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CCESSORIES
GPS General System Information - V01.03
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hopf
Elektronik GmbH
Nottebohmstr. 41 • D-58511 Lüdenscheid • Tel.: +49 (0)2351 9386-86 • Fax: +49 (0)2351 9386-93 • Internet: http://www.hopf.com • E-Mail: [email protected]
2.3 Lightning Protection
2.3.1 General Information about Lightning Protection
When outdoor antennas are used high interference voltage or current pulses may occur in
the antenna cable during thunderstorms. This may result in damaging or destroying not only
the directly connected radio-controlled clock system but also any other devices connected.
To avoid severe damage and damage-related costs an indirect lightning protection should be
installed between the outdoor antenna and the circuit board of the radio-controlled clock (see
drawing
A15
"Dimensions of Lightning Protector").
2.3.2 Causes of Overloading
Buildings can be protected with the aid of the lightning conductor developed by Benjamin
Franklin. This though does not, however, protect the electronic devices inside from indirect
consequences of lightning.
A flash of lightning is simply an excessive short circuit of two lines with different potentials.
When lightning occurs these two lines are usually two layers of cloud or one layer of cloud
and the earth. Then a current of 1000 to 100000 ampere circulates between the two layers of
cloud or between the earth and the clouds. On unprotected devices connected to open lines
(antenna, antenna cable) this results in the following forms of indirect interference or
destructive influence.
2.3.2.1 Electrostatic Field
The increase of the electrostatic field up to 50 kV/m can be caused by the vicinity of
potential-loaded thunder clouds or by the static charging of the air. Field changes take place
suddenly creating high-frequency, electromagnetic micro-pulses.
2.3.2.2 Increase in the Earth Potential
When lightning strikes into the ground this causes a sudden increase in the earth potential
which depends on the power of the current and on the local specific resistance of the earth.
This overloading is reduced undulatorily through the ground and this causes high voltage-
potential differences in unprotected devices.
2.3.2.3 Electromagnetic Radiation
The flash of lightning may be compared to an antenna of several kilometres length. The
pulse current of several kiloamperes radiates a strong electromagnetic field. This radiation
induces high voltages and currents in "neighbouring" lines (1 to 2 km) which can also cause
overloading in connected devices.