Medium Aperture Active Loop Antenna Model ALA100LN.
North American version.
New High Gain Ultra Low Noise Figure JFET Design
Note: Power supply no longer provided.
50kHz to 30MHz.
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.
Product Information - click here for pdf
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.
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