End Fed Half Wave Antenna

 

The End Fed Half Wave Antenna (EFHWA) is fed at a voltage node via a parallel resonant circuit against a ‘short counterpoise’, it is a favourite of backpackers and outdoor types.  It can be considered as a half wave dipole that’s end-fed at a voltage node rather than the current node, as is more usual. This is a very handy arrangement for portable QRP work.
EFHWA Link: http://www.aa5tb.com/efha.html

End Fed Half Wave Antenna by AA5TB
http://www.aa5tb.com/efha.html

I suspect that nothing new or radical has happened in the field of radio aerials in a VERY long time, like at least many tens of decades.  Most of the new wonder aerials are really a con.  Choke off the feed-line and then see how good they really are.  Prime among the baddies is the CFA.  It doesn’t really work, at least if you place a choke in the feed-line.  With any real aerial, there should be minimal radiation from the feed system… so a choke should really make no difference at all, but for the CFA it does!  The CFA is not alone, there are others.  The popular G5RV is another design with a radiating feed, deliberately so, but of course G5RV planned it that way.  He wasn’t cheating… merely being a bit devious, to make it multi-band

Lots of stuff to pass on to my fellow radio club members, most of whom are of the  ‘if it’s not expensive, it can’t be any good’ school of thought when it comes to aerials. Nothing of course could be further from the truth!  Aerials are one area where it makes a lot of sense to build our own." Website of GM1SXX - www.observations.biz

Thanks for your email Allan. It's a good idea to point out that an antenna could be pressed into use on odd multiples of its resonant frequency, hence a 3.6MHz antenna for 80m could be useful near the 30 metre, 10.1MHz, band - near to the third harmonic of 3.5 MHz although, as you observe, the radiation pattern may be quite distorted from the traditionally expected dipole pattern and be more petal shaped. The same goes for a 7.1 MHz antenna for 40m being usable on its third harmonic of 21.3 MHz for the 15m band - a 40m dipole being three half waves an the 21 MHz band.

I have not experimented with a full size 80m dipole, but I would guess that it might be useful at 5 times 3.6Mhz in the 18 MHz / 17m band?
The point made about feeding a familiar dipole at the current node rather than the voltage node is obviously very important and, I imagine, sometimes overlooked.
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