[AMRadio] Tower Construction


Stevan A. White w5saw at pathwayz.com
Tue Jun 13 01:09:23 EDT 2006


I see that I left out a sentence.  "Lay the appropriate length radials in
the ground for your RF ground return and bond them to the ring."  I was
thinking it but failed to type it in.

Gary makes some good points about high impedance paths for lightning.  I
agree that lightning will not make several sharp turns through all the
connections I described.  Radials will help dissipate lightning and static
charges but you can only connect several radials to each ground rod without
making somewhat of a mess.  The ring affords you a connection path for many
more radials which will provide a better RF ground return if that's your
goal.  Many standard broadcast AM towers have ground radials configured this
way.

The bottom line is, there's a lot to consider when designing and building a
ground system.  Do a little research and don't rush into it.  Figure out
what will best serve you for your installation and do what you can afford.

That's all from me for now.  Best wishes!

Best Regards,
Steve White, W5SAW
SW Commercial Electronics


-----Original Message-----
From: Gary Schafer [mailto:garyschafer at comcast.net] 
Sent: Monday, June 12, 2006 9:26 PM
To: 'Stevan A. White'; 'Ed Swynar'; 'Discussion of AM Radio'
Subject: RE: [AMRadio] Tower Construction




>This affords you the
> opportunity
> to bond the tower, rebar, AND several copper clad ground rods together
>for  the best possible DC ground for your tower.  If you want an RF 
>ground  return  for your installation, install a heavy duty copper ring 
>and bond it to the  ground rods.
> Best Regards,
> Steve White, W5SAW
> SW Commercial Electronics

A good lightning ground is also a good RF ground. This means several radials
should be installed along with the ground rods.

A ring connecting ground rods around the tower does nothing for a lightning
ground. The lowest impedance is in a straight line out away from the tower.
A sharp turn at the junction of the "ring" to get over to the next ground
rod in the "ring" looks like a high impedance path to the lightning as the
sharp turn has considerable inductance. Also the other ground rods in the
ring are already at the same potential as they are connected directly to the
tower. The lightning will be carried out away from the tower in all
directions. There will be no current carried by the ring connection so it is
a waste of wire. The ground system would be better served by using that wire
for another radial.

73
Gary  K4FMX






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