[TowerTalk] antenna pattern control w/ absorbent material?

[Terry Settergren]

Hi, I can't find many references to this- could an HF antenna, say a vertical, use a shroud of rf-absorbent material to achieve receive (and transmit?) directionality?  What materials, and how close to the element could they be? I have seen tubular rf absorbent materials that appear to be intended to cover a cable, and I keep imagining a rotatable vertical surrounded by a "slotted radome" (pipe), filled with rf absorbent material, with a vertical directional slot exposed. Durable, stealthy, receive directionality, maybe? But I'm ignorant of the effects of the absorbent material near an antenna element.

Regards,
KE5FGX