[TenTec] On Grounding

[Robert & Linda McGraw K4TAX]

This message started with other Tentec subject lines but due to the subject
matter and the fact it's summer (thunderstorm season) here in the US, I
thought I'd pass along a few ideas and facts and try to dispel some
incorrect notions regarding grounding.

Today most ham stations do not need a RF ground.  Shocking to read isn't it!
Well it's true.  Ask, does your antenna system require a ground to operate?
If you use a vertical, an inverted L or a long wire or a sloper or other
unbalanced configuration then with out question your antenna does require a
ground to operate satisfactorly.  On the other hand, if you use a coax fed
beam, a coax fed dipole, a balanced fed loop or a balanced fed dipole
(resonant or non-resonate) then the antenna system does not need a ground.
Any of these will work just fine even in outer space and certainly there is
no place to drive a ground rod there.  Oh my!

Then why do we jump through hoops to put in a ground system?  Simple,
lightning protection.  On this topic, one thing to remember is the fact that
all driven grounds must be bonded together in order to be effective during a
nearby lightning strike.  The NEC electrical code requires it.  And it isn't
safe if its not done.  That means the tower ground, the TV antenna ground,
the telephone ground, the well pump and anything else that could be
considered as needing ground for lightning protection.  And of course the
lightning rods on the house.  You do have them don't you?  Or is your tower
the lightning rod?   None of these items actually require any form of RF
ground.

Now we must decide do we need a RF ground or a lightning ground.  We
generally believe that we must connect everything together in all sorts of
helter skelter ways and schemes producing multiple paths for current flows.
In days gone by, transmitters and antennas did require a RF ground to
operate satisfactorily but their output circuits were vastly different from
todays radios.  Today, the most effective method is to connect a reasonably
large, low resistance, low inductance wire from one piece of station
equipment to another.  In the simplest terms, tuner ground connected to
amplifier ground, amplifier ground conected to tranceiver ground and
tranceiver ground connected to the power supply ground.  At this point then
where is ground connected?  For safety reasons and according to the NEC, the
3rd pin of the AC line completes the requuirements.  I use #10 AWG stranded
with #30 wire marine cable and apply crimp on connectors and then solder the
connectors too.  This makes for a very low R connection, yet it's very
flexable and easy to work with and  move equipment around as needed.

For lightning protection all feedlines, being coax or balanced, all rotor
lines and remote antenna switching control lines should be protected by an
approprate device (I'll not mention brands) at the point they enter the
building.  The antenna supporting structure must be grounded at its base and
this ground must be connected to the AC mains ground by some hard bonding
technique.  Failure to do this will (repeat WILL) produce a step voltage
between the two during a nearby lightning strike.  The result is that
current will flow between the two and usually the radio equipment is in the
current path and is the first to smoke.

If you have applied an external ground to eliminate TVI, BCI or telephone
interference then the topic of discussion should turn another direction.  In
most cases there's problems with the relationship between the antenna and
the device being offended with.  (pardon the grammar)

In most cases we go overboard to provide what we believe to be a good ground
system when indeed it is not needed and worse, it is often applied
incorrectly.

I will directly respond to all e-mail questions if you would like more
dialogue on the topic.

73
Bob, K4TAX