Wellbrook Communications

The ALA1530 is a compact Active magnetic loop antenna primarily designed to provide improved performance over conventional passive and active antennas. This loop has been production for over 10 years and has recently had significant design changes to improve LW and MW reception.

This Active loop sets new standards for the listener. For the first time it is possible to reject locally radiated and mains borne noise and still provide improved sensitivity compared to larger antennas.

1m dia. Aluminium loop is designed for outdoors, even at ground level. The loop has a frequency range from 40kHz to 30MHz and matches directly to the receiver. The ALA 1530 is probably the only Commercial Active antenna available to the Radio Enthusiast to provide directional reception of the LW and MW bands.

The loop can be mounted remotely from the receiver away from local interference. Whereas, traditional antennas require a lot of space and can pick-up local noise.

Supplied complete with Antenna Interface and a regulated power supply.

BROADBAND LOOP FEATURES

• Very low intermodulation products ensures good performance in a strong signal environment
• New design has much lower MW Intermod.
• Up to 30dB rejection of locally radiated and power-line noise compared to an active whip
• Figure of eight directivity and deep nulls to further reduce interference.
• Ideal for LW/MW with antenna rotator
• Rugged construction, 1m dia. aluminium loop,supplied with Antenna Interface and 12 volt PSU
• No tuning necessary or matching unit
• No planning problems, works at ground level

LOOP ANTENNA ADVANTAGES

The active antenna solves the problem of impedance matching to the feeder and yet the performance is comparable with larger antennas. However, most active antennas are the whip type and respond mainly to the electric-field. The Broadband Loop responds primarily to the magnetic-field, this ensures high rejection of nearby electric-fields.

The intensity of the electric-field is usually higher than the magnetic-field when an antenna is close to interference sources such as TVs florescent lamps, mains wiring etc. Therefore, by rejecting the electric-field there will be a reduction in local interference compared to other types of active and passive antennas. Interference reduction is further enhanced by the deep nulls of the 'Figure-of-Eight' directivity pattern.

INTERMODULATION

Some active antennas generate intermodulation products which can appear as spurious signals interfering with reception. This interference or second order intermodulation is caused by non-linearity in the amplifier, producing signals which are the usually the sum and difference of strong Broadcast stations.

The ALA 1530 Broadband Loop has been specifically designed to reduce intermodulation products to a minimum. The second order and the third order intercept points are typically +70dBm (IP2) and +40dBm (IP3) respectively. Thus the level of the intermodulation products are generally below the atmospheric and man made noise.

ANTENNA DESIGN

The Loop antenna consists of a rigid aluminium loop and a balanced gain optimised broadband amplifier using low noise RF power transistors. The amplifier is encapsulated in resin and housed in a uPVC box, this ensures reliable operation in all weather conditions. The antenna provides low noise performance, large signal handling ability. Rejection of mains borne noise is accomplished by using a balanced amplifier so that the feeder does form part of the antenna return path.

The ALA1530 is supplied Antenna Interface and a 12 volt regulated power supply. RG58C 50 ohm coaxial feeder cable is recommended for the antenna. The maximum feeder length is 100m. A 1m coax. lead connects the Antenna Interface to the receiver. A plastic loop version is available; the ALA1530P.

The ALA 1530 should be positioned approximately 5m away from any buildings.

TECHNICAL INFORMATION

NEW ALA 1530+ Upgraded Version NEW


TYPICAL INSTALLATION

N.B. The Antenna Interface is not used with the ALA 2000

CONCEPTUAL ILLUSTRATION OF THE HIGH ELECTRIC FIELD COMPARED TO
THE MAGNETIC FIELD CLOSE TO A LOCAL INTERFERENCE RADIATOR

N.B. The Loop nulls will also further reduce interference by up to 30dB.

Radio Active

WRTH 1998
World Radio TV Handbook

CQ Magazine -
Japanese