Wellbrook ALA1530

Wellbrook ALA1530LNP HF Antenna

The ALA1530LNP is the second loop in the IMPERIUM range of the world famous Wellbrook Active Loop ALA1530 long, medium and shortwave antenna.

This Balanced low impedance Magnetic loop has enhanced performance compared to shield 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 an 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).

  • shoc can supply Wellbrook to EU countries
  • A linear regulated power supply is recommended, because switched power supplies can cause interference!
  • 50kHz-30MHz 1m dia. Aluminium Loop
  • As of April 2021 the amplifier gain has been increased to 28dB
  • Ultra low noise JFET design compared to conventional low noise and MMIC amplifiers
  • Unique two transformer Norton amplifier ensures good performance in a strong signal environment
  • No tuning necessary or matching unit
  • Figure of eight directivity and deep nulls to further reduce interference

The ALA1530LNP 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 together with the ALA1530LN are the only 1m dia. 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 antenna gain is increase by 9dB and the LW and MW signal to noise ratio s/n is up to 10dB higher, with an improved s/n on the HF bands. The LW and MW 3rd order IMD is now approx. 20dB lower when compared to the ALA1530 and the ALA1530S+. This being a combination of altering the gain distribution and the lower IMD of the JFETs.

The new ALA1530LNP 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.

A unique 2 transformer push-pull Norton amplifier with a higher HF gain is now fitted in the Antenna Interface. MW OIP3 has been increased to +55dBm; thus giving this active antenna one of the highest third order intercept points in its class.

This new antenna is believed to be the highest gain active loop to provide coverage from LF to HF with low Intermodulation and an exceptionally low amplifier noise floor.
The loop works by designing the 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 10dB 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.

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 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 1530LNP has 30dB nulls to further reduce interference.
It is ideal for small gardens, indoors and directional reception using an antenna rotator.

The ALA1530LNP 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. Wellbrook will no longer provide a 12V power supply with any antenna products.

Technical data

Feature Data
Frequency range 50 kHz to 30 MHz
Loop Diameter 1 m
Power consumption 12 volts at 500 mA
Amplifier Intercept point typically (MW Band) OIP2 +90dBm, OIP3 +55dBm
Amplifier Noise Figure Approx. 0.2dB
Output impedance 50 ohms BNC
Max. Field strength 400V/m or 1.0A/m pulse