[Boatanchors] Grounds, thanks all

[Richard Knoppow]

----- Original Message ----- 
From: "Brian Clarke" <brianclarke01 at optusnet.com.au>
To: "Phil" <ko6bb1 at gmail.com>; "Boatanchor List" 
<boatanchors at mailman.qth.net>
Sent: Wednesday, March 21, 2012 11:48 PM
Subject: Re: [Boatanchors] Grounds, thanks all


> Look Phil,
>
> I think you have a specific mindset here, that you 
> absolutely MUST have a
> ground / Earth system.
>
> It is still not clear to me that you need it for RF 
> purposes at all.
>
> All you continue to describe is a mains safety system.
>
> 73 de Brian, VK2GCE.
>
> On Thursday, March 22, 2012 2:17 PM, Phil said:

      I am not sure I am reading you right so this may not 
be on subject.  An antenna ground system is part of the 
antenna.  The ground acts a mirror for the aerial part and 
determines the radiation pattern.  Some think a symmetrical 
antenna, like a dipole fed with balanced line, is immune and 
does not need a ground; it does because the vertical 
radiation pattern is determined by the ground.  With a poor 
ground the radiation angle tends to be high.  Remember, one 
has essentially _two_ antenna's separated by the distance 
from the antenna to the effective ground.  This is why the 
vertical pattern is affected by antenna height. A vertical 
antenna is also affected although the vertical angle of a 
symmetrical vertical, that is, say, a half-wave dipole 
oriented vertically, would be minimally affected because the 
lower half is essentially the ground.  However, single-ended 
vertical is really a dipole on its side with half being the 
ground reflection.
     In general, ground stakes do not provide an adequate 
ground for antennas. They are mostly for safety grounding 
and lightening protection.  You really need radials, either 
buried or as a ground plane, for a reasonably effective 
antenna ground.  A counterpoise works as well as an buried 
system for most uses.
     All this is covered in many books on antennas although 
some of the newest ones seem to miss it.
     A good antenna ground for HF is fairly large and more 
difficult to install in many areas than the antenna itself. 
If you can't run ground wires then the ground stakes will 
have to do but they never provide a good RF ground.  Even 
the cold water pipes in your house may work better, assuming 
they are metal and reasonably well bonded at the joints.
     Ribbon works better than wire because of the 
distribution of the skin effect.  Skin effect is the result 
of the magnetic field generated within the conductor forcing 
the conducting electrons toward the surface. The flat ribbon 
tends to have more conducting surface for RF than an 
equivalent mass of round wire.  Note that stranded wire has 
no advantage over solid wire of the same diameter because 
the wires are not insulated from each other.  Litz wire, 
which used to be the standard for low frequency coils (like 
IF transformers) has some advantage up to perhaps a 
megahertz but not above.


--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com