Large Aperture Active Loop Antenna N. Am.

Large Aperture Active Loop Antenna Model ALA100LN  N. American version

New low noise FET design

50kHz to 30MHz.

The gain above 10MHz is reduced to reduce excesive Broadcast Band signals.

 The Wellbrook Large Aperture Loop ALA100LN is a specialist's antenna designed for the Long wave, NDB Band and Medium wave DXer.

The antenna uses a 20m circumference thin wire loop to provide optimum S/N. The ALA 100LN uses the similar interference reduction properties as the ALA1530.

The Active Loop Antenna ALA 100LN is a large aperture antenna designed to provide improved performance compared to traditional active and passive antennas.

The new ALA100LN is the third generation of this antenna and uses 8 JFETs in parallel push-pull with optimum noise-less transformer feed-back resulting in a much lower amplifier noise floor. This lower amplifier noise floor is achieved by dynamically decreasing the JFET Source resistance from approx. 60 Ohms to 4 Ohms.  The theoretical noise figure is 0.1dB, however this excludes other circuit loss.

Product Information - click here for pdf N. American version with psu

ACTIVE ANTENNA CONSIDERATIONS

Currently there are several active antennas available providing similar performance.

These active antennas generally fall into two types:

1) Whip and dipoles, responding mainly to the electric field.

2) Loops, responding mainly to the magnetic field

Whip and dipole antennas are more numerous because they easier to design for broadband performance.

The loop antennas are either manually tuned or wideband. The manually tuned antennas can provide excellent results because their selectivity reduces intermodulation products. However, having to manually tune the antenna in step with the receiver is a considerable disadvantage. Thus the broadband loop antenna offer considerable operational advantages. Also it is nearly impossible to obtain a tuned loop antenna that will provide coverage of LW through to SW. In most cases several tuned loops would be required at a considerable cost.

Where active antennas are used in the presence of local interference. The balanced dipole and balanced loop designs provide the best interference rejection. Whip antennas that use the feeder as an RF return path are prone to interference induce on the feeder screen and mains borne noise.

Generally the loop antenna is less sensitive to local interference and static. Also a balanced loop antenna will have a "figure of eight" directivity pattern with deep nulls to further enhance interference reduction.