Transcript Lightning - Rexburg Hams

Lightning
REXBURG REGION TRAINING
23 JULY 2015
Sources
Three-part QST article
Lightning Protection for the Amateur Radio Station
Ron Block KB2UYT
http://www.arrl.org/lightning-protection
http://www.arrl.org/files/file/Technology/tis/info/pdf/0206056.pdf
http://www.arrl.org/files/file/Technology/tis/info/pdf/0207048.pdf
http://www.arrl.org/files/file/Technology/tis/info/pdf/0208053.pdf
Lightning Characteristics
1. Lots of moist air rising from
ground level to a few
thousand feet
2. Cooler air above with little to
no wind
3. Plenty of sun to heat the air
mass near the ground
As the warm, moist air is heated,
it rises quickly to heights where
the temperature is below
freezing,
Lightning

Within the thundercloud, the
constant collisions among ice
particles driven by the rising air
causes a static charge to build up.

Eventually the static charge
becomes sufficiently large to
cause the electrical breakdown of
the air.
LIGHTNING STRIKE!
Thunder

Several large pulses of energy

> 50,000 °F in 1 microsecond

With no time to expand, creates pressure

Compresses air around the channel

Shock wave faster than sound for about 10 yards

Then an ordinary sound wave  producing thunder!
Generated RF
During a lightning strike your equipment is subjected to several huge impulses
of energy. The majority of the energy is pulsed dc with a substantial amount of
RF energy created by the fast rise time of the pulses. A typical lightning strike
rise time is 1.8 μS. That translates into a radiated RF signal at 139 kHz. Rise times
can vary from a very fast 0.25 μS to a very slow 12 μS, yielding an RF range
from 1 MHz down to 20 kHz. However, the attachment point for a direct
lightning strike has a time as fast as 10 nS.
In addition to the strike pulses, the antennas and feed lines form tuned circuits
that will ring when the pulses hit. This is much like striking a tuning fork in that
ringing is created from the lightning’s pulsed energy.
Current

Average peak current for the first strike is approximately 18 kA.

98% of the strikes fall between 3 kA to 140 kA.

For the second and subsequent impulses, the current will be
about half the initial peak.

The reason that we perceive a lightning strike to flicker is that it
is composed of an average 3 to 4 impulses per lightning strike.
The typical interval between impulses is approximately 50 mS.
What to protect
Transmitting and Receiving Equipment
Antenna Tuner
Linear Amplifier
Terminal Node Controller
Computer
Antenna
Rotor
Transmission Line
Construct a Block Diagram of System
Protect Each I/O Line

Each I/O line is a potential source for lightning strike energy.

The best protection is in series with the equipment.

They limit the amount of lightning strike energy your
equipment will receive.

Let-through energy ratings are in milli- or microjoules.

Select protection devices with the least let-through energy
that meets all the requirements for the connection.
Coaxial Cable Protectors

Not increase system SWR

Induce no signal loss

Broad range of frequencies

Support receive and transmit power levels

Each coax line needs its own protection

Protection mounted to a common plate

Common plate connected to external ground
system
AC Power Protection

Inexpensive

Some depend on safety ground wire

Some use ferrite core inductors

Plastic housings

Printed circuit boards
AC Power Protection – NOT!

Inexpensive

Some depend on safety ground wire

Some use ferrite core inductors

Plastic housings

Printed circuit boards
AC Power Protection

Matches your voltage and current
requirements

Each AC line exiting the circle should
aggregate to a single line
Telephone

Inline device is most effective

Avoid modular connectors.

They are a fragile connector and common amounts of surge
energy are very likely to destroy the connector by welding it or
fusing it open. In addition, there are also issues of flammable
plastic housings, ground wire characteristics, and printed circuit
boards that allow arcs to the equipment side.
Control Circuits

Protection for external devices

Especially tower mounted

Rotor

Shunt-type protection is usually sufficient.
Miscellaneous

Network Connections

Television

Satellite dishes

GPS feed lines
Grounding (in the shack)

All system grounds and protection
devices MUST be connected to a single
“ground” point in the shack.
Ground Bus to External Ground

0.5” wide, #26 AWG (0.0159 inch) copper
strap has less inductance than #4/0 AWG wire

As straight and direct as possible

Width of strap must be wider than total
circumference of coax coming into the
shack.
Outside Ground

A good ground “system”

Not a single ground rod—but a system of interconnected
ground rods

Purpose: Disperse as much lightning energy as possible
before it follows a feed line into the radio system.

The BEST systems can dissipate 90% of the strike energy
into the earth.
Aerial View of Grounding System
Cross-Section of Grounding System
Operating safety
No connection is as good as “no connection”!

No matter how good your lightning protection system is,
you cannot be in contact with the equipment during a
strike. You are the path of least resistance!

Consider a storm warning device.

Leave the shack when the warning sounds.