[HCARC] Grounding Straps For Safety Ground

[Kerry Sandstrom]

Gary,

An inverted L is essentially a top loaded vertical.  The transmission line 
should be connected between the bottom end of the inverted L and an RF 
ground.  The RF ground should be a large number of conductors covering a 
large area of the ground.  I would guess about a quarter wavelength in 
radius.  It is really no different than a vertical.  Because the top 
horizontal wire of the inverted L acts as top loading/capacitive hat, the 
vertical portion can be shorter than a normal vertical.  I don't think the 
impedance of the inverted L is easy to predict, so you probably need some 
kind of an antenna matching unit at the antenna feed point.  The overall 
efficiency of the antenna depends on how good your RF ground is.  In no case 
is a ground rod an adequate RF ground.

The RF ground has nothing to do with your shack.  The RF ground should be at 
the antenna.  If your antenna is 100 feet away fed by a transmission line 
and if it is a type of antenna that requires an RF ground and your RF ground 
is in your shack, it will make an extremely inefficient antenna system no 
matter how short your RF ground wire is in your shack.

You need a safety ground in your shack.  The safety ground has nothing to do 
with RF.  If your antenna needs an RF ground, you need an RF ground at the 
antenna feed point.  If the feed point is at the base of the tower, then 
that is where you need the RF ground.  You can use any kind of transmission 
line you want.  You just have to match the impedance of the transmission 
line to the impedance of the antenna at the feed point.  If you don't do 
that, then your transmission line will have a higher SWR which isn't in 
itself bad, but it could increase the amount of power you lose in the 
transmission line.

Lightning protection is seldom capable of handling a direct strike because 
of the impedance of the ground wire issues.  Lightning protection is 
generally designed to "bleed off" any charges before they reach the point 
where there is a direct strike.  Charge bleed off is a low frequency event 
which is why the long runs are acceptable.  A direct lightning strike is not 
a low frequency event.  The current has a fast rise time and high frequency 
components.

Are we getting there?

Kerry