Designing a centerloaded vertical  for HF applications is a matter of sound engineering practices, common sense and obeying the laws of physics.
The principle of creating an efficient vertical radiator by using inductive center loading an capacitive top loading  are well known amongst designers of these antennas.
In order get an adequate performance on the lower frequencies some guiding principles have to be taken into account:

1: center loading
2: reduction of coil losses
3: use of capacative top loading

Charlie Gyenes, owner of HiQ Antennas and holder of a number of patents has exactly implemented these principles in the design of the HiQ Antenna range.
With his professional background in the aerospace industry and by application of sound engineering practices he made a professional antenna system available for mobile , maritime and base applications. Clearly, short verticals have all sorts of drawbacks compared to full size antennas, but in many circumstances the short vertical is the only option. There is NO magic here only common sense. Way to go is to optimize the design and minimize losses in order to achieve the best results. 

1: Large loading coil diameter and proper wire spacing in order to obtain  a high Q factor
2: Adequate coil wire diameter  in order to minimize losses
3: Silver or gold plated contactor components
4: two point suspension of contactor
5: No moving parts outside
6: No mechanical stresses on the contactor

There are NO other designs  currently available in the market offering these features and performance. 

For a more detailed and in depth view please check www.hiqantennas.com..