The EFHW (End Fed Half Wave)..is a popular antenna, and there are plenty of videos on the net showing you how to make one. Recently, new techniques and ferrite materials have come available from Fair Rite that result in significantly greater antenna efficiencies.
I now use a new 43 material cable core that comes in a compact form factor. Fair Rite 2643251002 ( Digi Key)… $8-$10. Quality compensating 2KV capacitors should be used (TDK), and they are also available from Digi Key. They are not expensive.. Do NOT use those inexpensive 15KV caps bought for cheap off of Amazon on the internet, likewise do not use Chinese sourced ferrite materials. The qulity control is poor or non-existant… I know, I purchaed some…. they didn’t work. Probably of some unknown mix.
https://www.digikey.ca/en/products/detail/fair-rite-products-corp/2643251002/8594030
Order TWO… 2643251002 cable cores and some 100pf 2 or 3KV TDK caps, the cost will be around $25, and will arrive post paid by DHL. You can get the wire from Amazon, or an applince repair or motor rewind shop. The insulators are bits of 50mm water pipe with holes drilled in at each end. Black UV treated poly rope or paracord works for the tie downs.. a couple of pulleys could be helpful. The Club (NARA) has been bringing in coax in bulk for resale to club members..check with Devan or Chris.
The EFHW is an extreme off center fed dipole which will work on the multiple harmonics of the fundamental. A 130′ EFHW will work on 80, 40, 20 (yes even 17) 15 and 10 meters. It will sometimes work on 24 as well. A 65′ EFHW will work 40m and up.
So, what’s the attraction? The EFHW a simple, inexpensive and efficient (often over 90%) antenna. As a sloper it’s light and easy to put up. Ideal for NVIS, bug-out, or portable operation where it can be deployed in minutes. The antenna can be also installed as a DX antenna; which is how I use mine. Some fiddling with lengths and experimentation may be needed, but for good DX you need to install it as high as possible. For NVIS ..local rag chews and nets, your 80m EFHW it should be between 25 to 35 feet up, no higher.. an inverted VEE will do. For DX, try to get it up as high as possible.
The EFHW for 80 meters is about 130′ long when using insulated wire, The velocity factor should be taken into account which makes it about 3% shorter. A 5 turn compensating coil is 2 meters from the feed point, but you may not want to put it in.
When winding the auto-transformer, you should NOT use a crossover winding; as often seen on the net. The bifilar (twisted) winding on the primary is optional, it doesn’t seem to make a lot of difference. I don’t have one. If you can, use decent coax; RG8X or RG8/RG213 for lower loss. I use LMR 400. For very short feedline runs, 35′ or so, RG58 is OK.
A Few Additional Notes:
14:2 is 2 turns primary and another 12 secondary for a total of 14.. This makes the transformer a 49:1 auto-transformer. You should use a good quality 2kv or 3kv 100pf cap (TDK) or if you run low power you could even use a silver mica for a compensating capacitor. Your transformer (UnUn) is best wound with #20 or #22 enameled wire… easier on the fingers.
You should NOT need a tuner. This antenna can be erected in any form, it doesn’t need to be in a straight line. It could be an inverted vee or even an ‘L.’. A common mode choke at the antenna is usually not necessary so long as your counterpoise, usually the feedline, does not parallel the radiator in the near field.
I did not put mine in a box or container, but you can if you like. It’s a passive device so there is no urgent need especially for short term portable…I have used this in the driving rain and in the wind of a hurricane… it suffered no damage and the antenna works fine even when wet.
If you can, ground the coax shield at the rig to reduce RX electrostatic noise. Minimum of 35′ of coax (the counterpoise) and the coax should not come away parallel to the antenna primary radiator… this is quite important.
Richard VA7AA/XE1
