Wellbrook Communications

This Active loop, like its ALA 1530 cousin sets new standards for the listener. For the first time it is possible to reject locally radiated and mains borne/power line noise and still provide improved reception compared to larger antennas. 1m dia. Aluminium loop is designed for outdoors, even close to ground level.

The loop has a frequency range from 150kHz to 30MHz and matches directly to the receiver. The ALA 330S is probably the only Commercial Active antenna available to the Radio Enthusiast to provide directional noise reduction in the SW bands.

The Loop can be mounted remotely from the receiver away from local interference. Thus ALA 330S generally has lower noise reception compared to manually tuned indoor loop. Furthermore, traditional wire antennas require a lot of space and can pick-up local noise.

BROADBAND LOOP FEATURES

• Very low intermodulation products ensures good performance in a high signal environment
• MW/AM Broadcast attenuator to reduce receiver overload
• Up to 30dB rejection of local noise compared to active whip antenna.
• Figure of eight directivity and deep nulls to further reduce interference.
• Lower noise than indoor tuned loop
• Rejects Power-line/mains borne noise.
• Rugged construction, 1m diameter aluminium loop, supplied with Interface and 12 volt PSU, feeder connectors and rotator mounting hardware
• Easy installation, works close to ground level

LOOP ANTENNA ADVANTAGE

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 330S Broadband Loop has been specifically designed to reduce intermodulation products to a minimum. The second order and the third order intercept points are typically +80dBm ( IP2 ) and +43dBm ( 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 ALA 330S is supplied Antenna Interface, connectors and a regulated power supply ( UK, Ireland and North America only ). 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.

The ALA 330 should be positioned approximately 5m away from any buildings.

TECHNICAL INFORMATION

TYPICAL INSTALLATION

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.
An active whip or dipole antenna will also pick up high levels of interference.