[TowerTalk] Lightning Ground & RF Ground

[Gary Schafer]

> -----Original Message-----
> From: towertalk-bounces at contesting.com [mailto:towertalk-
> bounces at contesting.com] On Behalf Of Phil Camera
> Sent: Thursday, January 04, 2007 6:32 PM
> To: towertalk at contesting.com
> Subject: [TowerTalk] Lightning Ground & RF Ground
> 
> A well designed lightning ground will also make an excellent
> RF ground for a vertical antenna. If it will not serve as an RF ground
> then
> it is not an adequate lightning ground either.
> 
> 
> 
> No not really.  They are two totally different animals and neither will be
> a
> substitute for the other.

No they are NOT two totally different things! Please note that I did NOT say
that a good RF ground (such as elevated radials) would necessarily make a
good lightning ground.

> 
> With lightning grounding, we are looking for a low impedance/low
> resistance path to ground
> (at multiple spots) and are talking about high current and voltages.
> 
> For RF grounding, we are looking for the same but for low currents for our
> antenna to work
> against.

A good RF ground has the same requirements. It must also be very a very low
impedance and be able to handle high currents. If it can't handle high
currents then its resistance is too high to make a good RF ground. In an RF
system the peak currents will not be as high but they will be constant.

> 
> A super counterpoise radial system with lots of radial wires of small
> diameter located near the surface of ground
> will not do diddly for dissipating a lightning strike.  And likewise 50 ft
> per tower leg of grounding wire connected to
> ground rods every 2X the rods' heights, will not form a proper RF radial
> field.

Note again that I did NOT say that a good RF ground was necessarily a good
lightning ground. I said a good lightning ground WAS a good RF ground.

3 radials with ground rods installed does not make a good lightning ground
either. It is a minimal lightning ground.

> 
> Having both and connecting them together, they always are connected
> together since each connects to the tower,
> won't hurt, but they are really two different systems for two different
> purposes.

They can be the same system. If you have an excellent lightning ground then
you also have a very good RF ground system. A good part of lightning is RF
and must be dealt with in the same way.

A typical AM broadcast ground system is both a good lightning ground and a
good RF ground system.

73
Gary K4FMX

> 
> Phil  KB9CRY
> 
> (who's been laying low this time around on the bimonthly lightning
> discussion!)
> 
> 
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