Choose the right meter or scope for each station measurement and explain how a two-tone test and antenna analyzer work.
Syllabus: Tests and test equipment
Practise the 13 pool questions for this group. Answers are shuffled, and every one comes with a one-line "why".
An oscilloscope has vertical and horizontal channel amplifiers: signal strength up, time across. Unlike a voltmeter it shows complex waveforms, so it's the tool for a CW keying waveform or the RF envelope of a transmitter, fed from an attenuated sample of the RF output.
A two-tone test sends two non-harmonically-related audio tones into an SSB transmitter. The envelope should be a clean beat pattern. Flat tops mean poor linearity.
RememberScope shows the shape. Two-tone test checks linearity.
Connected across a circuit, a voltmeter's input resistance forms a divider with the circuit's own resistance. High input impedance keeps loading small, so the reading stays true.
| Digital multimeter | Analog multimeter | |
|---|---|---|
| Strength | Higher precision | Moving needle shows trends |
| Best for | exact readings | adjusting for a maximum or minimum (peaking, nulling) |
RememberHigh input impedance, less loading. Needle for peaking, digits for precision.
A directional wattmeter sits in the line with a running transmitter and reads forward and reflected power, so you get SWR. An antenna analyzer makes its own signal, so connect only the antenna and feed line.
| Analyzer measures | Not an analyzer job |
|---|---|
| SWR, impedance (including coax impedance) | transmitter power output |
| antenna gain or front-to-back |
Strong signals from nearby transmitters get into the analyzer and interfere with SWR readings.
RememberWattmeter: SWR with a transmitter. Analyzer: antenna and line only, no transmitter.