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Hardware Review
ALA 1530 - Results in the field (II) In one word I can say that this active magnetic loop, as receive antenna, is more useful than any long wire or dipole flooded in QRM. I prefer to not say *very useful* for several reasons explained below. However my appreciation is very positive in regards with its overall performance when it is connected to a performing receiver (showing a good sensitivity and selectivity). Without having the possibility to test both magnetic loops with a spectrum analyser I can only test the audio performance of the antenna on stations or beacons I heard on bands. First the SWR Wellbrook states that the ALA 1530 and other models have no SWR. In fact all active antennas don't quote SWR curves because the SWR is dependant on the source impedance of the receiver. i.e. the output of an active antenna is broadband amplifier driving the feeder. Therefore the impedance matching is not required. It is even forbidden to activate the antenna tuner as it will send about 10W in the antenna and there is a chance that this power damages the transistors of the interface. Practically the interface transistors will support this low current as long as the tones are sent in CW at very low power (1-10W) but I prefer to tell you to avoid such practice. The antenna position and location As I have bought the magnetic loop exclusively for indoors usage, I move the loop in various places in the living room, near or far from the walls (made of bricks) or from the windows located street side. When I placed the loop on the ground, under the window, in front of the radiator turned off, the QRM increased a little (1 S-point or +6 dB) and disappeared when I placed the loop back just in front of the window, 1m high and behind the veils. The QRM reduced a bit more when I placed the loop at ground level, 3m away from the window, near a supporting wall. So I definitively placed it at that location, behind a door. This is strange but it is in that position that I capture best all stations with the less QRM. The fact to change the loop orientation from vertical to horizontal, to turn the loop of 90° or to tilt it at 45° didn't change the signals or the QRM intensity, at least in my location. However the fact of changing its orientation in regards with NSEW positions changed sometimes the reception of noisy signals or AM broadcasts in the lower bands (see below). So I can already conclude that this kind of antennas are not very sensitive to their position relative to the signals but well to the distance to concrete or maybe to dense objects containing metal. Wellbrook suggests also to place the ALA 1530 at at least 10m from any RTX or emission antenna to avoid intermodulation to which it is more sensible than the ALA 330S. I also made a test installing the loops in the cellar, what means in a room under ground level made of concrete all parts, which walls are not more tick than the one of the appartment. Amazingly, I continued to listen stations with nearly the same intensity as at the second floor. I am not sure however you could get the same result in a building which walls are made of a mix of concrete and a mesh of metallic wires. Stations signals In the HF bands signals are globally stronger with less QRM using the loop than any wire sloper, mainly in bands from 17 to 10 m, with the best noise reduction in the 17m and 12m bands where the QRM dropped from S-9 to as small as S-1 ! For the first time for many weeks I can hear in LX stations that were flooded previously in the QRM. That means that is this special case the signal strenght increase of 48 dB ! As strange as unexpected on the 20, 40 and 80m band, the loop picks up the same and sometimes signals less strong than my dipole or the long wire. I cannot explain this phenomenon. In the best conditions the S-meter of stations increases a little but usually it stays at the a same level of intensity or drops of one or several points using the magnetic loop. I lost up to 12 dB using the loop... However even when signals display a lower intensity on the S-meter, the QRM is reduced. In a few rare occasions the QRM increased when I used the loop. In such cases in moving the loop I can improve the reception and still reduce the QRM. In
the 160m band, where the loop is theoretically not adapted, the QRM
is also much reduced with the loop, dropping for example from 59+10 to S3
but this band was free of OM at the time of my tests and I checked
the signals intensity with beacons. This signal increase is
equivalent to drop the QRM of 42 dB over the signal ! Below 3 MHz, switching to AM mode the few broadcasts I listened to with the loop were audible but their signals is usually a few points below the strength of signals that I receive with the dipole or the long wire (58 instead of 59 or 6 dB down). In practice it could be useful to rotate the loop not only for LW listening but also for HF listenings but it is not really practical in my appartement as the loop is then right in the middle of the passage ! I
discussed with the manufacturer as I wondered that the ALA 1530 or 330S loop
displayed on some frequencies a lower gain than my dipole. Andy Ikin explained me
that "it was necessary to prevent antenna overloading and intermodulation.
Generally the lower noise performance of the loop outweighs the higher signals and QRN
from Long wires and active Whips. The low gain of the ALA 330S below 3 MHz prevents
close Megawatt AM broadcast from overloading the antenna and the RX. This is a plus feature
for some users". I cannot contest this fact.
About
peripherals Peripherals
like dimmers, battery rechargers or computers used
nearby the RTX are strong RFI emitters. But these loops are much less sensible to these RFI than
a dipole or a long wire. In short, although the loops capture
also their interferences, their intensity displays a level much
lower than using these wire antennas (up to 2 S-points or 12 dB). In other words
that I mainly addresses to listeners, be no more
afraid to use your computer and periphals when your receiver is switched on;
this is an excellent news ! Troubleshooting Few
problems can happen using Wellbrook antennas if you respect
only one rule : do not try to emit with them !
Among the easier
problems to diagnostic, if one or another day you do no more listen any station
excepted the nearest and the loudest, with a drop of 5 to more
than 9 points on your S-meter, remove the fuse. If there
is no difference, if the background white noise or signals display the
same intensity your fuse has probably blew out. Check it and
replace it if necessary. If this component is still good, check your cabling
system for a short-circuit; it could be cut in the BNC
connector. Once repaired check its resistance. If the situation
does not change then you probably experimented some damage in
the interface. Do contact Wellbrook for advice and get more
information to test or to replace the failed component. As a
last resort you will have to send the failed component back to
the manufacturer at your charge by registered mail. The delay
for replacing may exceed 4 weeks.
By
way of conclusion The
"pluses"
of ALA 1530 receive antenna :
-
Highly recommended when space is limited
-
Suited for LW and HF listenings -
Reduces drastically QRM over 7 S-points or 42 dB in bands from 17-10m bands (see
appendix, p3)
-
Requests no antenna tuner for matching impedances -
Easy to assembly in a few minutes -
Very light antenna, not bulky compared to any passive antenna -
Quality of assembly kit -
Not too expensive in regards to its performances The
"minuses"
of ALA 1530 receive antenna : -
Few or no QRM attenuation from 20 m and lower bands at night (see
appendix, p3) -
Reduce a little the signal intensity in the 30-40m bands in HF and below 15
MHz in AM -
Should be remotely rotated in its plan to increase signals and reduce QRM -
User manual unappropriated, lack of technical advices (on paper or
on website) for the beginner -
For a novice user, basic accessories missing (BNC, power supply)
with risk of errors when assembly the parts -
The ALA 1530 is a bit more sensitive to intermodulation than ALA-330S -
This is a receive antenna only (by design, I do not complain) -
Very slow response from the manufacturer to ship replacing parts (2 months, no stock) Should
I place another order if needed ? If I had no free space to
tight a dipole, erect a vertical or a beam, e.g. if I should be
restricted to the space of my appartement without possibility to
install an antenna outdoor, I should do. But I should probably
purchase a still more sensitive model, if there is. Of course, being
today licensed the problem is different and I would buy a vertical
or a beam. For
more information The
ALA 1530 as well as other receive loop antennas can be
obtained from Wellbrook
Communications, Wellbrook House, Brookside Road, Bransgore,
Christchurch, Dorset, BH23 8NA, U.K. The
ALA 1530 antenna costs £159 plus p&p (pricelist 2006) or about 230 €
charges included for Europe/overseas. Completed with all requested
accessories (power supply, BNC and coax) it will cost you about 250 €
or $290. For the same price and for the US market only, it is also
available with an external PSU. A second model is sold for the
same price with a polyethylene loop (ALA-1530P). Hope
this helps and be a useful contribution on a subject too rarely
tackled. A copy of this review is available on eHam.net. Since
this publication (2003) several licensed OMs experimenting much QRM too told me
that my review convinced them to buy the ALA 1530 for receive
purposes. I
thank very much Andy Ikin from Wellbrook for his advice and
technical explanations. Appendix Figures and measurements in the field
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