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Bruce in Alaska wrote in news:bruceg-
:
Ground is not Ground, the world around....RF Grounds are different
than other Grounds, and should not be confused with these other
Grounds.
1/4 wavelength down the wire from "ground", a voltage reference to which
other points are measured, is an OPEN. At this point, induced voltage in
the "ground wire" or "shield" is at maximum, and can be high enough to kill
around high powered transmitters. As you approach 1/2 wavelength from
"ground", once again you find a null of voltage. Again at 3/4 wavelength
from "ground", we once again find a maximum voltage lobe that may burn you.
We don't HAVE to connect anything in RF to "ground ground", Mother Earth,
to get a "ground". If we lay out a piece of wire and keep the end from
touching anything conductive, usually by putting an insulator there or
using tubing at higher frequencies which requires no insulator and support
structures to hold it up...we get an "artificial ground". Look at any
common CB "ground plane" antenna and note the "radials" sticking out from
the base where the coaxial shield is connected to these "radials" that are
1/4 wavelength long. The end of the radials is open, at least a very high
impedance in common air. 1/4 wavelength back from that "open" is the
artificial ground, where the coax shield is connected. This point performs
at some high altitude just as if the shield were connected to "ground
ground", as far as the RF is concerned (but NOT the lightning!). A 1/4
wavelength "sleeve" (beer cans with the ends cut out welded together end to
end work great for hams), with the coax going up inside the sleeve but not
touching its open end, also makes an artificial ground 1/4 wavelength away
from the open end.
--
Larry
This jerk called my cellphone and was nasty.
Continental Warranty -- MCG Enterprises -- Mepco-
24955 Pacific Coast HWY Suite C303
Malibu California 90265
888-244-0925
Fax: 310-456-8844
Email:
Read about them he
http://www.ripoffreport.com/view.asp...3&view=printer
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