Megaloop MLA-30+ active antenna

If you are not a regular reader and you have just landed on this site, to follow the thread of why I am reviewing this antenna you can start reading this note and this other one.

If you don't have time or don't feel like it, I'll summarise it for you. I got this antenna for use with a SDR (software defined radio).

The antenna

The Megaloop MLA-30 is an active antenna for loop or wideband loop reception working between 500KHz and 30 MHz with good response for shortwave and HF.

It is an inexpensive Chinese-made antenna with no known brand name or manufacturer, any of those sold may be a copy of a copy of a copy of a copy.

It is a Chinese design "similar" to the "Megaloop FX" of the"Bonito" brand, but at a price about ten times lower. The actual design is most probably based on the "Active 3-30 MHz Hula-Loop Antenna for Shortwave".

But before we get into the installation, performance, pros and cons, let's take a look at how the product is presented and what you get when you buy it.

Piece by piece

It arrives in a normal package in an anti-static bag with just enough protection to ensure that the parts are unlikely to suffer significant damage in transit.

Includes everything you need to assemble it, no cutting, measuring, adjusting or setting up. Anyone can assemble it in minutes. In fact, it doesn't even come with instructions.

The module with the antenna, which contains the board, is sealed and inside is the board buried in resin to ensure waterproofing if used as a fixed antenna outdoors. Some people have already taken it upon themselves to open it and put the mass in boiling water to dissolve the resin and examine the board. You can see it here.

Image courtesy of Matt, M0LMK

It comes with 10 metres of thin RG174 coaxial cable with SMA connector and two wing nuts to attach the ring.

The ring is a thin and light, but very strong stainless steel wire. Once unfolded it forms a circle of about 62-64 cm in diameter

Finally we have the device that will feed the antenna signal amplifier or what is the same, a Bias Tee that sends a direct current through the same coaxial cable, a 60 cm patch cord with SMA connectors and two screws to fix the module to our tube, plus a USB cable to feed the Bias Tee.

It is based on the Texas TL592B chip, which is a two-stage video amplifier with differential inputs and outputs(Source).

Installation

The set does not include a stand, so you have to make your own stand to mount it on. You can place it on anything like a wooden or PVC pole, as you like. Any support that acts as a long or short pole will do as long as it is not metallic as the hoop will be in contact with the tube.

I have chosen a PVC tube 32 mm thick and 2.5 metres long, which I will finish off with a cap to give a minimum aesthetic finish to this domestic mast and to prevent water from getting into the tube.

There you have the previous graphic summary of the thing.

Something I didn't find in the thousand reviews of this antenna (a few years ago there wasn't a radio amateur who hadn't reviewed it) was the module measurements, necessary to decide the thickness of the tube.

A notch is made at the top of the tube, a couple of centimetres beyond the end of the plug, so that the ring rests on the groove created.

In total, the antenna cost 38. 50 euros plus 8 euros for the tube and a small pack of clips.

The only thing left is to mount the ring on the module and fix it with the wing nuts and screw it to the tube with its two screws (you can also reinforce it with a pair of clips hugging the tube). Try to get a more or less exact circle. It will still work if it is not a perfect circle, but it will be thinner if you can adjust the ring well.

At this point, everyone will have to make the installation that best fits their location. In my case, as I don't have access to a roof (because there is no roof, it's all roof) I have put the tube on a balcony with a couple of clamps and clips on the railing so that it can be disassembled, moved, moved and rotated without difficulty.

To test the MLA-30 we only need to connect the antenna cable to the Bias Tee and the pigtail to the receiver. After that it is enough to power the Bias Tee with a power bank if you don't have enough space for another power adapter. A normal 10,000mAh power bank will last at least three days at a rate of six or seven hours of daily use. That's plenty.

With a higher-capacity one, it could last for weeks. Of course, when it drops below 30% or 25% charge, the Bias Tee tends to shut down.

(The RTL-SDR V4 does not need this Tias Bee, as explained below).

Thanks to a comment from Hans Wörzt (tnx!), I discover that the RTL-SDR Blog V4 does not need the Bias Tee included in the antenna because it has its own one. I mistakenly thought that the LED on the dongle's Bias Tee would light up when an external one was plugged in, but no, the V4 has its own built-in Bias Tee.

It was Hans' comment that tipped me off.

You do not need the little Bias Tee box that came with the MLA-30+ if you're using the RTL-SDR Blog version 4 dongle, as this has its own Bias Tee built-in. Just connect the long cable emanating from the pre-amplifier box at the antenna and connect it directly to the SMA on the SDR. Then, to activate its built-in Bias Tee, just check the Offset Tuning option in SDR#. If it is active a tiny red LED besides the SMA should light up. This simplifies the setup quite a bit. You can activate the Bias Tee also from the command prompt in Windows, using the 'rtl_biast.exe' executable.

*In the case of the SDR++ programme, it has a "Bias T" option to activate it.

Here are a few free snapshots just for the sake of showing off the tube.

Under the cap I put a couple of turns of insulating tape to tighten it a bit, although you can also seal it if you want to leave it fixed.

The rains came, always scarce and necessary, and it was wet for several days. No problems.

And here is a series, just for fun, because pigeons and birds came out.

Strengths and weaknesses

The antenna is directional (not directive), i.e. you cannot point it at another continent and listen to it as you would with a multi-element directive, but you can rotate it to reduce interference from nearby electronics and other noise.

It is much cheaper, handier, smaller and more discreet than other antennas of this type, making it ideal for installation in confined spaces or where there is no access to the roof, and you can always mount it on a temporary stand and store it after use.

Also, as it takes up very little space when disassembled, you can take it with you on an excursion to hang it from a tree, a fence or any other natural or improvised mast.

It is an antenna, it does not work miracles, but there is no denying that it has a surprising performance in bad conditions for a very low price if we compare it with other antennas of this type, ten times more expensive, such as the Wellbroock ALA1530LNP, mythical antenna that stopped being manufactured at the end of April 2023 as the company closed due to retirement.

But it is not all virtues.

Its amplification is a double-edged sword, on the one hand the reception boost is noticeable, but on the other hand it is accompanied by a lot of noise. Curiously, the reception quality can be improved by lowering the gain and playing with the filters.

Another negative point is the cable, which is not only fixed, but also very thin and prone to noise. With a more shielded and thicker one, like an RG213, this antenna receives much better. Fortunately, if you are not too clumsy, you can always modify it and add, for example, a BNC connector, so you can put a longer run of cable in it without having to resort to splicing connectors, with the consequent loss of reception.

And if you are an expert handyman, you can always make other advanced modifications, such as adding a more powerful ring.

One improvement you can try is to turn up the potentiometer inside the box (making sure to reseal the box if you are leaving it outside) which will increase its gain and improve reception but also increase the background noise level. By playing with the gain, you can try to achieve the optimum signal-to-noise ratio.

It is important to know that turning the potentiometer clockwise decreases the gain and counterclockwise increases it.

Listening, some recordings

As soon as I switch the receiver on, I get an idea of what I'm going to hear from the location and orientation. I mainly receive stations from the northwest. Thus, the transmissions between operators from Jaén, Zaragoza, Valencia, Catalunya and from France, Italy, United Kingdom, Germany, Poland, Bulgaria, Serbia, Croatia, etc., but also from Russia, predominate. Although, depending on the propagation, the signal has also arrived from some stations further south.

A couple of minutes of R7ET, Sergej, from Cherkesk, Russia on 7131 MHz

The antenna has a very good shortwave performance and every night you can listen to different international stations with Spanish broadcasts in different time slots.

It also performs very well on 40 and 20 metres. I have even been able to listen to some stations from different continents on 80 metres, as well as on 10 and 11 metres (CB), where I have been surprised to hear many national and central European stations, but especially from Eastern Europe, in quite decent conditions.

Almost every night I hear Blagomir, YU1XA, from Serbia, which I'm sure comes with good antennas and not a few watts, loud and clear on 40 meters at some point.

Here are a few listens with the antenna just mounted and with poor propagation conditions (the recording does not do justice to the real audio quality with filters and headphones).

Radio China International, always very strong at night, like Radio Romania International, TRT Turkey and others.

The mythical diexist henhouse of the popularly known "triple 5", the call-in channel on 27.555 USB, where it is rare the day that there is not some brawl.

Station EA5FHC (Mislata, Valencia) in competition on 7199 MHz

On 11.253MHz USB there is a Volmet (French acronym for vol, "flight", and météo, "meteorology") operated by the British Royal Air Force at St. Eval on the north coast of Cornwall, broadcasting 24 hours, callsign "MKL" and also known locally as "Military One".

It broadcasts 24-hour voice weather data such as wind speed, temperature, etc. so that aircraft in flight can obtain this information.

Three minutes of RAF VOLMET (UK) on 11.253 MHz USB

is eavesdropping legal?

Yes, as far as I know, or as far as I remember, no licence or legal process is required to be a listener, as long as you are not using a transceiver, i.e. equipment capable of transmitting on those bands that require authorisation and a licence.

Now, if you don't have any radio licence, but you want to practice diexing and be able to send QSL cards and reception reports for which you need a SWL callsign, you can apply for one at swarl.org and you get a kind of "certificate" like this one with a classic diploma style.

This callsign they give you will become part of their membership list and has no validity other than to certify that you have joined this international group of listeners because you are interested in radio stuff.

You can also do the same and apply for a WSL callsign in its Spanish version from FEDI-EA, Federación Digital EA.