The transmit loop antenna HFRA 5159 was designed to generate well defined magnetic fields in the frequency range from DC to 400 kHz. With the slightly reduced performance the loop can be used in the frequency range up to 2 MHz. The loop, consisting of 28 turns, is shielded against E-fields. The nickel-plated brass housing contains resistors to verify the loop current by voltage measurement. The loop antenna has a flat frequency response over the entire frequency range. The loop can be mounted at its female large camera thread.

The generated magnetic field is proportional to the loop current. A tabular indicates the field-strength values in A/m and dBμA/m to be expected with the loop current of 100 mA. Additionally, the relative decrease of magnetic field-strength referred to as the center of the loop antenna can be found. The lower magnetic field strength can be achieved by scaling the current to the respective value. With a feed current of 10 mA instead of 100 mA, the tabular values decrease by a factor of 10, which corresponds to a reduction by 20 dB in logarithmic measure. All specified magnetic field strength refers to the component which is perpendicular to the loop-plane.

Application:

The HFRA 5159 comes with 3 BNC connectors. Connector A is used to feed the loop with a 50 Ω source with constant voltage, which generates a constant magnetic field-strength versa frequency. Connector C is used to monitor the loop current by measuring the voltage drop across a 10 Ω resistor. This operation mode uses a linearisation of the loop current by a series resistor, which causes a flat frequency response, but the achievable field strength is limited. Alternatively, the loop antenna can be driven through Connector B, which presents the loop inductance in series with the 10 Ω resistor. In this case, the loop current has to be checked by measuring the voltage drop across the 10 Ω resistor. This operation mode allows us to generate higher field-strength levels but requires current monitoring and input voltage adjustment for each frequency. We recommend using voltage measuring equipment with high impedance to measure at connector C.

Specifications:

• Frequency range: DC-400 kHz
• Loop diameter: 250 mm 
• Resonance frequency: 600 kHz
• Number of turns: 28
• Current control resistance: 10 Ω
• Inductance: 450 μH
• Series resistance of the turns: 2 Ω 
• Parasitic parallel capacitance: 160 pF
• Maximum current socket A: 70 mA
• Input impedance socket A: 1.26 kΩ
• Maximum current socket B: 110 mA
• Input impedance socket B: see diagram
• Maximum power: 5 W
• Dimensions: 260 x 305 x 80 mm
• Connections: 3 x BNC
• Attachment: 3/8 "
• Weight: 450 g