Magnetic antennas¶

Either ferrite rod antennas or Loop Antennas may be used. A magnetic antenna does not need to be mounted high since the magnetic field is not easily attenuated. They must be a minimum of several meters from other electrical installations - in the garden just above the ground, attic, or on a balcony is ok.

We normally use 2 rods, but BLUE allows for an extra - which could be vertical.

Ferrite rod antennas¶

Ferrite rod antennas are very suitable for a lightning detector. They are small, can be operated indoors and can even be shielded. The length should not be less than 12cm. Lengths over 30cm make no sense. Two antennas are sufficient, three antennas are a luxury. Regardless of whether it is one, two or three antennas, they should always be operated horizontally. Two antennas should be mounted at a 90 degree angle and three antennas at a 60 degree angle. They can be arranged crosswise or side by side. Blind spots can be eliminated with just two antennas. Alignment in a north / south or west / east direction is not necessary. Shielding is usually not necessary as the input on the preamplifier is symmetrical.

The wire on the ferrite rod antennas is insulated with varnish. This lacquer must be scraped off so that the wires can be connected to the preamplifier. The stripped wires cannot be fastened in the screw clamps of the pin header because they are too thin for that. Either the wires are soldered to the soldering points on the back of the preamplifier at the pin header or a bigger wire is soldered to the wires, which can then be fastened in the screw clamp. It does not matter where the wire with the node is connected to. The knot only plays a role with bipolar preamplifiers. Our preamplifier has a symmetrical input.

Loop Antennas¶

Loop antennas can be made in many ways - in principle, it is just a conductive wire, wound as a coil.

The shape does not matter as it is the area of ​​the total number of turns that determines the strength of the signal. Circular gives the largest area for a given length of wire, but a rectangular or any other shape, may be easier and is equally effective. Magnetic signals in a loop generate a current, so the wire used should be minimum of 0.75mm² and preferably thicker.

Wire Loop¶

3 turn, circle (100cm diameter) ~ Area = 0.5² * Pi * 3 ~ 2,4m² Use 0,75mm² or thicker – lacque or plastic isolated copper wire

Wire Loop - "Classic"¶

Loop antennas has been knows since 30s, so it was obvious to start with this model. 8 turn, square 100cm ~ Area = 8m² Originally made for System GREEN - for System BLUE 3-4 turns is enough.

Multi Turn¶

20 turn, (38cm diameter) ~ Area ~ 0.19² * Pi * 20 ~ 2,3m² (inductance ~ 500μH) Use 1mm² lacquer or plastic insulated copper.

Coax Loop¶

A 3 turn, circle (100cm diameter) ~ Area = 0.5² * Pi * 3 ~ 2,4m² Inner conductor to the terminal 1-2 and the screen from both ends to terminal 3 (shielding) The screen must be broken at the midpoint, as shown below, so it does not short out the signal.

Möbius antenna¶

A 2 turn with a diameter of 1m gives a total area of ​​0.5 * 0.5 * 3.141 * 4 ~ 3,14m² (0.5 x 0.5 x 3.141x 2)/4 = 0.39m2 (The cable is cut midway and the shield from one end is soldered to the inner conductor at the other end and vice versa - that way there will be 4 active turns)

Antenna with a current Transformers¶

Whether we use 4 turns of 1mm² or 1 turn with 4mm² is in principle gives the same result if we use a current transformer. It may be convenient to use a thick copper pipe or copper bar for external antenna.This provides a relatively large current to be transformed to adapt the pre-amplifier.

If we use a 50-turn toroidal current transformer as shown below, we get a relative area magnification of approximately 7 times. A loop of Ø=38cm made of 5mm brake pipe gives a relative area of 0.38 x 0.38/4 x pi x 7 = 0.79 m2.

Examples of möbius antennas with a Transformer¶

Ø=38cm