Antenas de aro

Ultra low noise Active Loop Antenna Model ALA1530LN

A new version of the world famous Wellbrook Active Loop ALA1530

50kHz-30MHz 1m dia. Aluminium Loop

This Balanced low impedance Magnetic loop has enhanced performance compared to shielded and Moebius loop types.

The new JFET design affords a considerable reduction of noise compared to low cost loops using MMIC (Monolithic Microwave Integrated Circuit). MMICs are designed for Microwave use and therefore are unsuitable for LF to HF loops. Furthermore, MMICs use integrated resistor feedback, which limits the noise figure to a minimum 3dB at HF. At Medium Frequencies loops using MMIC amplifiers can have a Noise Figure as high as 8dB plus high IMD (Intermodulation Distortion).

The ALA1530LN has a noise figure of approximately 0.2dB which give a noise floor that is 13dB lower compared to a similar gain loop with a noise figure of 3dB.

This antenna and its big brother, the ALA1530LNPro Imperium are the only 1m dia. Active loops in production to use an ultra low noise JFET design. The loop has recently had a significant design change to improve LW/MW and SW reception. The ALA1530LN has been engineered to increase the LW and MW signal to noise ratio s/n by up to 10dB and provide an increased s/n on the HF bands. The LW and MW 3rd order IMD is now approx. 20dB lower. This being a combination of reducing the gain a little and the lower IMD of the JFETs

The new ALA1530LN is the second generation of this antenna and uses 8 very high gain JFETs in parallel push-pull with a Bipolar transistor cascode stage for extended bandwidth. A very low amplifier noise floor is achieved by dynamically decreasing the JFET Source resistance to a fraction of an Ohm. This is achieved using a proven technique developed in the 1980s by coupling the FET Gate to the Source with a phase inverting transformer.

The loop works by designing amplifier so that the very low noise of the loops real resistance is mismatched to the input impedance of the low noise amplifier. Hence, reducing the amplifier noise floor by up to 13dB compared to more conventional low noise amplifiers. Also JFETs are less noisy at low frequencies compared Bipolar transistors. The amplifier also has a rising input impedance versus frequency to match the loop's reactance; this together with Ultra low noise JFET design is a technological breakthrough.

The mechanical design is now improved to afford increased reliability and to facilitate ease of servicing:

The amplifier is now house in a separate module, thus isolating the electronics from the mechanical stress caused by wind loading on the loop. The amplifier to loop wire terminations use tin plated silicone insulated wire and crimp terminals rated down to –40 Celsius. The module sits on of the loop box and is secured by stainless steel screws. The base of the loop is now reinforced with an acetal rod to minimised damage due to weather extremities.

The amplifier module can be easily replaced in the unlikely event of a failure, without the customer having purchase a new loop antenna with the associated high shipping costs.

A resettable fuse and a power on LED are now fitted to the Antenna Interface. Additionally a power limiter is fitted to reduce overload of receivers co-located with transmitters.

This unique broadband magnetic antenna is only 1m diameter and rotatable to provide deep nulls to reject noise and interference. This new broadband untuned Loop antenna is the only active antenna designed specifically to reject locally radiated and mains borne noise from TVs, computers, mains wiring etc.

The Loop antenna responds primarily to the Magnetic Field and rejects locally radiated Electric-Field noise providing far lower noise reception than active whip/dipole antennas. Compared to active whip/dipole antennas, the Loop will reduce locally radiated noise by up to 30dB and mains borne noise by up to 60dB. The ALA 1530LN has 30dB nulls to further reduce interference.

It is ideal for small gardens, indoors and directional reception using an antenna rotator.

The ALA1530LN offers significant advantages over the traditional tuned Loop, because the Loop can be used away from local interference. Whereas, a tuned Loop has to be positioned next to the receiver where there are high levels of local noise.

This antenna is probably the most advanced broadband active Loop antenna available to the Radio Enthusiast, offering professional performance at an affordable price. The Loop antenna is supplied with an Antenna Interface and a 12-volt regulated Power Supply.