The Wellbrook Phased Array is a totally
new receiving antenna designed for optimum MW reception. This Antenna
system is only Broadband Phased Array to offer a uni-directional pattern
similar to the Beverage, over 360 degrees with electronic Null Steering.
The design is the result of several years research by Wellbrook’s owner
and chief design engineer Andrew H. Ikin. Trials of this new array have
been performed in the US by experienced MW Dxers using the phasing system
with high performance Active Vertical and Active Loop antennas.
These trials demonstrated that the Phased Array equipped
with elements made from ALA 100 Large Aperture triangular Loop Antennas
(one of the world's best active antennas) provided much lower noise and
improved side rejection than an identical array equipped with Active Vertical
antenna elements. This finding was particularly important for DXers living
in urban areas. Moreover, comparative listening tests indicated that the
Phased Array was equally as sensitive and directional as an 800ft Beverage,
with the added advantage of delivering a much higher rear and side rejection
and deep null steering!
Phased Array Design: The Phased Array provides a reversible uni-directional
reception pattern similar to a Beverage with the added ability for the
user to steer up to 50dB nulls around the back of the array.
The Phased Array consists of a Control Unit and two ALA100 Loop
antennas. Each loop is triangular with just one support pole.
The Phased Array can be expanded to use four ALA100 loop antennas to provide
360 degree coverage.
The Control Unit combines the output of the two antennas using a technique
known as “Delay line Anti-phasing” i.e. the antennas are combined in anti-phase
plus a variable time delay equal to between 40% and 100% of the spacing
of the antennas. This phasing technique provides a uni-directional reception
pattern over a very wide bandwidth with only a minor adjustment to the
controls. This has a considerable advantage over the majority other phasing
systems which require constant adjustment even with small frequency changes.
The ALA100 Loops are powered from the Control unit via the antenna feeders.
The Phased Array Control Unit can also phase two ALA100 loop antennas
to provide bi-directional pattern with both deep side and high angle nulls
just by simple adjustment of the phase control.
The Phased Array Control Unit has an amplitude Balance control
plus a Unique Continuously Variable Delay-line for the Phase control,
this lets the user optimise the Front to Back ratio and for Null steering.
The Control unit has two channels; Phase channel and an Amplitude channel.
The Phase channel has the variable delay line and a very high dynamic
range amplifier. The Amplitude channel provides the variable gain and
also has a very high dynamic range amplifier. Both channels are buffered
and are fed to the receiver output via a power combiner. A significant
feature of the Phased Array, is complete antenna and receiver isolation.
This prevents current from one antenna feeding back to the other antenna
or changes in the receiver input impedance degrading the array performance.
Most other antenna phased arrays don’t provide any significant antenna/receiver
isolation!
The Control Unit is housed in a grey powder coated die-cast enclosure,
6.75” x 4.75” x 2.1” (117x112x56mm).
PHASED ARRAY KEY FEATURES
- Uni-directional pattern similar to the Beverage
- Simple to erect (no control Lines)
- High Front to Back ratio and side rejection
- Up to 50dB null steering
- High dynamic range amplifiers IOP3 +42dBm; IOP2 +75dBm
- Very low noise ALA100 loop antennas
- Lower noise than Active Whip arrays
- 360° with 4 Loops
- 12Volt DC power, ideal for Dxpeditions
- Only requires 40m antenna spacing
The Phased Array is supplied complete with the
Control Unit, 2 ALA100 Head Amplifiers. Additional ALA100s can be purchased
for the 4 loop array.
The user must provide: The Antenna support poles and the
Loop antenna wire, the RG58c feeder cable and a 12v 500mA regulated power
supply
The Phased Array is very simple to use, with just 3 controls;
Direction, Phase and Balance. The Antenna input and Receiver are 5 BNC
and a standard 2.1mm dc connector for the 12 Volt power supply.
Phased Array Operation:- Connect the
Receiver the loop antenna feeders to the respective Control Unit connectors.
Also connect the 12volt power supply to the Control Unit. The Phase and
Balance control should be set to the middle position.
Tune the receiver to a station (mid band) with a steady signal that is
approx. in line with loops selected by the Direction switch. Then change
the direction switch for the same loop pair. The signal should be lower
by several dB with Direction switch set to the 180 degrees from the station.
Then adjust the Balance and the Phase controls to increase the null. Over
the MW band the Front to Back ratio should be approx. 30dB, tweaking the
controls should allow for station nulling of up to 50 dB. However, some
experimentation with all the controls may be required to obtain the best
null especially when the signals are fading.
Maximum F/B will normally be +/- 30 degrees off the back of the loops.
Antenna Positioning:- The basic 2 loop system requires
the loops to be spaced at 40m only. The loops are positioned in line relative
to each other i.e. one loop is positioned North and the other loop is
placed 40m to the South. Where 4 loop system is deployed the other 2 loops
are position as above but in East and West direction. The loop antennas
should be positioned as for as possible from buildings, and sources of
interference In most cases satisfactory results will be obtained by mounting
the antennas close to ground level and at least 20m away from buildings.
A triangular wire loop is recommended for the ALA100 Large
Aperture antenna. The antenna loop is approx. 7m high with a 7m base.
The ALA100 head is connected at the centre of the base wire. A user-provided
7m high pole supports the antenna loop wire. Two 1m user-provided poles,
support the ends of the base wire. The base wire should be approx. 0.5
metre off the ground.
Vertical and Broadside Null
2 loops at 180 degrees
0 Phase setting
Uni-direction
2 loops at 138 degrees
Mid Phase setting
Uni-direction, max groundwave null
2 loops at 128 degrees
Mid Phase setting
Phased Array Control Unit
Click here for REVIEW of
Phased Array
Design/specification subject to change without notice
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Wellbrook
Communications