A full-sized 80-meter antenna usually requires a large amount of space, making it difficult for many amateur radio operators to install at home. A shortened End-Fed Half Wave (EFHW) antenna provides a practical alternative by offering multi-band HF coverage in a compact layout.
This shortened EFHW antenna covers 80m through 10m using a 49:1 transformer, a 110µH loading coil, and a carefully tuned wire length. The design works well for backyard installations, portable operations, and limited-space amateur radio setups.
What Is a Shortened EFHW Antenna?
An End-Fed Half Wave antenna is a single-wire antenna fed from one end instead of the center. Because the feedpoint impedance is extremely high, a matching transformer is used to convert the impedance closer to 50 ohms for standard coaxial cable and HF transceivers.
The shortened version uses a loading coil to electrically lengthen the antenna for 80-meter operation while maintaining performance on higher HF bands.
This antenna design includes:
- Approximately 67 feet of wire before the loading coil
- A 110µH loading coil
- Approximately 8 feet of wire after the loading coil
- A 49:1 UNUN transformer
- An RF choke near the feedpoint
The total antenna length is approximately 75 feet, making it much shorter than a full-size 80m dipole.
Antenna Layout and Installation
The antenna is commonly installed as a sloper or inverted-L configuration using PVC or fiberglass support masts.
Recommended Dimensions
- Main radiator wire: 67 feet
- Wire after loading coil: 8 feet
- Total wire length: approximately 75 feet
- Recommended apex height: around 8 meters
The loading coil is placed near the far end of the antenna, leaving a short wire section after the coil. Proper coil placement is important for correct resonance and multi-band operation.
This antenna can easily fit into small backyards where traditional 80m antennas are impossible to install.
The 49:1 Transformer (UNUN)
An EFHW antenna normally presents a feedpoint impedance between 2000 and 5000 ohms. A 49:1 transformer converts this impedance to a level suitable for 50-ohm coaxial cable.
Common ferrite cores used include:
A typical winding arrangement uses:
- Two bifilar primary turns
- Fourteen secondary turns
Many builders also add a 100pF high-voltage capacitor across the transformer input to improve SWR on the higher HF bands.
How the 110µH Loading Coil Works
The loading coil is the key component that allows this antenna to operate effectively on 80 meters without requiring a full-size wire length.
The coil serves two functions:
- Electrically lengthens the antenna for 80m
- Acts as an RF choke on higher frequencies
XL=2πfLX_L = 2\pi fL
At 7MHz, the 110µH loading coil produces approximately:
XL=2π(7×106)(110×10−6)≈4.8 kΩX_L = 2\pi (7\times10^6)(110\times10^{-6}) \approx 4.8\,k\Omega
This high reactance limits RF current flowing into the final wire section on higher bands while still supporting resonance on 80 meters.
Loading Coil Construction Details
The loading coil can be built using enamelled copper wire wound on PVC pipe.
Typical Coil Specifications
- Inductance: 110µH
- Wire size: 1mm enamelled copper wire (approximately AWG #18)
- Coil former: PVC pipe
- Coil position: near the end of the antenna
Depending on the PVC pipe diameter, builders may use different winding counts:
- Approximately 76 turns on 40mm PVC pipe
- Approximately 260 turns on 19mm PVC tubing
Both methods can achieve approximately 110µH inductance.
Coil Building Tips
For reliable performance:
- Secure the starting wire with a solder lug or bolt
- Keep turns evenly spaced
- Tape the winding while building
- Waterproof the finished coil using electrical tape or heat shrink
- Mount the coil securely to reduce movement in wind
A neat winding layout improves consistency and long-term durability.
Why the RF Choke Is Important
An RF choke helps prevent RF current from traveling back along the coax shield.
Without a choke, the coax can become part of the antenna system and create several problems:
- RF feedback in the radio shack
- Increased noise pickup
- Unstable SWR
- Distorted radiation patterns
A common RF choke design uses:
- 10 turns of RG213 coax on a 4-inch former
- Or several turns of coax through an FT240-43 ferrite core
The choke is normally installed about one meter from the feedpoint transformer.
Tuning the Shortened EFHW Antenna
Tuning is usually performed in two stages.
Step 1: Tune the Main Wire
Adjust the 67-foot wire section before the loading coil until resonance falls near 7.1MHz for the 40-meter band.
Step 2: Tune the Final Wire Section
After tuning 40m, adjust the 8-foot wire section after the loading coil for proper 80-meter resonance. Small changes in wire length can significantly affect SWR, so trim the wire gradually.
Performance
This shortened EFHW antenna delivers good multi-band performance considering its compact size.
Typical performance includes:
- Low SWR on 80m and 40m
- Below 3:1 SWR on 20m, 15m, and 10m
- Approximately 300kHz bandwidth on 80m
- Good performance for portable and backyard HF operation
Performance on 80m may not equal a full-sized dipole, but the antenna still performs well for regional communication, portable operation, and everyday amateur radio use. The shortened EFHW antenna is an excellent solution for amateur radio operators who need an effective multi-band HF antenna in limited space.
By combining a 49:1 transformer, 110µH loading coil, RF choke, and carefully tuned wire lengths, this design provides reliable coverage from 80m through 10m while remaining compact and easy to install. For operators with small backyards, portable stations, or HOA restrictions, this shortened EFHW antenna offers a practical and efficient HF antenna solution.
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