End Fed Antennas: Facts or Fable

By Bob²_, W1IS and KC1DSQ 

FACTS

For best results, an End Fed needs a proper counterpoise!

1. An End Fed is just an Off-Center-Fed antenna fed WAY OFF CENTER.
   
2. As with electrical circuits, ALL antennas must have paths to and from a power source.
   
3. If you don’t have a return path on your antenna, RF will find one. Did you know that your body is the return path for the rubber-duck on your HT?
   
4. The outside of the shield of your coax to a 1:1 balun/choke is an excellent End Fed counterpoise. The balun/choke at the proper counterpoise length prevents RF in the shack.
   
5. The proper length for a counterpoise is .05*λ (λ = wavelength of the lowest band). This produces low SWRs on the fundamental and all the harmonic bands.
   
6. The impedance of an antenna goes up as the feed point moves farther from the center.
   
7. The impedance of an Off-Center-Fed antenna fed between 20-33% off Center is about 200 ohms for the fundamental and most of the harmonics.
   
8. The impedance of a single-band EFHW depends on the length of the radiator. For an 80m End Fed: 109ft, impedance is 450 ohms and, for 122.5 ft, impedance is 3200 ohms.
   
9. Multi-band EFHW antennas are usually fed with a 36:1, 1800 ohms or 49:1, 2400 ohms transformer.
   
10. It is possible to make an EFHW antenna to cover from 80m to 6m if losses are well managed.
    
11. An EFHW can be configured as a long wire, inverted V, Inverted L, Vertical or run through trees.
    

Why Use a 36:1 Transformer on a single-band or multiband End FED*

1. Fewer turns have lower leakage reactance requiring a smaller leakage compensation capacitor: 56pF to 82pF on a 36:1 transformer vs. 100 or 150pF on a 64:1 transformer.
   
2. A smaller capacitor reduces the load on the transformer secondary at higher frequencies delivering better performance on 10m and 6m.
   
3. With a proper counterpoise, reactance at the frequency of lowest SWR on the lowest band is ZERO thus aligning minimum SWR with actual resonance. Resistance at resonance is close to 50 Ohms → 1:1 minimum SWR.
   

FABLE

1. End Feds don’t need a counterpoise.
   1. If it is an OCF fed way off center then where is the short end?

Answer: Your Coax feed line, your rig, your body, your house wiring, an unfortunate squirrel, whatever return path the RF finds is your counterpoise.

2. Without a specifically designed counterpoise It may “work” but may not have the SWR or pattern you expected. Without the choke/balun, RF may find a way into your shack with unpleasant consequences.
   

For more information, check our website - OCFMasters.com and click below to purchase our book, “Wire Antennas, 160m to 70cm: Concepts Construction and On the Air” 2^nd edition.

*BalunDesigns.com carries 36:1 transformers and 1:1 baluns with 30dB isolation for End Feds.