Wellbrook ALA100

Wellbrook ALA100LN HF Antenna

The Active Loop Antenna model ALA100LN is a medium aperture antenna designed to provide improved performance compared to traditional active and passive antennas. The ALA100LN has two modes of operation; at medium and low Frequencies the antenna is a high efficiency broadband loop; for high frequencies the antenna has a response similar to a long wire

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  • A linear regulated power supply is recommended, because switched power supplies can cause interference!
  • New High Gain 26dB amplifier allowing for a smaller size loop.
  • Much higher signal handling compared to MMIC designs and 5V USB driven antennas.
  • Balanced low impedance Magnetic loop
  • Medium aperture: Ideal for NDB, LW/MW/SW DX.
  • Ultra Low Noise figure for enhanced weak signal reception
  • Up to 30dB rejection of locally radiated and power-line noise compared to an active whip
  • Very low intermodulation products ensures good performance in a strong signal environment.
  • Figure of Eight directivity and deep nulls to further reduce interference.
  • No tuning necessary or matching unit; No planning problems, works close to ground level.

This antenna has recently been upgraded to extend the bandwidth from 10MHz to 30MHz. The amplifier gain has been increased to approx. 26dB; thus allowing for use with a smaller loop.
The Wellbrook Medium Aperture Loop ALA100LN is a specialist's antenna designed for the long wave, NDB band, medium wave and short wave DXer. The antenna is designed for a user-provided thin wire loop; 8-10m circumference. The ALA100LN has similar interference reduction properties as the ALA1530LN.
The Active Loop Antenna ALA100LN is a medium aperture antenna designed to provide improved performance compared to traditional active and passive antennas.
The new ALA100LN is the fourth generation of this antenna and uses 8 high gain low noise JFETs in parallel push-pull, cascode with the proven technique of coupling the FET gate to the Source with a phase inverting transformer resulting in a much lower amplifier noise floor. This lower amplifier noise floor is achieved by dynamically decreasing the JFET source resistance from approx. 10 Ohms to less than 1 Ohm.

The noise floor is approx. 7.0dB lower compared to other amplifier types with an equivalent 10m loop inductance.

The ALA100LN Loop Antenna comprises of a loop/amplifier head unit together with an antenna interface.
RG58C 50 ohm coaxial feeder cable is recommended for the
antenna. The maximum feeder length is 100m. The antenna interface feeds the 12 volt dc power to the antenna. The wire loop is provided by the user. This can be supported by a tree or light weight wooden poles 2-4m high spaced 2-5m apart. Alternatively the loop can be loft mounted or simply attached to the inside or outside wall of the home. However, for lower noise performance, the ALA100LN should be positioned away from sources of interference such as fluorescent lights, TVs, computers and electrical wiring. In most cases satisfactory results can be obtained by mounting the antenna near ground level and at least 6m from buildings.
The ALA100LN can also be mounted on to an antenna rotator using a simple 3m x 3m wooden frame to exploit the Loops directional characteristics. Alternatively an 10m circumference triangular loop can be used.

Technical data

Feature Data
Frequency range aprox. 50 kHz to 30 MHz, depends on loop layout
Loop Diameter 8-10 m
Power consumption 12 volts at 500 mA
Amplifier Intercept point typically (MW Band) OIP2 +90dBm, OIP3 +50dBm
Nominal gain: 26dB at 1MHz
Amplifier Noise Figure Approx. 0.2dB
Output impedance 50 ohms BNC
Max. Field strength 400V/m or 1.0A/m pulse