[TowerTalk] RF on stainless steel
RedHaines at centurytel.net
Mon Jun 12 16:02:35 EDT 2006
Any of the stainless steel alloys are suitable for grounding an antenna
element to the boom to prevent arcing. Moderately high impedance won't
prevent them from limiting the voltage difference between the element
and the boom to less than the voltage needed to initiate an arc or even
a corona discharge. Half the energy of a lightning strike is below
one MHz and half is at higher frequency.
However, the resistance of some stainless steel alloys, especially at
the higher RF frequencies, may cause some loss when the objective is to
carry part of the antenna current. While skin effect won't prevent a SS
strap from effectively grounding the element to the boom as far as
lightning is concerned, it will cause some loss of 160 meter and 80
meter signals (or higher).
Skin effect depends upon frequency and the permeability of the metal.
Higher frequency limits the depth of current and increases resistance.
Higher permeability also limits the depth of current and increases
Some stainless steel alloys are non-magnetic and thus their skin effect
is less pronounced than that of the magnetic alloys.
The skin effect is much more serious in conductors intended to limit
lightning potential for the purposes of protecting equipment in the ham
station, where an ideal is to approach zero impedance. While any
stainless steel strap may prevent arcing, some are definitely undesired
in applications where their purpose is to protect equipment.
73 de WOØW
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