Is this the secret of success of Coco made of corrugated sheathed Andrew Heliax coax?
When Coco elements are cut to length = VF x 1/2 wavelength:
The phasing element’s (core wire):
- Physical length = VF x 1/2 wavelength
- Electrical length = 1/2 wavelength - OK, optimum.
The radiating element’s (outer surface of the shield):
Physical length = VF x 1/2 wavelength
Electrical length = Physical length = VF x 1/2 wavelength - NOT OK, optimum is 1/2 wavelength.
This can be overcome by using air insulated elements (vf = 1).
Incidently in a currogated sheathed coax, the current on the sheath has to travel along the curved surface of sheath which is a longer path than if the sheath was plain, compensatig for shortfall caused by cutting short by a factor of VF.
