Protecting Your Shack From Lightning (as best you can) Hap Griffin WZ4O

Point of reference – 0 volts potential Concept of “Ground”: Point of reference – 0 volts potential Circuit returns Actual “Earth” ground For lightning, actual Earth is the point of reference

Types of Grounding: Safety Grounding (NEC) – 60 Hz RF Grounding – Frequencies in Use Lightning Protection (Mitigation) – DC to RF If #3 is implemented properly and fully, #’s 1 and 2 will likely be covered.

Surge Protection in Shack: Don’t scrimp here – avoid cheap units Look for protection capacity in Joules: higher = better Metal case with ground screw Don’t rely on “Protected” light on cheap units Rated at 3840 Joules Rated at 300 Joules

UPS / Surge Protection in Shack: Combines UPS / AVR and Surge Protection Rated at 1200 watts Rated at 2200 Joules

Multiple Ground Points vs Single Point Ground

In a physically distributed multiple ground system, tie EVERY conducting object together with LOW IMPEDANCE conductors to minimize voltage differences during a lightning strike (i.e fences, light posts, tower, etc).

Ufer Ground

Ufer Ground

Bring all cables to BOTTOM of tower and provide lightning path to ground AT THAT point

Bring all cables into building through a bulkhead grounded plate Use coaxial and multi-line surge protectors AT THAT POINT (NOT in the shack)

PolyPhaser – Block DC, internal gas tube Alpha Delta – Pass DC, replaceable gas tube

Characteristics of Grounding Conductors: Since we are dealing with lightning currents that have large RF components, we must think about LOW RF IMPEDANCE, not just low DC resistance.

Effects of Length of Conductors

Ground wire = #6 (4.11 mm diameter) Ground Wire Length = 20 feet Example: Frequency = 7 MHz Ground wire = #6 (4.11 mm diameter) Ground Wire Length = 20 feet From online calculators: The inductance of the ground wire (assuming it is straight) = 9490 nH Inductive reactance at 7 MHz = 417 ohms If ground wire approaches ¼ wavelength long, it is effectively not there at all. ¼ Wavelength = 80 mtrs – 60 Feet 40 mtrs – 40 Feet 20 mtrs – 20 Feet 15 mtrs – 11 feet 10 mtrs – 8 Feet

“Skin Effect” of Conductors

Use Conductors With Lots of Surface Area Use Gentle Turns

“Cadwelding”

Use Coax Switches That Ground Inputs Not In Use and That Have a Ground All Inputs Position = BAD

Summary: Think in terms of propagation time Think in terms of RF – low impedance paths to ground rather than just low resistance Think of your entire facility – not just the shack Damage comes from differences in potential (voltage) – tie EVERYTHING together with low impedance bonds

Questions?