Signals and Emissions
Modulation and bandwidth
Know the difference between AM, FM, SSB, and CW. AM has a carrier and two sidebands; SSB suppresses the carrier and one sideband, saving power and bandwidth. FM has constant amplitude and varying frequency; its bandwidth depends on deviation and modulation frequency (Carson's rule approximates it). Know that CW is the narrowest common mode and that digital modes vary widely in bandwidth.
Emission designators and spurious signals
Know that an emission designator describes bandwidth and modulation (for example, a designator starting with a number gives bandwidth in Hz followed by letters for modulation). Know that harmonics are multiples of the fundamental and that spurious emissions must be suppressed. Know that intermodulation products arise when two signals mix in a nonlinear stage and can cause interference.
Keying and distortion
Know that key clicks come from too-fast rise and fall times, and that splatter comes from overmodulation or excessive audio. ALC (automatic level control) helps prevent overdrive. Know that SSB requires linear amplification to avoid distortion.
Worked example
A transmitter on 7.030 MHz produces a signal at 14.060 MHz. That is the second harmonic and should be suppressed by filtering. If two strong signals at 7.030 and 7.040 MHz produce a product at 7.050 MHz, that is a third-order intermodulation product (2f1 − f2).
Common traps
Confusing harmonics (multiples of one signal) with intermodulation (products of two or more signals). Assuming FM bandwidth equals deviation alone. Forgetting that SSB needs linear amplifiers.