loop for small gardens
Andrew Ikin says his range of products are aimed at urban
dwellers who need to keep background noise to a minimum.
has developed the ALA 1530 active loop antenna, designed for use
in small gardens where hanging a passive longwire antenna would
be physically impossible. The unit comes with a head end unit,
an antenna interface and a 12 volt regulated power supply. The
user has to supply the feeder cable. The 1 metre loop is made
of aluminium (a light-weight polyethylene version-is also available)
and is designed to operate near the ground where the ground reflected
wave and the incident wave are in phase.
I have a Wellbrook ALA1530 antenna on the roof. I'm living
in a noisy area in the suburb of Antwerp. The ALA gives me
the reception quality from decades ago. I've made a daytime
long- and mediumwave bandscan and put it in an Excel file,
which can be downloaded for comparison.
loop reacts mainly to the magnetic component of the electromagnetic
wave and has a figure of eight reception pattern. In use very
close to a 400 kW medium wave station we did suffer from some
faint breakthrough problems when trying to pick up weak signals
coming from the same direction. In that respect we found that
on medium wave the Wellbrook loop was much better than the Liniplex
loop we tested a few years back, but not quite as good as the
indoor mediumwave loop from KIWA. The indoor antenna was used
in a situation when there were no computers or fluorescent lights
operating in or adjacent rooms.
the medium wave range though, the KIWA loop is not suitable.
When the Wellbrook loop was facing 90 degrees away from the medium
wave station, no problems were encounted. The loop amplifier has
a third order intercept point around 42dBm, confirming the manufacturer's
specifications and that is fairly constant throughout the frequency
range of 150-30 MHz. If you use such a garden loop for medium
wave listening, then a rotator will be needed if you want to hear
stations from all directions. The noise level was indeed low,
comparable to the T2FD (the T2FD was slightly quieter on the tropical
bands around 60 metres) and better than a simple longwire and
a dipole set up for comparison. We used an AOR-7030 and JRC NRD-535
for our listening tests. We installed the loop in September 1997
and did listening tests over a period of four weeks.
note that Wellbrook use the BNC connector as standard
rather the PL-259 connector. After waterproofing the connection,
we're curious to see how it survives the Dutch winter.
The Wellbrook Loop Antenna costs £119.95 including UK Value Added
Tax (post free in UK and Ireland), plus £20 shipping costs to
addresses outside the UK. Note however, that the loop is not available
in North America.
More information is available from Wellbrook Communications, Wellbrook
House, Brookside Road, Bransgore, Christchurch, BH23 8NA, UK Tel:
+44 1425 674174.
The same company manufactures an antenna feeder isolator, which
they claim, stops noise getting into the feed line through mainsborne
interference. A side-by-test alongside a similar device called
the MT isolator from RF Systems is being organized at press time.
Results in a future edition of the WRTH since it takes some extensive
listening to be fair to all devices.
However, it is already clear that the biggest benefit from devices
like this comes when there is heavy local electrical interference
(e.g. a hotel full of televisions, an electrical substation or
business with lots of computers.) Once again, when space is no
object, passive antennas are always best.
Published with permission from WRTH editor.