The EFHW..is a
popular antenna. There are plenty of details on the net on how to make
one, but there are some new techniques and materials that result in
significantly greater efficiencies.
I now use a new 43 material cable core, Fair Rite 2643251002 in new
compact form factor ( Digi Key) and they are very inexpensive… $8-$10.
The EFHW is really 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 17) 15 and 10 meters. They will sometimes work on 24 as well. A 65′ EFHW will work 40 and up.
So, what’s the attraction? It’s a simple, inexpensive and efficient (over 90%) antenna. As a sloper it’s light,and easy to put up, ideal for NVIS portable operation where it can be deployed in minutes.
Or it can be installed as a DX antenna, which is how I use mine. Some fiddling with lengths and experimentation may be needed
A few notes:
The EFHW for 80 is 130′ long when using insulated wire (the velocity factor makes it 3% shorter)The compensating coil is 2 meters from the feed point…you may not want to put it in.You do NOT use a crossover winding… it is unnecessary.The bifilar winding on the primary is optional… doesn’t seem to make a lot of difference… I don’t have one.14:2 is 2 turns primary and another 12 secondary for a total of 14.. This makes it a 49:1 autotransformer.Use a good quality 100pf cap (TDK) or if low power you could even use a silver mica. 100pf @ 3KVYou should NOT need a tuner… especially on 40 and 20The antenna can be in any form… it doesn’t need to be a straight line… it could be an inverted vee or L. You should not need a common mode choke at the antenna… your feedline is the counterpoise if you can, ground the coax shield at the rig… sometimes reduces RX static noise. Minimum of 35′ of coax (it’s the counterpoise) and the coax should not come away parallel to the antenna radiator.Use decent coax, RG8X or RG8 for lower loss RG213 is OK too. I use LMR 400
It can be made specifically with a single band in mind… where the vswr is perfect or close on say 3730 khz
I did not put mine in a box or container…It’s a passive device so there is no need especially for short term portable…I used this in the driving rain and wind of a hurricane… it suffered no damage and works fine when wet.
73 Richard VA7AA/XE1