Question E4A07:
Which of the following is an advantage of using an antenna analyzer compared to an SWR bridge?  

Choices:  
A: Antenna analyzers automatically tune your antenna for resonance  
B: Antenna analyzers compute SWR and impedance automatically  
C: Antenna analyzers display a time-varying representation of the modulation envelope  
D: All these choices are correct    

Correct Answer is  B: Antenna analyzers compute SWR and impedance automatically  

To understand the advantage, compare the tools:

- An SWR bridge (SWR meter) shows standing-wave ratio at a single frequency by measuring forward/reflected power; it typically needs a transmitter.
- An antenna analyzer has its own low-power RF source and measures complex impedance over frequency, then computes and displays SWR, resistance, and reactance.

Why the correct answer is correct:
- Antenna analyzers compute SWR and impedance automatically  
  They directly measure the load’s complex impedance, $Z_L = R + jX$, and from that calculate SWR for a chosen $Z_0$ (usually 50 Ω). Many also sweep across frequency to show where $X \approx 0$ (resonance) and minimum SWR without transmitting.

Why the other choices are incorrect:
- Antenna analyzers automatically tune your antenna for resonance  
  Incorrect. They do not tune; they measure. You must adjust the antenna (or use a separate tuner/controller).
- Antenna analyzers display a time-varying representation of the modulation envelope  
  Incorrect. That’s the job of an oscilloscope or modulation monitor, not an antenna analyzer.
- All these choices are correct  
  Incorrect because the two statements above are false.

Useful formulas and tips:
- Reflection coefficient:  
  $$\Gamma = \frac{Z_L - Z_0}{Z_L + Z_0}$$
- SWR from reflection coefficient:  
  $$\text{SWR} = \frac{1 + |\Gamma|}{1 - |\Gamma|}$$
- Return loss (dB):  
  $$\text{RL} = -20 \log_{10} |\Gamma|$$
- Resonance occurs where reactance is near zero:  
  $$X \approx 0 \quad \Rightarrow \quad \text{resonant frequency}$$
- Rule of thumb: SWR ≤ 2:1 is usually acceptable; best match near $R \approx 50\,\Omega$, $X \approx 0\,\Omega$.