loss and a 6 dBd gain antenna. What is the ERP? Convert to dB: 50 W is about 17 dBW. Net gain is −3 dB + 6 dB = +3 dB, so ERP is 17 + 3 = 20 dBW, or 100 W. In linear terms, 3 dB loss halves 50 W to 25 W, and 6 dB gain multiplies by four to 100 W.
Traps
Do not add dBi and dBd as if they were the same; 0 dBd equals 2.15 dBi. Antenna gain does not create power-it concentrates it. A low SWR does not prove an antenna radiates efficiently; a dummy load has a perfect SWR. Using the wrong sideband or forgetting that FM capture effect can hide weaker stations costs marks.