MLA-30, any good for anything?

Back in August I read about MLA-30 a (very) cheap active loop antenna that was said to be at least a good one, if not even as good as the more expensive “original” loops.

I wanted to test how well it might perform here at my city home in the middle of huge QRM and no place for long wire antennas. I got one from eBay with only 37€ (including p&p) so it was cheap enough to test without spending some 300+ € just to find out that it won’t work well where I’m planning to use it.

The kit was like “Plug & Play”, all you need to get started with springy like loop, all the cables and the power supply unit. What you need to provide yourself is some kind of support for the loop as it is very wobbly and will not stay upright by itself.

MegaLoop MLA-30

It took much longer to arrive than I expected. I ordered the MLA-30 from The Netherlands thinking that it will be quick delivery inside EU (to Finland), but instead of like one week I waited three weeks – well, I have all the time 🙂

All the parts needed for the antenna arrived in good shape

For the temporary support I used camera tripod, some velcro and wooden stick to get the loop up and turnable. After some tests I found out that I need to position the loop so that it is facing east-west (when looking directly through the loop). By doing this I was able to minimize the huge QRM I have in my city home.

The tests:

It took several days before the ‘radio weather’ was good enough for me to test the loop.

For the benchmark I used my remote site, SRPDuo with Windom wire antenna (40m). The loop was powered by a USB powerbank – perhaps not the best idea due to the way USB powerbanks works – they usually have a Buck&Boost voltage converter that uses some 100-300khz switching frequency. This is not the best way to power sensitive radio device that is meant to be used for listening in the same frequency band, but this was test so i used it anyway.

I used AirSpy Mini as a SDR radio with NooElec HamItUp up-converter as the AirSpy Mini cannot tune under 24Mhz. HamItUp “moves” the lower bands (0-30Mhz) up to 125Mhz so that the radio can hear them (125Mhz = 0 … 155Mhz = 30Mhz).
Software used for testing was Airspy’s own SDR# and the excellent SDR Console.

The loop was indeed very easy to put into action, right away I was able to receive all the “basic stations”. I have no real testing equipment nor enough experience with loop antennas, so I am not the best one to judge but if I can receive some (from my point of view) exotic stations from my city balcony then the loop really works!

The final test was done using some not-so-official stations that usually have very low power, self made equipments and lots of DIY spirit behind them.

For my surprise I was indeed able to receive those stations, sometimes with as good signal as the benchmark system at my remote site.

Benchmark system: SDRUno – RSPDuo – City Windom (40m)
MLA-30 test: SDR Console 3 – AirSpy Mini – HamItUp – MLA-30

31m, 41m, 49m and 75m band’s – comparison:

For reference I took screen captures of some HF bands where it is easy to see how well the MLA-30 loop performs, remember that it is tested against 40 meter long wire antenna and very good quality SDR receiver.

First four pictures are from MLA-30 (with black background) and rest are from City Windom (greyish background).

Final words:

From my experience this kind of cheap loop indeed can be used well with SDR’s. I find it very interesting piece of an antenna especially if you need very light, very small antenna that is very easy to operate and even take with you to your holiday trip!

The All New remote RIG – Part 1.1 “Testing the HF shield”

One problem in my system is that I need to power it using cheap switched-mode power adapters. They are – well, cheap, universal, small, easy to get – and a huge source of wideband HF interference.

The best solution would be to replace all these power supplies with real transformers and linear regulators, but for my project they are way too heavy and big. I need to have 8 different power sources from 5V to 24V and one of the power adaptors needs to be able to communicate with the system itself to automatically choose the power level (USB-C powered SoC computer).

So, there must be some way to – if not totally get rid off – but at least to get the noise level down.

I decided to test if a cheap metal mesh would be enough. I got 60cm x 200cm roll with 0,9mm mesh size with 15 euros.

After few hours (and very painful finger mutilation – oh those spikes!) I had a test “box” that I could use to test if this kind of shield is enough to isolate most of the HF interference these switched-mode power adapter causes.

I covered a table with the metal mesh, then used empty wine bottle as an support for small loop-antenna. The antenna was connected via DownConverter to AirSpy Mini so that I can see what happens down there in HF (VLF) range.

From the power adapters I have I selected the most noisy one for this test. A halogen lamp was used for the load and the power adapter was placed so that is was directly under the loop-antenna – approx. 30cm from the antenna.

The software I used for measuring was SpectrumSpy, really simple yet powerful small software that comes with SDR# that can be used to monitor large block of spectrum at once. It only draws the waterfall, so no sound is extracted from the radio.

Test results – were AWESOME!

Yes yes, I know that this is the basic Faraday’s cage -sort of, but still I was very surprised about how well it was able to ‘clean the band’.

Here is 10MHz wide band starting from 0Hz ending at 10MHz. Note that because of the DownConverter the scale in the picture is +125MHz higher than the actual tuned frequency, so 125MHz = 0Hz and 135MHz = 10MHz.

Time to hide the power supply just by placing the cage cover over it. Note that there is no grounding whatsoever in this system, just a metal mesh on wooden table. Look at that iPad screen – Wow! Just covering the power supply, no grounding of the mesh and huge difference!

This was so promising that I wanted to take the test one step further and create a very AdHoc grounding for the metal mesh to see if it helps at all … and it did.

This is the SpectrumSpy view of 0Hz – 10MHz with me ‘grounding’ the mesh with my both hands – is this perhaps called “The nerding of the mesh?” 🙂

This was indeed something I did not expected to see. Just 30cm above the veeeeery noisy power supply and the whole band is almost clear.

Here is the same in one picture, the mesh cover removed and then put back with grounding (me).

Yes, oh yes – I think I found a solution to get rid of most of the HF interference caused by these yet wonderful but also very noisy power supplies.

Time to create a full cage with all power supplies … more painful finger prickling 🙂