Practical Measurement Scenarios

Putting It All Together — Real Shack Scenarios

Here's how you'd use test equipment to diagnose common amateur radio problems.

Scenario 1: "My SWR is suddenly high on 20m"

Tools needed: Antenna analyser (e.g., NanoVNA)

1. Disconnect the coax from the radio and connect the antenna analyser
2. Sweep 13–15 MHz and look at the SWR curve
3. If SWR is high everywhere: Possible broken feedline or open connection — check connectors and cable
4. If the SWR dip has shifted frequency: Something has changed the antenna (ice, fallen branch, broken element). The analyser shows you where resonance moved to
5. If the impedance shows high R (say 150 Ω): Possible feedline issue — water in the coax can change the impedance

Scenario 2: "Someone reports my signal has splatter"

Tools needed: Spectrum analyser or SDR waterfall, dummy load

1. Connect transmitter to dummy load through a directional coupler or use a loose coupling to the spectrum analyser
2. Transmit into the dummy load while speaking normally
3. Watch the spectrum — your signal should be clean with well-defined edges
4. If you see broad "shoulders" spreading beyond your signal bandwidth: reduce mic gain or drive level — you're overdriving the PA
5. Check that ALC is not being driven excessively

Scenario 3: "I want to check my transmitter's harmonic output"

Tools needed: Spectrum analyser, dummy load, attenuator

1. Connect: Transmitter → Low-pass filter → Dummy load, with a tap or coupler to the spectrum analyser
2. Important: Use an attenuator between the coupler and the spectrum analyser to avoid overloading it!
3. Transmit a carrier and look for signals at 2×, 3×, 4× your fundamental frequency
4. Harmonics should be at least 40-50 dB below the fundamental
5. If they're not, your low-pass filter may be faulty or the wrong cutoff frequency