Schwarzbeck FMZB 1512 Active Handheld RX Loop Antenna

The Schwarzbeck FMZB 1512 is an active, shielded handheld loop antenna with nearly constant antenna factor over the entire frequency range. It can be used for testing according to CISPR, MIL, FCC, EN, ISO, ANSI, ETSI and many other standards.

It can be used for the frequency selective measurement of magnetic fields (or fictive electric field) in the frequency range from 9 kHz to 30 MHz.

Since it is directional sensitive one can locate field sources.

The active loop antenna is especially suitable for mobile applications, for instance if used with a handheld spectrum analyzer. Combined with a CISPR 16 EMI-receiver the FMZB 1512 makes a convenient field strength measuring system with low noise and pulse measuring capabilities.

Since the FMZB 1512 is a highly sensitive, light weight magnetic loop antenna it is particularly suited for the direction finding of signal and noise sources.

The FMZB 1512 is equipped with 8 NiMHMignon cells (AAA) to keep the weight as low as possible for mobile use. The battery voltage is indicated by a LED. A green light shows normal operation and a red light means that you have to recharge urgently. Although it is possible to measure while recharging, we do not recommend to do so because most NiMH chargers operate in pulsed mode and create unwanted disturbance.

The shielded housing comes with a tube of 22 mm in diameter so it can be mounted on tripods with commonly used mast adapters (i.e. the AA 9202).

Schwarzbeck FMZB 1512 Operation

The active loop antenna FMZB 1512 can be switched on with a toggle switch at the top side of the housing. Therefore the switch has to be put into the position “ON”.

After turning the device on the LED which is located left from the switch will be illuminated. When it is illuminated green, the battery is charged sufficiently. When the LED glows red, you have to charge it by all means. If there is no LED indication, the battery is totally discharged. Exhaustive discharging should be avoided in any case because the lifetime of batteries can suffer.

To charge the accumulators you have to connect the charger to the socket at the right side of the housing of the FMZB 1512. The charging time is typically 62 hours.

Avoid shorting the charging contacts! Protect from moisture!

The gain can be adjusted by the rotary switch. The maximum possible gain corresponds to an electric antenna factor of kE = 20 dB/m and can be decreased in 3 dB steps down to kE = 53 dB/m. Since the frequency response of FMZB 1512 varies slightly above 10 MHz when switching the attenuator, the recommended setting for accurate measurements is the switch position kE = 20 dB/m. The supplied calibration data refers also to the switch position kE = 20 dB/m.

The probe is directional sensitive. You can find the maximum level by turning the probe. The result depends on the frequency as well as on the distance to the signal source.

Sources of fields can be located.

Schwarzbeck FMZB 1512 Basics

In the near field of a radiation source electric and magnetic field components have to be examined separately. A common definition is a distance < λ/2π as near field. Keeping in mind that a frequency of 100 kHz corresponds to a wave length of 3 km (approx. 1.9 miles), usually measurements up to several megahertz can be considered to be near field measurements.

Schwarzbeck FMZB 1512 Construction

Magnetic field probes have to suppress electric fields as far as possible. This is achieved using an electric shielding of the loop (tube) which is disconnected in the middle to avoid a magnetic short circuit of the winding. Basic physics shows that the unloaded voltage of a loop is proportional to the frequency. Active probes overcome this problem by measuring the short circuit current of the loop.

Schwarzbeck FMZB 1512 Field strength range

FMZB 1512 are the best choice when small field strengths have to be measured. The lower limit is better than 1 µA/m. The maximum fieldstrength values of 126 V/m or 0.33 A/m can be measured using the switch positions kE ≥ 44 dB/m.

Magnetic probes and fictitious magnetic fieldstrength

The Loop antennas of the FMZB series will always and only measure magnetic field strength.

The undesired sensitivity for the electric field strength is considerably lowered using a loop shielding.

Nevertheless you can transform the “fictive” e-field strength by a value of +20 dB/m.

When far-fields are being measured, one has to add the conversion factor for e-fields (kE) in dBµV/m to the measured result of the receiver in dBµV.

This is based on the fact that in the far field of an antenna electric and magnetic field strength are related via the characteristic field impedance of the free space (377 Ω). The conversion from magnetic field strength to fictive electric field strength does not depend on the frequency and is 51.5 dB (=20lg(377Ω).

F [dBµV/m]=G [dBµA/m]+51.5 dB
F: Electric field strength-level
G: Magnetic field strength-level Z = 120 πΩ = 377 Ω

or:

E [V/m]=H [A/m] x 377Ω
E: Electric field strength
H: Magnetic field strength