Hy End Fed antennas are half-wave antennas that basically work similar to a Zepp or Fuchs antenna. Minimum handling and a relatively high efficiency.
The problem with a lot of portable antennas and antennas in confined spaces is the low efficiency of those antennas. Greatly shortened verticals need a lot of radials for higher efficiency, a dipole would need two anchor points and a heavy feed cable in the centre. Usually this is not possible when going on holiday or with only little space to spare.
In this case a well known antenna concept like the half-wave antenna helps out. Half-wave antennas can be end-fed, because of that the heavy feed cable in the centre is not necessary and the antennas are easier to install. This way only a light fishing rod on the balcony or a suitable tree next to the house is needed. The greater length (λ/2 instead λ/4) increases the efficiency considerably. Single antennas for lower bands use an extension coil.
Another trick by HyEndFed antennas is the transformer (UnUn) with a relatively high transfer ratio of 1:50. Because of that the high impedance of an end-fed half-wave emitter is transformed down to a level with which built-in tuners work well. Sometimes no tuner is needed at all and a counter balance is not necessary either. This is another reason for the antenna design, especially on holiday or with little space. Also, the transformer can cover higher voltage rather easily making HyEndFed antennas capable of higher power.
All power ratings in Watt PEP. All larger antennas have a PL-connector, the QRP and portable version have BNC. There are isolators at balun and at the end of the wire for installation. It may be possible that a guy rope is needed in addition.
Model change 2015
The balun casing of the 'big' multi band antennas (3-band to 5-band, 200W) has a ventilation vent now.
The vent ensures that the internal pressure in the case is equal
to the external pressure and thus prevents water condensation due to
barometric variations (air pressure fluctuations).
The built-in semi-permeable membrane allows gases and water vapor
to diffuse, but prevents intrusion of water and solids like dirt and
insects. This valve must not be removed or sealed.
Review from Funkamateur 1/2013 (PDF, DE, 1.1MB, Reprint with friendly permission from the publisher)