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Technical Topics => Equipment => Topic started by: Matt285 on October 21, 2019, 1149 UTC

Title: MLA-30 Loop antenna
Post by: Matt285 on October 21, 2019, 1149 UTC: Please let me know about your experiences with the MLA-30 antenna. I've seen a lot of positive reviews so far, but would love to hear first hand opinions.
Title: Re: MLA-30 Loop antenna
Post by: Matt285 on October 22, 2019, 0013 UTC: Im having trouble copying a link for some reason. 'Youtube' MLA-30 VS W6LVP loop.
Title: Re: MLA-30 Loop antenna
Post by: JimIO on October 22, 2019, 0228 UTC: https://www.youtube.com/watch?v=LgSnmXE0n0E Works for me.

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Title: Re: MLA-30 Loop antenna
Post by: Matt285 on October 22, 2019, 1257 UTC: Thanks for posting the link.
Title: Re: MLA-30 Loop antenna
Post by: NJQA on October 23, 2019, 1205 UTC: The schematic was reverse engineered here:

https://www.g8jnj.net/activeantennas.htm#MLA30

I haven’t been that impressed by it other than the low price. The “power isolator” actually has an inverter in it to raise the 5 volts up to something higher. I question the wisdom of putting a switching noise generator there!

I might try it with a conventional power isolator at 12 volts to see if it works any better.
Title: Re: MLA-30 Loop antenna
Post by: Matt285 on October 24, 2019, 0025 UTC: I find it amazing that no one on this whole forum owns one of these antennas. I have received several emails now from first hand purchasers who are very pleased with the product. Yes, i'm sure that it has some faults if you look for them hard enough, but I feel like most have nothing to say because their just lurkers without any opinion or they've already purchased a Wellbrook or W6LVP and can't bare the fact that they paid 10 times more for what they got in comparison to a product that is much more affordable. Its a shame that people can't get off their high horse and admit that there is an affordable option that would greater their listening experience.
Title: Re: MLA-30 Loop antenna
Post by: NJQA on October 24, 2019, 1134 UTC: I have one. And I also have a Wellbrook. I haven’t given it a thumbs up or thumbs down because I haven’t compared them side by side, in the same location. My initial impression is that it seems noisy, but that was with it inside the house, so you can’t draw conclusions yet.

But my comments still stand. The price is low. And I don’t like their approach to providing power. Putting a switcher right at the bias-t is nuts. My own unit started having problems with the LED intermittently operating. The schematic showed it is driven directly off of the switcher, so I suspect the switcher has failed.

There are a lot of choices out there for loop antennas - Wellbrook, DXE, Pixel, MFJ, and W6LVP to name a few. The price for these tend to run in the $250 to 450 range. For that money you get a huge step up in both the electronics and in the mechanical construction.

Everything about the MLA30 is cheap. To sell at a $30 price point it has to be. I seriously doubt it would last more than a year or two exposed to the weather. If you look at G8JNJ’s posting, you can see that the circuit has some serious design mistakes. I fully expect that the parts inside the unit are chinese counterfeits. They would have to be at this price point. I suspect the plastic enclosure will turn brittle when exposed to sunlight. This is not something built for the long term.

That being said, there are uses for a $30 antenna, so it has its niche. Just realize it isn’t in the same class as the other loops. It may be good enough for your particular situation. Or not.
Title: Re: MLA-30 Loop antenna
Post by: ChrisSmolinski on October 24, 2019, 1311 UTC: While I do not own an MLA-30, nor a Wellbrook, from the posts I have seen about them (the SDR-Radio mailing list recently had an excruciatingly long thread) by those who have used and compared them, the MLA-30 is not comparable to either a Wellbrook or LZ1AQ loop. Even without testing them, basic economics suggests this is going to be the case.

That's not to say that the MLA-30 or W6LVP may not be useful for some DXers. Maybe they were using the whip antenna on the radio or a random piece of wire laying on the floor in the shack previously. An inexpensive active loop is likely to be better than that, especially if it is now outside. To a large extent the antenna(s) to use depends on your location and situation. You may not have the room for a larger/better antenna. Many DXers unfortunately live in high RFI environments. If your noise floor is huge, it probably does not matter what you use for an antenna.

I am fortunate to live in an RF quiet rural area, with enough land for large, full sized, passive antennas. I did have an LZ1AQ based loop for some time and was impressed with the performance for the size of the antenna. But it does not come close to the performance of my full sized passive antennas, nor do I expect it would for anyone who is not noise floor limited. That's why I never bought a Wellbrook, Pixel, or similar high-end loop, they won't be of any use for me. FWIW the loop in question now functions as a passive loop (I have sensitive enough SDRs that I can make use if it that way) and it is useful in some situations such as on MW where the directivity is a benefit.
Title: Re: MLA-30 Loop antenna
Post by: Ray Lalleu on October 24, 2019, 2052 UTC: Quote from: NJQA on October 24, 2019, 1134 UTC

I suspect the plastic enclosure will turn brittle when exposed to sunlight.

Just give it one or two coats of paint. (A general idea for any plastic part not intended for outdoor use)
Title: Re: MLA-30 Loop antenna
Post by: Josh on October 24, 2019, 2129 UTC: I was looking at one for a few months now and was undecided between it and the parts kit W6 loop, if they put a switcher in the feed, no way, this is rfi-ing your anti-rfi antenna by design. When you have a linear dc psu you might get 60cps or 120cps ripple, but not much else unless it's very poorly designed or sickly, but with a switcher you get harmonics ewevery 16-100kc or so thru hf.

I wonder if Smolinksi Heavy Industries will ever roll out a diy active loop, say just the feed block and head unit, user supplies/builds loop element and coax, with the head unit having decent sn and dynamic range.
Title: Re: MLA-30 Loop antenna
Post by: Matt285 on October 24, 2019, 2312 UTC: In hindsight I realize my post was a bit accusatory and aggressive. The biggest thing I wanted to get out was that why can't we embrace more affordable ways of bettering our hobby in particular, not just for the people that have been involved for many years, but for the people that are new to it. We all have the same goal of keeping this alive. Yes as I said in reference to the MLA-30 .There are no perfect products(especially the cheap ones) but I love the feedback negative or otherwise. Its all about starting a talking point. Lets put our brains together and find a way to improve such products. There are so many great minds in this community. I would also like to say that a big part of my discouragement is due to seeing so many empty comments vs the views. yes Ive done this for a long time, but just because a newer person post a comment about a catch we've gotten many times, it doesn't mean that we need to ignore them. Let's be more encouraging to these people. Most all of us remember the magic of our first 'cool' catch. It only takes a few key strokes to acknowledge them of their strides of listening for hours to experience that joy. Don't just ignore post because they may seem mundane . Take a minute and expound and give tips. It goes a long ways
Title: Re: MLA-30 Loop antenna
Post by: jasmine on October 27, 2019, 0554 UTC: Quote from: IZS4 on October 21, 2019, 1149 UTC
Please let me know about your experiences with the MLA-30 antenna. I've seen a lot of positive reviews so far, but would love to hear first hand opinions.

hi, though i am new at this hobby i've gotten pretty good results it seems with the MLA-30. i'm a college student so space was at a premium when thinking about antennas (previously i had an indoor longwire lol). anyway i was looking into loops and decided to give the MLA-30 a try as it was in my budget range.

anyone can look at my loggings in the Utility forum to see some of my results with it from my Seattle, WA location.
Title: Re: MLA-30 Loop antenna
Post by: Josh on October 27, 2019, 2207 UTC: See? It works well enough. However, it could be better if they got rid of the switcher and allowed perhaps some gain adjustment, or tuned the chip to increase dynamic range. As I recall in one test it beat the other loop as it could null deeper, wich in some cases is why people buy or make loops to begin with. If it's Jasmine approved it's good enough for me.
Title: Re: MLA-30 Loop antenna
Post by: Matt285 on October 27, 2019, 2331 UTC: Im not sure how accurate it is, but I've heard the deeper nulling is due to using a thinner wire. I'm gonna get one for sure. If nothing else it should be a great portable antenna for easy set up. It will be a few weeks since I had to shell out for $140.00 on Halloween costumes. (3 Kids) I will definitely post the results and comparison to my 135' OCF dipole.
Title: Re: MLA-30 Loop antenna
Post by: ChrisSmolinski on October 28, 2019, 1014 UTC: Quote from: IZS4 on October 27, 2019, 2331 UTC
It will be a few weeks since I had to shell out for $140.00 on Halloween costumes. (3 Kids)

You should have bought a loop antenna for each of them to wear as part of a robot costume.
Title: Re: MLA-30 Loop antenna
Post by: Jim Bee on November 09, 2019, 1458 UTC: I sent my MLA-30 back because it could hardly receive any stations on medium wave
Title: Re: MLA-30 Loop antenna
Post by: Matt285 on November 09, 2019, 1836 UTC: Thanks for the feedback. I haven't heard anything in regards to that portion of the spectrum.
Title: Re: MLA-30 Loop antenna
Post by: Josh on November 19, 2019, 1926 UTC: Comparing Four Wideband Magnetic Loop Antennas on HF
Over on YouTube the Scanner and Sdr Radio channel has uploaded a video comparing four different brands of HF wideband loop antennas using an SDRplay RSPduo. The loops he tested include the cheap Chinese MLA-30 (~$40), the Cross Country Wireless (CCW) loop ($70), Bonito ML200 (~$442) and the Wellbrook 1530LN (~$305).
https://www.rtl-sdr.com/comparing-four-wideband-magnetic-loop-antennas-on-hf-with-an-sdrplay-rspduo/
Title: Re: MLA-30 Loop antenna
Post by: Treehouse SWL on November 19, 2019, 2133 UTC: Based on Jasmine's results not too far away from where I listen, and the fact that I've seen other overall good reviews of the antenna, I'm getting an MLA-30 as soon as we can move back into our regular house and I can settle in again at my usual listening post there.

I go in with the expectation that it probably won't perform as well as the expensive loops, but for a technically challenged DXer like me who can't easily build his own loop and who also has to feed three kids and pay a Seattle-area-sized mortgage, it seems worth a shot!
Title: Re: MLA-30 Loop antenna
Post by: Josh on November 20, 2019, 2352 UTC: After watching the vid, pretty sure a MLA is going up. That is unless Smolinksi Heavy Industries rolls out a loop and has me alpha test it.
Title: Re: MLA-30 Loop antenna
Post by: JimIO on November 21, 2019, 0335 UTC: Found a place in NJ that sells them. Mine should be here by Dec 4. 8)

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Title: Re: MLA-30 Loop antenna
Post by: Matt285 on November 23, 2019, 1641 UTC: Awesome. I have to wait until Christmas for mine. Im looking forward to all the feedback on how the antenna can be improved, although with all the components being encased in epoxy it may be tough. I have complete faith in you guys though to come up with new ideas. Im also down for Chris to come out with a kit or finished product of a similar antenna. I have no doubt he could make it happen. Josh will be held accountable also of course.
Title: Re: MLA-30 Loop antenna
Post by: Josh on November 23, 2019, 2341 UTC: Lol! Anyway it woulda been nice if the guy what made the vid tests coulda mentioned how long he made the loop replacing the stock MLA loop. I assume he made it identical to the rest to even the playing field.
Title: Re: MLA-30 Loop antenna
Post by: Matt285 on November 24, 2019, 1431 UTC: Assuming your talking about a Youtube video. Did you try leaving the question of measurement in the comments or possibly some type of direct message? If your able to. Provide a link for the particular video. Thanks
Title: Re: MLA-30 Loop antenna
Post by: Josh on November 25, 2019, 2149 UTC: https://www.youtube.com/watch?v=FRhDHHpLoaM&feature=emb_title

"Comparing the MLA-30, Cross Country wireless, Bonito ML200, and the Wellbrook 1530LN magnetic loops on HF the length of the wire used on the ccw, mla30 and the bonito is 5m and not the diameter of the loop which will be approx 1.6m"

" Les Norton G4JNW
1 week ago
Would have liked to have seen a comparison with a Wellbrook ALA-100 as thats meant for wire rather than the 1530LN is a fixed loop that way you could have tried the same length, the CCW is meant to have 3m wire too so a better comparison would have been 3m with all. Just a thought

Scanner and Sdr Radio
1 week ago
Hi Les I have had some time with all the loops and tried different lengths of wire for the loops 1m, 3m and 5m (wire length not the diameter of loop) the results across the bands on hf were all similar whichever length of wire loop I used, the difference was that the longer the wire the better each loop performed at LF but the actual noise snr etc was pretty much identical as in the comparisons, as the video was already long I did not show the comparisons with the shorter lengths of wire as it did not show anything differant if it had it would of been included "
Title: Re: MLA-30 Loop antenna
Post by: ChrisSmolinski on November 25, 2019, 2157 UTC: Quote from: Josh on November 20, 2019, 2352 UTC
After watching the vid, pretty sure a MLA is going up. That is unless Smolinksi Heavy Industries rolls out a loop and has me alpha test it.

Sorry... I'm too busy at the moment planning the installation of a 120 ft T2FD antenna. :)

I did have an LZ1AQ amplifier on the crossed parallel loop for a while. I since removed the amp and found that many SDRs (AFE822x for example) have enough sensitivity that they can use the loop passively. Maybe something people want to consider - build a large enough loop and you don't need an amp and all the associated problems that come along for the ride. The crossed parallel loop is 2m x 2m, made of four 1m square loops. Quite directional on MW and LW, not on HF but then loops rarely are.
Title: Re: MLA-30 Loop antenna
Post by: Josh on November 25, 2019, 2226 UTC: Is there s schematic of this crossed thingy you speak of?
Title: Re: MLA-30 Loop antenna
Post by: ChrisSmolinski on November 25, 2019, 2229 UTC: Quote from: Josh on November 25, 2019, 2226 UTC
Is there s schematic of this crossed thingy you speak of?

There's a post right here in the Equipment forum, along with a link to my blog post with construction details.
Title: Re: MLA-30 Loop antenna
Post by: Matt285 on November 26, 2019, 1858 UTC: I had posted on the equipment forum about an adapter for hooking up a MLA-30 to a standard portable receiver such as a PL-660,880, Grundig G5 etc. Josh posted a question about overloading this type of rig and it made me think. I have seen a few videos posted using the MLA-30 with these type of rig without a noticeable issue. Any thought?
Title: Re: MLA-30 Loop antenna
Post by: chanito on December 02, 2019, 1513 UTC: Just got mine Friday. It's a $30 antenna. It is not something I would put outside unless inside a weatherproof enclosure. I tried it for a bit connected directly to a RSP1A to exclude the potential for USB power noise from the power injector. Hanging in a closet on the second floor, it picks up all the noise just like any other antenna indoors at this locale.

See comparison with Sigma 18' HF vertical and a $600 widebanded Belar LP-1A shielded amplified MW loop. Ignore the S meter as it is showing what the radio is actually tuned to, so we'll use the scale on the left as reference. Radio is the RSP1A with the AM/FM notch filter ON because of 1350kHz station about a mile away.

If you look at signal peaks, on MW you can see it is about 6dB down on local station 1350kHz, and about 11dB down at 7490kHz compared to the vertical, and to give a fair comparison on MW, only about 6dB down at 1350kHz from the commercial MW Belar loop located in the same room, both oriented E/W.

MLA-30
(https://i.imgur.com/6On4b32.png)
Vert
(https://i.imgur.com/dkdVqtL.png)
Belar
(https://i.imgur.com/3BSpQGO.png)
Title: Re: MLA-30 Loop antenna
Post by: Matt285 on December 19, 2019, 0045 UTC: Has anyone else received their new MLA-30 loop? I have to wait until mid Jan. Please post any reviews or findings. Thanks
Title: Re: MLA-30 Loop antenna
Post by: JimIO on December 19, 2019, 0430 UTC: I had mine for a couple of weeks. Nothing to report due to crappy weather.
Next Tuesday: Mostly sunny, with a high near 45. Calm wind. Maybe after then.

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Title: Re: MLA-30 Loop antenna
Post by: chanito on December 29, 2019, 1936 UTC: This configuration works remarkably well, and it is directional enough now to kill some local noise that was plaguing reception. Self supporting as well.

(https://i.imgur.com/MNq7D9o.jpg)
Title: Re: MLA-30 Loop antenna
Post by: Matt285 on December 29, 2019, 2349 UTC: Thanks for the reply. I see you have configured the loop in a non traditional way. Interesting. Let us know what you've come up with there.
Title: Re: MLA-30 Loop antenna
Post by: Matt285 on December 29, 2019, 2356 UTC: After hitting submit I realized you did speak about the configuration. Is that the wire that came with it, broken into two smaller loops or did you add new wire? Thanks
Title: Re: MLA-30 Loop antenna
Post by: chanito on December 30, 2019, 1553 UTC: It's the wire that came with it, and it is still in one piece, just rolled into two turns then spread out.
Title: Re: MLA-30 Loop antenna
Post by: Josh on December 30, 2019, 2208 UTC: I recall reading in the teardown/review that the input of the guts is looking for something on the order of 100 ohms, so a loop that had that z at hf would likely perform best.
Title: Re: MLA-30 Loop antenna- new life
Post by: kris on January 10, 2020, 1720 UTC: Hi -IZS4 pleasantly asked about experience with MLA30, and I will add my pebble to this construction.
I've created a new life for this antenna! But in turn, maybe I will inspire some of you to act.
I bought it straight from China for 35 USD, not knowing many materials about it yet.
From the beginning I was going to improve it. Here are my comments and experience in cooperation with the SDR-FL-Play receiver:
- 63mm diameter loop (203cm circumference 1mm stainless wire) good for holiday trips.
This is low and the expected low signal level was confirmed by tests.
In the MW range only the strongest stations were received, in the LW range the Polish Radio 225kHz station was not received from a distance of approx. 250km. The useful signal started from the 49m band and was getting better at the higher ones. The loop showed directional properties in the 49m band.
A potentiometer for adjusting the HF gain is available in the junction box. I have not observed any distortion of the receiver in any position. Its setting should be guided by an acceptable increase in the noise level. It is variable in different bands and it is difficult to find a compromise. The second possibility of adjusting the signal level is through the HF attenuator in the power supply module / splitter - it also affects the noise level and it is difficult to find the "golden mean". It may be a coincidence, but adding a linear amplifier about 10dB before the input of the receiver caused that many signals already on MW became readable, and was more difficult obtainable by adjusting the HF gain and attenuator.
- the antenna is quiet compared to Skyloop, however, the directional properties of the loop sometimes allow better readability.
> The signal level and the shift below the working range increases with the diameter of the loop, but practitioners recommend not exceeding the diameter of 150cm.
I made a new loop with a diameter of 155cm using (495cm) PE / AL layered pipe with a diameter of 16mm. You could already receive from the LW band, but the signal level did not satisfy me with Skyloop outside the window.
What will happen when I tune the MLA to resonance? Parallel to the end of the loop, I turned on a variable capacitor around 730pF.
Disappointment - while tuning the loop, on the HF waterfal I observed a several hundred kHz wide resonance mound, raised only to around 3dB. Where is the good Q, sharp resonance and high signal level described in the literature?
The input of the symmetrical amplifier (about 1kOhm) is preceded by HF pass-through filters (about 100 Ohm). This is a clear construction error of mismatching with very low loop wave resistance - unless it is deliberately done to ensure antenna broadband.
I see this as a deterioration in the resonance properties of the loop.
> I solved this problem by using a coupling loop. I unhooked the MLA from the large loop.
To the MLA connectors I screwed a 30 cm diameter coupling loop made of AL # 3mm wire and mounted it symmetrically against the capacitor.
And a miracle happened! The MLA antenna from the donkey turned into a racing horse!
It tunes sharply with a peak higher by at least 10dB and 50-100kHz wide, so if you tune your antenna too quickly, you may not notice the tuning moment. The receiver (or maybe the MLA amplifier) usually overdrives in the stag signal batch, which requires tuning the antenna from the max signal (I haven't optimized the HF gain and MLA attenuator settings yet).
The antenna now has a clear resonance of around 2.7 to 12 MHz, but also LW and MW are received satisfactorily.
To end my long description, I recommend that you don't have garden for a full-size antenna, put a rebuild MLA-30 outside the window and enjoy listening effectively to the whole world!
P.S. Of course, you can do remote operation of the loop by mechanical or electrical re-tuning and turning.
The symmetrical MLA amplifier requires about 8V for its optimal operation. The designer made life easier for us by supplying typical 5V voltage through a USB socket in the power distributor near the receiver. From here, a coaxial cable to the loop amplifier already has a voltage of 12V. It is stabilized because in the 4-12V range on the input side the output voltage does not change and it does not affect the level of gain and noise.
You can confidently reduce the MLA noise level by introducing 12V voltage from a classic power supply to the antenna cable outside the 5 / 12V converter.
Title: Re: MLA-30 Loop antenna
Post by: Matt285 on January 12, 2020, 1635 UTC: Kris, Thank you so much for your detailed review and advise on the MLA-30. Mine is currently on its way to my house. I will post my findings and modify as needed. Luckily I already ordered an an adapter for my Grundig G3 (Thanks for the link Chanito ) i will have to get a SO239 adapter to use my Icom receiver.
Title: Re: MLA-30 Loop antenna
Post by: Matt285 on January 12, 2020, 2008 UTC: First plan is to add a BNC connector at the box so that I can use different coax. I also plan to seal the outside box better if I decide to use it in a full time outdoor setting. Looking forward to experimenting with it. for $43.00 I don't have to much to lose. Even if its just an upgrade for my portable, its money well spent.
Title: Re: MLA-30 Loop antenna
Post by: Matt285 on January 13, 2020, 2343 UTC: So the MLA-30 arrived this evening. I was able to put it up in a temporary way on a piece of PVC I use for QRP portable ops. It will be hard for most people outside of the southeast to fathom, but Mosquito's were eating me alive. I hooked it up to my Grundig G3. Received several stations from Europe and South America, WWV,CHU etc along with activity on the ham bands. I only got to play with it for 15 mins, but I will say it made the Grundig come to life. Worst case scenario it will be a great antenna for portable ops with the grundig and will also be great when I get an SDR receiver running on the laptop to scan the ham bands when im portable. Sometime this week I will order an SO239 adapter for the Icom and do some more testing. I'll keep you posted. Bottom line so far. $41.00 USD well spent.
Title: Re: MLA-30 Loop antenna
Post by: chanito on January 14, 2020, 0113 UTC: Kris' info is interesting to me. Upping the voltage to 8vdc is something I'll attempt. My particular MLA-30 circuit board seems to be completely potted, so adjustment will be challenging. The conversion of the MLA-30 to a magnetic loop config is a cool hack.
Title: Re: MLA-30 Loop antenna
Post by: Matt285 on January 14, 2020, 0213 UTC: For sure. And if something goes wrong, its not like you blew up a Wellbrook. Look forward to any insights.
Title: Re: MLA-30 Loop antenna
Post by: Matt285 on January 14, 2020, 1743 UTC: Kris, If possible. Could you post a couple of photos? Thanks
Title: Re: MLA-30 Loop antenna
Post by: cj468 on January 14, 2020, 1903 UTC: I got one of these over Christmas and had a little play with it, mostly on the ham bands. Generally it seems an improvement over the random length long wire I also have, although sometimes the noise increase with MLA means the longwire gives a clearer signal even if not as strong. Only got the display on the XHData as a signal meter but that and my ears seems to indicate the MLA gives stronger reception.

I'd also be interested in seeing a couple of pictures of Kris's mod, especially if it can be done by an "electronics novice" with basic/minimal soldering skill. A few posts on youtube and other forums suggest replacing the coax, as IZS4 also suggests, so maybe I'll try that too.
Title: Re: MLA-30 Loop antenna
Post by: Josh on January 14, 2020, 2130 UTC: Depending on the current draw, I'd be interested in running it on a battery, right at the antenna, with a small solar panel to charge with.
Title: Re: MLA-30 Loop antenna
Post by: Matt285 on January 15, 2020, 0027 UTC: For my trial run I used a small battery with a USB port. Basically it's a back up battery for extended charge with cell phones or other devices. Can't think of anything better. At first iIwas going to use a small battery I use for QRP portable ops with a cig lighter type adaptor to lower the voltage to standard USB voltage. I still would if I planned on using on a camping trip or longer outing. Looking forward to playing with it more this weekend. I would like to try the 'Chanito' style double loop as well. Interesting idea and self supporting on a flat surface!
Title: Re: MLA-30 Loop antenna
Post by: Matt285 on January 15, 2020, 1906 UTC: Update on the small battery use. I have to test with another unit to confirm if the one im currently using is bad, but I noticed the battery unit powers off after a couple of mins and has to be reset. I will use a small 12 volt battery with USB adapter next.
Title: Re: MLA-30 Loop antenna
Post by: kris on January 18, 2020, 2130 UTC: Hi everyone, thanks for your interest, it's worth tinkering with.
My technical adaptations use common knowledge described on the web, but I will add some details:
(https://i.imgur.com/EkdbXqB.jpg?3)

- the MLA box is solidly made of white ABS and has 4mm thick walls, so it won't deform easily or crack quickly. Colleague Ray rightly suggested to protect the material against UV degradation by spraying with varnish.
(https://i.imgur.com/YzTfZjTm.jpg)
- the lid of the box is solid and has a channel with a well-fitted gasket, but the cable passes through the opening in the box without a sealing gland. There is enough space to fill a BNC, F / TV or SMA socket tightly. The socket can be easily soldered to the cable inserted into the amplifier board, without interfering with the board, it is flooded with black hard resin (probably epoxy) and the gouging will result in tearing off the elements and damaging the board.
(https://i.imgur.com/OAnbMB3m.jpg)
- the loop is screwed through M-4 (stainless) screws through the box walls. In my opinion, it is worth sealing with epoxy resin, and on the outside of the box put (stainless, epoxy) washers to strengthen the mechanical connection with the loop. A large loop under wind pressure can exert considerable force on the box, and the box transfers it to the pole supporting the antenna.
(https://i.imgur.com/gSXQm1Dm.jpg)
- I have 3mm thick Ag / AL wire and I wanted to make a new loop larger than the original one. I had to slide it into a PE / AL layered pipe to shield against electrical interference from industrial interference signals.
I searched my apartment for the source of interference using the original MLA loop. It turned out that the TV, cable tuner, router, power supplies, computer, lighting and neighbors do not sow them into the environment (at a noticeable level).
In this situation I gave up shielding the loop and made a large loop from the pipe.
Both ends of the pipe, about 3 cm long, must be flattened by crushing and then bent 90 degrees to allow it to be screwed to the MLA box. The aluminum layer is thin and breaks when bent, so the bend must be made on a flat length before you remove the PE layer. It is best to remove the insulating PE coating (about 2 cm) with a hot tip of the (large) soldering iron. Now drill holes for screwing the box. Screw the loop through the washers to ensure good electrical contact with the pipe surface and strengthen the connection.
- as I described in the previous post, the antenna works great if the large loop is tuned to resonance with a variable capacitor (or varikap), and the MLA amplifier box is connected to a small coupling loop (1 / 5D). The signal strength (and noise increase) is so high that it requires optimization of gain and attenuator - both blue potentiometers are visible in the pictures.
It is possible that even better results will be achieved by optimizing the degree of coupling of a small loop with a large one, but I haven't had time for it yet.
- DC 12V stabilized voltage is fed to the MLA amplifier with an antenna cable. There on the plate it is probably reduced to 8V resistors which is optimal for a well-integrated differential amplifier. I advise against gouging in resin - experiment safely with the voltage supplied through the cable.
- In the "Biasing Tee" box you can safely gouge: increase the capacity of electrolytic capacitors, bypass the DC 5 / 12V converter, change the USB power socket and SMA sockets connecting to the antenna and receiver.
(https://i.imgur.com/FodO3r7m.jpg)
- I use a widely available, convenient and good for HF coaxial cable type RG6. I use SMA / F or SMA / BNC adapter connectors, sockets, plugs and F connectors for TV installations, as required.
Good luck and write about your experience!

For the record, here is the schematic diagram of the MLA-30 system
https://www.g8jnj.net/activeantennas.htm#MLA30 (https://www.g8jnj.net/activeantennas.htm#MLA30)
Title: Re: MLA-30 Loop antenna
Post by: kris on January 20, 2020, 1605 UTC: Quote from: Jim Bee on November 09, 2019, 1458 UTC
I sent my MLA-30 back because it could hardly receive any stations on medium wave
You did not hurry with the return. You had to take the wire about twice as long as the original loop. If you don't have free space, fold it up to form two scrolls. The loop diameter will be like the original, and you would lower the reception range to the MW band. You could also tune this loop to the MW range by adding a solid capacitor. The signal level will increase and the received bandwidth will probably be satisfactory, because the goodness of this circuit with the MLA connected is small.
In the first days of using my MLA, I had a surprising glitch. For no reason at all, the antenna became very deaf. Moving the SMA plug on Bias Tee, I found that there is a fault in this place. It was not a bad soldering. In the plug I found an almost invisible thin brass hair left from the thread tapping. He sometimes made a short circuit between the plug nut and the middle pin of the plug. After removing this surprise, the reception returned to normal. It was good that it was in the cable to the receiver and not to the antenna, because I would have a DC short circuit and the ruin of the MLA undertaking.
- - I thought about winding my "huge" loop of PE / AL pipe in two turns. I will try to see if performance will get too bad. The large loop is now susceptible to wind, takes up a lot of space - it is difficult to turn it and hide it in the bush from the eyes of neighbors.
Title: Re: MLA-30 Loop antenna
Post by: Matt285 on January 20, 2020, 2027 UTC: Kris, Thank for posting your detailed photos. I haven't gotten to mess with my MLA-30 much, but I can say its a great improvement for my Grundig G3. I haven't run it through it's courses, but it definitely shows directional properties on higher bands such as 20m (14 mhz) and even a small bit on 10 mhz WWV. I will try a different type of loop at some point, but I'm happy with it for what it cost.
Title: Re: MLA-30 Loop antenna
Post by: Josh on January 22, 2020, 0659 UTC: Just saw this vid on the subject;
https://www.youtube.com/watch?v=RvXsywLbi9k
https://www.youtube.com/watch?v=FRhDHHpLoaM

the mla seems to be pretty fair for the price, and with Kris mod of lengthening the loop it might be a better showing on vlf
Title: Re: MLA-30 Loop antenna
Post by: Matt285 on February 01, 2020, 1407 UTC: After some various testing, my current conclusion with the MLA-30 is that it is well worth the $43.00 I spent on it, but I don't plan on mounting it permanently for a secondary antenna outside. I plan on drilling out the sides to make a firm 1/2'' PVC loop and make a small PVC stand for portable ops with my Grundig G3. If you are use to running a telescoping whip or small piece of wire this antenna will make your portable rig come to life and it definitely shows directional properties on frequencies above 10mhz, but my 135' OCF dipole seems to steal the show. It will also be perfect for running with an SDR receiver in the field while doing QRP portable ops to see whats going on on 10,12,15,17 and 20 meters. Again no regrets and I would suggest purchasing one to try it out. Maybe when I have some more time I will try some of the mods I've seen.
Title: Re: MLA-30 Loop antenna
Post by: Matt285 on February 25, 2020, 2205 UTC: So I ended up installing the MLA-30 on the roof semi permanent. Now I can do a bit more side by comparison. I don't have much scientific data to report, but again I must say im very pleased with it. If I didnt have room for a large dipole it would really be a god send. Im now using the Bias T on the RSP2 to power it. Hope to do some more testing tonight on various frequencies. I'll post what I come up with.
Title: Re: MLA-30 Loop antenna
Post by: ultravista on February 26, 2020, 0120 UTC: Have you replaced the SMA connecter on the antenna box and added a longer wire loop?
Title: Re: MLA-30 Loop antenna
Post by: Matt285 on February 26, 2020, 1216 UTC: I do plan on adding a BNC connector and better coax. Haven't thought much about going with a larger loop, but i'd like to rebuild the loop a bit better.
Title: Re: MLA-30 Loop antenna
Post by: kris on February 28, 2020, 2147 UTC: And I wound my large loop of 155cm in diameter into two turns. Now the diameter is 79cm.
The tuning range with the 750pF variable capacitor remained unchanged from 2.5 - 15.5MHz. From the bottom to about 10MHz, antenna performance seems to remain the same as for a large loop. The loop maintains a clear directional characteristic. Above - it tunes less sharply than before and gives a weaker signal. I am disappointed with the high noise level of the loop antenna compared to Sky Loop. I get a similar signal level, but readability is lost in the noise.
Maybe my neighborhood isn't as clean as I thought. I need to remotely tune and rotate the loop and set it aside about 6 m from the house. Maybe it will be quieter than on my balcony - without it,
it makes no sense to use.
Title: Re: MLA-30 Loop antenna
Post by: redhat on June 09, 2020, 0130 UTC: I bought one of these myself to see what all the fuss is about. I'm considering getting a second one to keep in the 'go kit'. I found its performance on medium wave to be acceptable, and the noise is no worse than my existing Chi-town special. That being said, local noise around here is about s7 and the loop seems similar. I may build a bias injector for it and see if any difference in performance is observed. With it I did see WWV on 15, 20, and 25 MHz come in on it the other night, something I've never seen before here with the tune loop.

I will drag it with to a quiet location sometime and see how it behaves in a quiet environment.

+-RH
Title: Re: MLA-30 Loop antenna
Post by: alpard on June 09, 2020, 1033 UTC: I am planning to get one too. It looks actually very interesting active loop antenna for good price.
Title: Re: MLA-30 Loop antenna
Post by: RADIO645 DX Group on September 29, 2022, 2215 UTC: After years of using a 25ft. long wire antenna, I decided to purchase and set up the MLA-30 Mega loop antenna for the Sangean 909X2. Other than having to buy some SMA connectors and the coax plug for the antenna port I'm very happy with the results with MLA30, which exceeded all my expectations. I have since stopped using the long wire and use the MLA30 on both the Sangean and the SDRuno RSP1A. You can't go wrong with the MLA30 in my opinion, despite what the detractors say about the mega loop, it out performs any antenna I've tried for SWLing and you can't beat the price!
Title: Re: MLA-30 Loop antenna
Post by: Kenotic on November 15, 2022, 0534 UTC: I am trying out the MLA 30+ and am having mixed results.

On one hand, some of the stronger stations sound like they're next door! 11780 kHz Brazil is perfect in the late afternoon, as are most of the VOA relays from Africa.

On the other, the noise floor is so high it obliterates anything else. CFRX, Turkey, Radio Educacion? All too much noise now.

Also, if this is supposed to work on MW I'm not seeing any improvement over the internal antenna on my radio.

Any suggestions? Anything I'm missing?
Title: Re: MLA-30 Loop antenna
Post by: RobRich on November 15, 2022, 0958 UTC: The active antenna preamp could be overloading your portable. Are you tuning the lower bands with attenuation enable? Eton probably calls it "local."

How have you deployed the active loop? Inside, outside, height, etc.

Also, does your portable receiver use the external antenna port for MW? Some do not, while others like later Tecsuns require long pressing a key to enable the feature. Not sure about your model as I have not really kept up with Eton receivers in quite awhile.
Title: Re: MLA-30 Loop antenna
Post by: Kenotic on November 16, 2022, 0503 UTC: Thanks for the response.

I'm attenuating as needed -- I can drop it to "local" when it gets to be too much or stations bleed in. For whatever reason Radio Marti likes to go all over the place if I don't.

I've had to keep the loop inside for the most part, but I had it out on the porch tonight. It's mildly better there, some of the weaker signals are fighting through the noise floor. It may take a bit to find a place outside for now consistently. I can't go too high outside right now, but I may try and hoist it up on a PVC pipe I have laying around.

I cannot find any info about a switch to get the antenna to MW, which is a bit disappointing. I'm scouring sites for any hints of hidden features online, but I'm not seeing many.
Title: Re: MLA-30 Loop antenna
Post by: Zoidberg on November 16, 2022, 0830 UTC: Indoor antennas, including magnetic loops or any antenna that touts receiving the magnetic portion of the spectrum tend to be just as vulnerable to RFI as the telescoping whip on a portable or bare random wire to a tabletop receiver. Just the nature of the beast when we're swamped with electronic and electrical noisemakers from every direction.

With any amplified wide spectrum small loop antenna, the best we can hope for is to orient the nulls toward the worst sources of RFI. Sometimes that helps. Often it doesn't when we're surrounded by RFI from every direction.

If you try enough online receivers and SDRs around the globe, you'll encounter some Wellbrook loops and other highly prized loops that have raspy, buzzy RFI just as bad as anything we can get at home with a portable on the whip, or a bit of random wire strung along the ceiling or dangled outside a window. There's nothing magical about a Wellbrook or any loop in an environment plagued by RFI from every direction.

Same with the PA0RDT amplified mini-whips. Those are only as good as the location, and few online tuners have them mounted high enough to be relatively free of RFI. The popular Twente SDR is among the tiny handful that make good use of the design.

Plenty of online tuners and SDRs claim to be in quiet locations, but few actually are quiet. If they've strung up traditional wire antennas -- slopers, dipoles, doesn't matter -- reception is only as good as their nearest worst neighbor. The best, quietest SDRs tend to either be in remote locations, or very directional, such as aimed across the Atlantic or Pacific from either coast, with a few lobes off the backs that make domestic US reception possible. Those are often remarkably quiet because the designs tend to ignore the local RFI. The HFU accessible SDR with 250 foot V-beam aimed across the Atlantic is one such example, being among the quietest in the world of all the SDRs I've tried. But it depends on lobes off the back, small apertures of sensitivity toward US transmitters.

In 15 years in the same apartment battling RFI from neighbors' devices to faulty electrical power sources, to the nearby fire department, I've had the best results from homebrewed passive shielded loop antennas. See: https://swling.com/blog/tag/pixel-shielded-magnetic-receive-only-loop/ and other articles.

None of my radios -- various portables including a Sony ICF-2010, and Palstar R30C sorta-tabletop/portable-ish hybrid -- needs an antenna amplifier. All of them have far more sensitivity than necessary, even on low/attenuated. That includes using the external antenna jack on the Sony, which is only slightly less sensitive than the whip.

Speaking of whips, through trial and error I discovered My Sony ICF-2010 portable is remarkably directional with the whip. Aim the tip of the whip antenna toward the worst local RFI and there's a null. Likewise, orienting the whip horizontally -- parallel with the ground -- is the quietest setting. Also the least sensitive, but it's often easier to actually copy the faint signal with reduced noise.

There are many designs for homebrewed loop antennas, including at least one that doesn't even look like a conventional loop -- the Villard antenna, which is just sheets of aluminum foil mounted on a large sheet of cardboard, plywood, foamcore or gatorboard. The Joe Carr receiving antenna book published in the 1990s includes most of these designs.

These can be tuned by adding a tuning capacitor. Some, like the Villard, and this ugly but functional doodad (https://www.eham.net/article/40484), use overlapping sheets of aluminum foil with non-conductive spacers between the foil -- a sheet of paper, plastic, whatever you have available.

If you don't want to bother with a capacitor, or don't have one handy, too pricey, whatever, you can build the loop to dimensions tuned for the desired band. Optimal reception will be fairly narrow, with good reception possible at other bands scattered across the HF and MW spectrum. With trial and error you can build a very quiet, direction, functional passive shielded loop from nothing but old TV coaxial cable, an adaptor to suit the antenna jack on your receiver, and a place to hang or mount the ugly mess of coax. I used such a fugly loop for years, mounted on the inside of a closet door. The swinging door added directionality to null out the worst local RFI, and I could close the door to hide the antenna from snoopy landlords, maintenance crews and building inspectors who couldn't cite any valid reason not to have an indoor receive-only antenna, but thought there was something suspicious about it. Keep in mind that changing in communications devices have made "radio" a foreign object used only by misfit nerds and spies, as far as most folks are concerned.

Another version that worked even better -- although not an indoor loop -- was a stealth loop fastened to the inside of a wooden fence outside my ground floor apartment window. The loop was nothing but very thin magnet wire, in a roughly square shape, 8 feet along each side, following the dimensions of the fence (I used screws, nails or cup hooks, whatever was handy, to wrap the wire in a large "loop" shape). The wire ends were fastened to an old fashioned TV balun. I ran old TV coax, often scrounged from the dumpster, along the ground next to the building, tucked into the dirt. Then up the wall to a window with the sash cracked open just a bit (thumbscrew sash locks used to discourage burglars), and to the receiver. That loop nulled off the edges (opposite of most small loops, which null off the open faces), effectively nulling out the worst RFI from the parking lot and building lights. Worked great, until the apartment complex maintenance crews found it and tore it down. Which is why I built these from the cheapest materials available. I bought a bunch of magnet wire cheap from the local Radio Shack outlet store years ago. And I scrounged the TV coax and baluns from the dumpster after tenants moved, died or were evicted. So I didn't have more than a couple of dollars sunk into any outdoor passive loop. The only problem with that design now is TV baluns are hardly ever in demand or used anymore. I could use a proper homebrewed balun designed for HF, but the TV baluns worked despite not being optimized for HF.

The best performing versions of my loops were remarkably quiet, enough to reduce local RFI to just above the receiver's built-in noise floor, a sort of white noise low hiss. That enabled leaving the receiver on 24/7 with the volume just high enough to catch the faint sound of a pirate or other signal on 6925, 6955, etc. Rigged to an SDR we could just go by the visual cues onscreen.

The only downside was these passive loops picked up only fairly strong signals, and were more prone to fading. But there was a lot less tiresome RFI.
Title: Re: MLA-30 Loop antenna
Post by: RobRich on November 16, 2022, 1112 UTC: Definitely get the active loop outside away from residential RFI. Do not be too concerned about elevation for now, as vertical loops elevated by least a loop diameter or two tend to not be overly influenced by ground losses.

The MLA-30 is not too directive IIRC, so I would suggest turning it to null local noise if possible and leave it there. Set, forget, and enjoy.

About MW, you might try feeding the external antenna to a few turns of wire wrapped around the portable receiver, thus passively coupling to the portable's internal MW ferrite antenna. I have done similar with outdoor antennas feeding a tuned loop like the Tecsun AN-200 placed next to a portable, too.
Title: Re: MLA-30 Loop antenna
Post by: ChrisSmolinski on November 16, 2022, 1444 UTC: I'll echo the advice to get the loop, or any antenna, outside if possible. Some experimentation may be useful to find the quietest location. Also take care to consider your feedline and possibly add some common mode choking (ferrite cores) to deal with RFI pickup on the coax itself. Remember that CM choking / ferrites only mitigate RFI picked up on the outside part of the shield of the coax. They do *nothing* for RFI/QRM picked up by the antenna itself.

And yes, amplification is rarely needed with HF receivers. That's something for the VHF/UHF bands. All you do, especially with lower cost receivers, is make yourself susceptible to overloading and images. If anything, attenuation might be your friend.

One point to consider about shielded loop antennas is that none of them only receive the magnetic part of the signal - that's either a misunderstanding or marketing snake oil, depending on how charitable you are ;D
Title: Re: MLA-30 Loop antenna
Post by: Zoidberg on November 17, 2022, 0110 UTC: Ditto, tricks to reduce common mode noise picked up by the coax feed line itself.

Even cheaper than ferrite cores -- if your feedline is long enough, just wrap it neatly in closely spaced coils. A form such as a plastic coffee can works great. Coil the feedline around that and tape it in place. It'll usually work as well as ferrite cores for receive-only antennas.

However those tricks also seem to attenuate the wanted signal on some bands. And household RFI tends to be worse on some bands and almost non-existent on others. In my apartment I find it necessary to reduce RFI as much as possible from around 6600-7000, but it's practically nil around 75-80m, 20m and other bands. So if I use the ferrite cores or coil trick, I might do better to remove those if I'm primarily listening to frequencies outside the funny bands.
Title: Re: MLA-30 Loop antenna
Post by: ~SIGINT~ on November 17, 2022, 0224 UTC: Quote
if your feedline is long enough, just wrap it neatly in closely spaced coils

Old "ham" wives tail. Not recommended, highly inconsistent with unpredictable results. This topic is covered in the ARRL Antenna Book. Don't waste your time and use quality ferrites from a reputable source, and just not any ferrite.

MIX 31 -> 1 MHz - 300 MHz (good for HF)
MIX 75/J -> 150 KHz - 10 MHz

https://palomar-engineers.com/ferrite-products/ferrite-cores/ferrite-mix-selection (https://palomar-engineers.com/ferrite-products/ferrite-cores/ferrite-mix-selection)
Title: Re: MLA-30 Loop antenna
Post by: Zoidberg on November 17, 2022, 0236 UTC: Quote from: ~SIGINT~ on November 17, 2022, 0224 UTC
Quote
if your feedline is long enough, just wrap it neatly in closely spaced coils

Old "ham" wives tail. Not recommended, highly inconsistent with unpredictable results. This topic is covered in the ARRL Antenna Book. Don't waste your time and use quality ferrites from a reputable source, and just not any ferrite.

MIX 31 -> 1 MHz - 300 MHz (good for HF)
MIX 75/J -> 150 KHz - 10 MHz

https://palomar-engineers.com/ferrite-products/ferrite-cores/ferrite-mix-selection (https://palomar-engineers.com/ferrite-products/ferrite-cores/ferrite-mix-selection)

I'm not a ham, old or otherwise. I don't transmit, and have never tried the coiled feedline trick suggested by some hams for transmitting.

I'm referring strictly to coiling up feedline to reduce noise in receive-only antennas. It works because... I've used it. It works as well as ferrite cores. I've compared both side by side many times.

Same pros and cons apply to both methods. Ferrite cores and coiled feedline can reduce noise without attenuating signal on some bands, not so well on others. In many experiments I find they work identically.

But ferrite chokes are indispensable for reducing noise on audio patch cables (for off air recordings, etc), USB cables, and some power cords. It's always a trial and error thing. Many shielded cables come with small ferrite chokes on one or both ends, but they tend not to work well unless the cable is looped at least once through the choke. Ferrite chokes usually work best with two or three loops, so I buy them oversize.

Coiling shielded audio patch cables *can* work, but ferrite chokes are easier -- you don't need excessively long cables in order to have enough material to coil up.

Coiling unshielded cords does nothing, so it won't help to coil up power cords from a noisy converter. Better to just get a better quality power adapter. The one that came with my Palstar spews RFI, but I replaced it long ago with some very good, quiet power adapters from Radio Shack -- no longer available, alas.
Title: Re: MLA-30 Loop antenna
Post by: RobRich on November 17, 2022, 0713 UTC: You ideally want substantial resistive choking across the desired frequency range(s). That typically means ferrites if being deployed for a wide swath of frequencies, like across multiple HF bands.

http://www.karinya.net/g3txq/chokes/

Your can obtain moderate resistivity with an air-core choke, but it is generally limited to a single HF band or so. The downside for muti-band usage is it can present a largely reactive profile on other bands, which can actually make common-mode worse.

The reality is if an air-core feedline choke seems to work across the whold HF spectrum, the antenna and feedline system probably does not present significant common-mode and/or much RFI/EMI ingress anyway.
Title: Re: MLA-30 Loop antenna
Post by: TRI International on November 17, 2022, 2218 UTC: I have one up / not impressed it amplifies just about everything it hears good or bad my long wire seems to do much better so I go with that.
Title: Re: MLA-30 Loop antenna
Post by: ChrisSmolinski on November 18, 2022, 1206 UTC: Quote from: TRI International on November 17, 2022, 2218 UTC
I have one up / not impressed it amplifies just about everything it hears good or bad my long wire seems to do much better so I go with that.

[Relatively] small loop antennas can work well, my 2m x 2m crossed parallel loop for example. OK, that's a bit larger than an MLA-30, but you get the idea, still relatively small vs a passive HF antenna. And others have made smaller loops using a quality pre-amp, like the LZ1AQ designed I used.

But that's (one of) the key factors - you need a decent pre-amp. I've lost track of the loops discussed in this thread as well as the "best MWDX antenna" thread, but I recall one loop used a video amp IC as the pre-amp, with the expected dismal results.

The other is you absolutely need to get the loop antenna outside if possible. If it was still 1975 when the only real sources of indoor RFI were dimmer switches and a TV, sure you could use it inside. But today the average home is a cesspool of RFI/QRM generators. Once the antenna picks up RFI, no amount of ferrite cores will fix that. A simple random wire antenna outside will quite likely outperform a loop antenna in the shack. Perhaps by a wide margin.

Yet another factor is that many receivers, especially portables, easily suffer from overloading. This results in images and all sorts of other problems. A stronger s meter signal does not mean the active antenna is going to perform better. In addition to overloading, you have possible problems due to the (low cost) pre-amp itself. Any amplifier adds noise, some more than others.
Title: Re: MLA-30 Loop antenna
Post by: JustGreg on November 18, 2022, 2356 UTC: I have a MLA-30. It works, but, a bit noisy. I did check and the MLA-30 uses a video amp IC which is neither matched or has a good noise figure. It does work well to listen to shortwave broadcasters. It is not the best for free radio stations or weak signal stations. For its price, it is not bad. It does beat a the whip antenna on a portable radio for shortwave.
Title: Re: MLA-30 Loop antenna
Post by: RobRich on November 20, 2022, 0547 UTC: On the potential local noise issues with the MLA-30 is the power supply being used. Many USB wall warts are quite noisy. True OEM Apple chargers tend to be the quietest consumer models I have tried. Otherwise a battery power bank might be a better option if intending to use the USB port.

A basic bias tee is easy to build or cheap enough to buy, and I recommend either a 9v-12v linear regulated power supply or battery power source.

The included bias tee can be modified as well. You can bypass the voltage converter by tracing the circuit back from the USB port, then breakout your new power feed to an external source. I popped out the now-unneeded USB port to run the new power supply wiring.

I have yet to actually use my original MLA-30 much, but what little testing I did was using a 9v battery.

Also I received a MLA-30+ awhile back. I might do some experimenting with it in the near future.
Title: Re: MLA-30 Loop antenna
Post by: Ray Lalleu on January 04, 2023, 1355 UTC: to Kenotic :
you got lots of good advices, I just can add one :
begin by weeding out the pesty devices in your own home,
for those you can't remove, add an EMI/RFI filtered power cord extension,
don't mind about the dB announced (the differences are about the way they are measured and announced), just put them drawn so that the noise can't easily jump from one side to the other.
Beware, some devices are making more noise when set waiting 'off' than when being on, and also some have kind of energy stocking so the on-off switching has no immediate effect.

Of course, if you have any kind of networking through the power lines, throw it in a hurry to the dump !
Title: Re: MLA-30 Loop antenna
Post by: ~SIGINT~ on January 04, 2023, 1442 UTC: Quote
today the average home is a cesspool of RFI/QRM generators

I concur with that comment. I have been hunting down a strange pulsing / data RFI since I moved in to this home 6 months ago and stumbled across it by accident yesterday. Unexpectedly, it is the HVAC control module and user console chatting away. This was completely unexpected but a google search revealed that this is not uncommon. Now I have to figure out how to filter this bad boy.

One of the easiest ways to find some of this RFI/EMI is by using an Inductive Amplifier such as the one found in the 200EP Inductive Amplifier Line Finder Cable Tester Portable Tone Generator Kit. The kits or the inductive amplifier are abundant on Amazon and eBay and are relatively inexpensive. This is how I stumbled upon the noisy HVAC system yesterday by locating and tracing abandoned cables in the basement ceiling.

Here is what a kit looks like (and the industry acronym for it is a "fox and hound":
Progressive 200EP Inductive Amplifier 77HP (https://www.aaatesters.com/progressive-200ep-inductive-amplifier-model-200-ep-progressive-200.html)
Title: Re: MLA-30 Loop antenna
Post by: Ray Lalleu on January 04, 2023, 1521 UTC: Quote from: ~SIGINT~ on January 04, 2023, 1442 UTC
Quote
today the average home is a cesspool of RFI/QRM generators

I concur with that comment. I have been hunting down a strange pulsing / data RFI since I moved in to this home 6 months ago and stumbled across it by accident yesterday. Unexpectedly, it is the HVAC control module and user console chatting away. This was completely unexpected but a google search revealed that this is not uncommon. Now I have to figure out how to filter this bad boy.

One of the easiest ways to find some of this RFI/EMI is by using an Inductive Amplifier such as the one found in the 200EP Inductive Amplifier Line Finder Cable Tester Portable Tone Generator Kit. The kits or the inductive amplifier are abundant on Amazon and eBay and are relatively inexpensive. This is how I stumbled upon the noisy HVAC system yesterday by locating and tracing abandoned cables in the basement ceiling.

Here is what a kit looks like (and the industry acronym for it is a "fox and hound":
Progressive 200EP Inductive Amplifier 77HP (https://www.aaatesters.com/progressive-200ep-inductive-amplifier-model-200-ep-progressive-200.html)

That site does not specify to what frequencies that tester is sensible.

I'm just using an old small Sony radio !
Title: Re: MLA-30 Loop antenna
Post by: ~SIGINT~ on January 04, 2023, 1616 UTC: Quote
That site does not specify to what frequencies that tester is sensible.

It is only as good as the speaker that is in the unit and your hearing --- audio frequency range. The key is if it is leaking out of the cable or device, it is leaking into the antenna. I also use my HP/Agilent spectrum analyzer or ICOM IC-705 with a magnetic sensing loop but not everyone can afford that. You can easily find dirty wall warts, LED / fluorescent lights etc ... with the inductive amplifier probe. A used one will only set you back about $20.00. Have to start somewhere.
Title: Re: MLA-30 Loop antenna
Post by: RobRich on January 04, 2023, 2145 UTC: The tinySA is neat gadget for those wanting a basic SA but not needing a lab-grade spectrum analyzer.

https://www.tinysa.org/wiki/
https://tinysa.org/wiki/pmwiki.php?n=Main.Buying

I have the original model, though there are now models with larger screens, higher frequencies, and whatever other options.... for more money, of course. ;)
Title: Re: MLA-30 Loop antenna
Post by: Teotwaki on January 10, 2023, 1916 UTC: I bought a Chinese MLA-30+ and modified it a little. I desoldered most of the DC-DC converter in the bias T and ran in a line from a 12.6vdc linear supply. I tossed the thin stainless steel loop wire too. I took some aluminum jacketed 1/2" coax and made a loop. I squashed the jacket flat on each end, bent a 90 degree tab and drilled it. It seems to be about 2.9 uH

The antenna's output is run through a Navy surplus multicoupler that has a great 2 - 32 MHz preselector filter before the amplifiers.

Despite all of the MLA's engineering flaws in the amplifier design it performs fine mounted up high, outdoors when compared to an untuned 70' end fed wire. That leads me to believe a correctly designed active loop could perform even better.

(https://i.ibb.co/RzzrLKx/image0-12.jpg)

The DW beacon
(https://i.ibb.co/gDKkLg5/image1-2.jpg)
Title: Re: MLA-30 Loop antenna
Post by: Pigmeat on January 13, 2023, 0253 UTC: I've built a number of passive loops over the years, starting w/ a MW loop from a schematic from Radio Nederlands. I screwed that one up royally, but it worked on 90 and 40/41 meters with the Walkman tuning cap I used with it. I was able to dx Papua New Guinea, something I wasn't able to do with my wire antenna's and get rough headings on my fellow pirates and found most of them were full of crap about where they were tx'ing from. So was I, so there were no hard feelings, just laughs.

Passive loops of that size, one meter, on HF work about as well as a 60 ft. outdoor wire, but they're directional and null interfering stations to an extent, so there's plenty to listen to. You can simply set them by the window and have fun. I used to put them on a picnic table in the backyard in warm weather, but the neighbors always asked a lot of questions. (I used nylon bags full of gravel to tighten the wires on my dipoles. They thought I was practicing Voodoo, and the bags were to keep bad luck away. Lol.)

I've never tried the MLA-30, but I have listened to online SDR's using it. They seem to work well and are quiet, but I don't know if the owners have modified them? Most radio heads like to tweak their antenna's, and I suspect many of MLA-30's I've encountered have been tweaked. I know for a fact one of them has, as the owner is an old friend. It was sounding good earlier tonight. Have fun playing with them.
Title: Re: MLA-30 Loop antenna
Post by: RobRich on January 14, 2023, 2238 UTC: From one of my posts in the MW thread....

Quote from: RobRich
Lowered voltage at the bias tee I was using to feed the MLA-30 preamp down to 4.5v last night. Add some voltage drop due to 75' of RG-6 feedline. Gain barely dropped at lower-HF bands and MW, while SNR likely improved. I still need to check voltage versus gain on upper-HF bands.

Positive supply voltage for the TL592B differential amp is listed at 3v to 8v. That tracks with my results. Gain at 3v (minus line loss) dropped considerably. The preamp at 1.5v dropped out.

12vDC as supplied by the stock USB->12vDC boost regulator in the bundled bias tee is likely overdriving the amp IC and potentially affecting SNR. YMMV, of course.

Dropping voltage might improve SNR with the inexpensive video preamp IC used in the MLA-30 design. I assume the MLA-30+ uses the same or similar chip.
Title: Re: MLA-30 Loop antenna
Post by: alpard on January 17, 2023, 1410 UTC: I sold all my radio stuff to buy electric guitars and amp, and have been away from radio hobby for couple of years. I am recently back to the radio.
From my memory MLA-30+ was OK, but for serious DX stuff, it lacked a bit. On LW it was non working but from MW to SW, it was OK.
DXing for the low power AM stations at nights, the Wellbrook ML was far better. But Wellbrook was about 10 times more expensive.
Title: Re: MLA-30 Loop antenna
Post by: Teotwaki on January 18, 2023, 1712 UTC: Quote from: RobRich on January 14, 2023, 2238 UTC
From one of my posts in the MW thread....

Quote from: RobRich
Lowered voltage at the bias tee I was using to feed the MLA-30 preamp down to 4.5v last night. Add some voltage drop due to 75' of RG-6 feedline. Gain barely dropped at lower-HF bands and MW, while SNR likely improved. I still need to check voltage versus gain on upper-HF bands.

Positive supply voltage for the TL592B differential amp is listed at 3v to 8v. That tracks with my results. Gain at 3v (minus line loss) dropped considerably. The preamp at 1.5v dropped out.

12vDC as supplied by the stock USB->12vDC boost regulator in the bundled bias tee is likely overdriving the amp IC and potentially affecting SNR. YMMV, of course.

Dropping voltage might improve SNR with the inexpensive video preamp IC used in the MLA-30 design. I assume the MLA-30+ uses the same or similar chip.

Rob

Thanks for bringing up the suggestion for the lower supply voltage.
(https://mediaprocessor.websimages.com/width/920/crop/0,0,920x347/www.g8jnj.net/MLA30%20Circuit%20Outline.png)
The reverse engineered schematics do not show any on board voltage regulator so I agree that a +12v supply is too high, assuming the Chinese used a chip specified the same as the TL592B. I've dropped the voltage into the bias Tee to +6vdc and the loop's amplifier gain seems the same. I'll try to make some signal strength measurements later this week.

Jim
Title: Re: MLA-30 Loop antenna
Post by: Teotwaki on January 18, 2023, 1740 UTC: Here is a schematic of the AL1530 Wellbrook loop
(https://www.george-smart.co.uk/wordpress/wp-content/uploads/2017/01/WGL_Schematic.png)

The writeup is very interesting too.
https://www.george-smart.co.uk/projects/wellgood-loop/wellgood-loop-history/