Question E9C09:
Which of the following describes a G5RV antenna?  

Choices:  
A: A wire antenna center-fed through a specific length of open-wire line connected to a balun and coaxial feed line  
B: A multi-band trap antenna  
C: A phased array antenna consisting of multiple loops  
D: A wide band dipole using shorted coaxial cable for the radiating elements and fed with a 4:1 balun    

Correct Answer is  A: A wire antenna center-fed through a specific length of open-wire line connected to a balun and coaxial feed line  

Correct answer: A — A wire antenna center-fed through a specific length of open-wire line connected to a balun and coaxial feed line

1) Why A is correct
- A classic G5RV is a multiband, center-fed wire antenna whose hallmark is a specific length of balanced open-wire (ladder line or twin-lead) used as a matching section between the dipole and a balun/coax.
- Typical dimensions:
  - Top wire: about 102 ft (31 m)
  - Matching section: about 34 ft (10.4 m) of 300–600 Ω balanced line
  - Then a balun (usually a 1:1 current balun) to 50 Ω coax
- It operates on multiple HF bands (often 80–10 m) with an antenna tuner; the open-wire section provides impedance transformation to make coax feed more practical.

2) Why the others are incorrect
- B: “A multi-band trap antenna”
  - Trap dipoles use resonant L–C traps inserted in the elements to isolate sections by band. A G5RV does not use traps; it uses a specific length of balanced line as a matching section.
- C: “A phased array of multiple loops”
  - The G5RV is a single center-fed wire, not an array, and not loops.
- D: “A wideband dipole using shorted coaxial cable for the radiating elements and fed with a 4:1 balun”
  - That describes designs like the “double bazooka” or coaxial dipole, which use sections of shorted coax as the radiating elements. The G5RV uses conventional wire elements and a separate open-wire matching section; it is not defined by a 4:1 balun.

3) Useful formulas and rules of thumb
- Wavelength conversion: 
  $$\lambda\text{ (ft)} \approx \frac{984}{f\text{ (MHz)}}$$
- Half-wave dipole total length (approximate):
  $$L_{\text{dipole}}\text{ (ft)} \approx \frac{468}{f\text{ (MHz)}}$$
- The G5RV’s 102 ft top is roughly a 3/2-wave on 20 m, and the ~34 ft balanced section serves as an impedance transformer so you can transition to coax (with a balun) and use a tuner for multi-band operation.
- Quarter-wave transformer (general TL rule):
  $$Z_{\text{in}} = \frac{Z_0^2}{Z_L} \quad \text{when } l=\frac{\lambda}{4}$$
  (The G5RV’s matching section length is chosen to provide a useful transformation on several bands; exact behavior depends on line impedance, velocity factor, and frequency.)