Transmitters, Receivers, Measurements and Interference Suppression
What you must know
Transmitter topics: oscillator stability, frequency synthesis with PLL, buffer and driver stages, PA classes (A, AB, B, C), harmonic and spurious emission limits, output filtering, keying and SSB generation, and the causes of splatter and key clicks. Receiver topics: sensitivity, selectivity, dynamic range, intermodulation, blocking, image frequency, mixer principles, AGC, and the superheterodyne architecture with intermediate frequency. Measurement: power meters, dummy loads, SWR bridges, oscilloscopes, frequency counters, and the difference between peak envelope power and average power. Interference suppression: ferrite chokes, shielding, grounding, common-mode currents, filters, and the obligation to investigate and eliminate interference caused by your station.
Typical traps
Confusing sensitivity with selectivity, or image frequency with the intermediate frequency. Questions about PEP versus average power for SSB (PEP is roughly 2–4 times average for speech). Over-driving an amplifier raises splatter and harmonics rather than useful output. Also remember that a dummy load must match the transmitter and handle the power; measuring with an antenna connected is not a substitution.
Worked example / rule of thumb
If the intermediate frequency is 9 MHz and the receiver tunes 14.2 MHz, the image lies at 14.2 ± 2·9 MHz, i.e. about 32.2 MHz or 3.8 MHz depending on mixing; a preselector filter suppresses it. Rule of thumb for interference: fix the source before adding filters - check common-mode current with a clip-on ferrite on the coax, then improve station grounding.
Exam technique
When asked for the "first" or "most effective" measure, prefer the one that removes the cause (shielding, grounding, filtering at the source) over one that merely masks the symptom.