MLA-30 active loop antenna

[vinlove]

Not sure how this youtuber  claims that MLA30 is better RX performer than 10times more expensive active loop then.     

[vinlove]

Please listen and watch  the review closely to the end. He says he doesn't understand why you have paid 10 times more money to the active loop antenna that doesn't perform any better than MLA30? He is not saying this by random emotional response, but his review is based on the tests that he had gone through side by side careful comparisons on the loops on the real SWL performance.

[A.Z.]

Please listen and watch  the review

I can listen and watch, but sincerely I prefer judging the antenna from what I see/hear here; as I wrote I do have an MLA-30+ here and, the unmodified, original antenna is very noisy and absolutely NOT comparable with higher priced ones, I wrote it and I'll repeat it; this doesn't mean that the MLA-30 is "crap", there's room for improvement, but saying that, as it comes, it's better than (say) a WellBrook is simply untrue, then if you don't want to hear this, up to you, I try to be objective

[vinlove]

I have never had Wellbrook, so just trying to figure out, how good it is by the reviews and the owners' comments on it

I wonder if it can hear the low powered am stations with 1kW - 10kW on the Tropical bands coming out from South America every night? = Peru, Brazil and the other countries in the region.   Or RNZI on 9700 kHz and 11725 kHz around mid day? These are tough DX signals to copy well in Europe.
My MLA30 can hear them only occasionally when the band condition is excellent. I can hear the Cuban station R. Rebelde and Habana on 5 Mhz every night very strong with MLA30.
Have you tried listening to them with your Wellbrook and MLA30?   Are you in Italy? Your ID has the Italian flag.

[A.Z.]

I have never had Wellbrook, so just trying to figure out, how good it is by the reviews and the owners' comments on it

Nor I did, but time ago a friend lend me one for some time, and it's a good antenna, it has some hardware design flaws, but other than that, it works very well, the preamp was designed to reduce both noise and intermodulation to very low levels; comparing the MLA-30 to a WellBrook (or other high level loops) isn't fair, it's like comparing a cheap car with (say) a Maybach

I wonder if it can hear the low powered am stations with 1kW - 10kW on the Tropical bands coming out from South America every night? = Peru, Brazil and the other countries in the region.   Or RNZI on 9700 kHz and 11725 kHz around mid day? These are tough DX signals to copy well in Europe.

I think so

My MLA30 can hear them only occasionally when the band condition is excellent. I can hear the Cuban station R. Rebelde and Habana on 5 Mhz every night very strong with MLA30.

Yes, I can pick those up too, depending on propagation conditions, with my LLD; didn't yet put up the MLA-30 due to some real life issues, but I'm planning to do so next January; yet, from the tests I performed inside, the noise level from the MLA-30 (using its bias-tee) is very high, it may be fixed, but "as is" the antenna isn't exactly a good one

Are you in Italy? Your ID has the Italian flag.

Yes

[vinlove]

What receivers do you own and use? Which ones are the best?

[A.Z.]

What receivers do you own and use? Which ones are the best?

what's this ? A police drill ?

[vinlove]

Just for interest ...
What has police got to do with shortwave radio receivers? 

[charliedelta]

Yeah subjective A/b measurements with  20 db of fading is hardly science.

The proper way to do it is first to establish the noise floor of the  2  preamps with the equivalent inductance as a load.

Then maybe  using a small fixed radiating loop connected to a signal generator to generate  a  small nominal fixed field strength and then measure the signal to noise ratio.

In all cases a tuned  loop will blow all these amplified loops out of the water in terms of signal to noise ratio because simply thats the laws of physics not brand name or loop amplifier design. Its one of the reasons that professional EMC loops cant even detect or measure the  kinds of interferences experienced by hams.

 Simply put the amplifiers noise floor covers the  interfering signals.Even EMC professionals seem to  fail  at understanding something as basic  as the noise floor performance of their antennas.  The EMC industry especially when it come measuring true interference levels on the HF bands are not using suitable equipment. They have  very expensive calibrated loop antennas  and expertise but have difficulty understanding that their equipment is covering up the signals that they supposed to be measuring.

Shortwave listeners make the same mistake when trying to compare noisy amplified loop antennas. Its best to measure the signal to noise ratio under controlled conditions.  When you do this you will be shocked how poorly most of the "magic magnetic" loop antennas work.

It is interesting that he thinks that MLA30 is quieter than W6LVP which costs 10 times more expensive.
He is an experienced SWL / BCL and knows what he is talking about, I thought.

Lots of talk, no proof; again, having the MLA-30 (plus) in my hands and having other antennas (and having tried more in a past), the MLA-30 may be modified to become a pretty decent active loop, but even then, it won't be up to par with other loops (either built or bought); this does NOT mean that one should throw the MLA-30, just that the latter needs (and really needs) some modifications.

[vinlove]

MLA30 is still a great antenna for general listening HF and MW.  For digging out serious DXing coming from remotest places transmitted with low power, yes one needs quieter antennas. Passive antennas are quieter, but also not sensitive enough?  Therefore we are after the active loops with quieter reception?  I would love to compare MLA30, Wellbrooks and passive loops for the DX signals RXing side by side.  It will be obvious. Good antennas will hear with intelligibility, poor antennas will not.

[A.Z.]

MLA30 is still a great antenna for general listening HF and MW.  For digging out serious DXing coming from remotest places transmitted with low power, yes one needs quieter antennas. Passive antennas are quieter, but also not sensitive enough?  Therefore we are after the active loops with quieter reception?  I would love to compare MLA30, Wellbrooks and passive loops for the DX signals RXing side by side.  It will be obvious. Good antennas will hear with intelligibility, poor antennas will not.

the MLA-30, as it comes, may be ok for MW listening and w/o pretending too much, but willing to get more serious and/or get good performances on other bands (too) it needs some modifications, and that's the good thing, since even if the preamp circuit is potted, there are some easy and cheap mods which will greatly improve the antenna performances; the "must do" ones are the ones related to the noisy bias tee and to the poor coax which comes with the antenna, then there are the others which will further improve it, and considering the low price of such an activeloop and the fact that the mods are easy and cheap, I believe that the MLA-30 antenna may be worth its price

[vinlove]

I have tried a defunct MFJ 1024 active antenna bias-T bit with MLA30, and it worked impressive.

https://www.hamradio.co.uk/aerials-antenna-manufacturers-mfj-antennas/mfj/mfj-1024-swl-outdoor-active-antenna-50-khz-30-mhz-pd-5443.php

But my junk box found MFJ-1024 bias-t bit has a fault with the connection somewhere, it was giving intermittent problems.
After overhauling the 1024 beat-T unit, it seems it will work well with MLA30.  A future project for me.

[A.Z.]

I have tried a defunct MFJ 1024 active antenna bias-T bit with MLA30, and it worked impressive.

https://www.hamradio.co.uk/aerials-antenna-manufacturers-mfj-antennas/mfj/mfj-1024-swl-outdoor-active-antenna-50-khz-30-mhz-pd-5443.php

But my junk box found MFJ-1024 bias-t bit has a fault with the connection somewhere, it was giving intermittent problems.
After overhauling the 1024 beat-T unit, it seems it will work well with MLA30.  A future project for me.

That's what I tried to say, the original bias tee unit, due to the 5 to 12v multiplier IC generates a lot of noise, so either modding or replacing it will lower the noise floor and improve reception, the other mods I suggested will further improve that cheap antenna performances

[vinlove]

Yep, the MLA30 fed with the MFJ 1024 bias-T 12V direct, was like dead quiet, and sucking in the weak signals like a most powerful pump.  There was no band noise at all just silence, and whenever tuned to weak signals, it blasted out with highest S to N ratio. It was amazing, but unfortunately my junk box found MFJ1024 had some serious misconnection problems on the antenna connection.  I had to take it off and back to the junk box until I have some time of peace and quiet.

[A.Z.]

Yep, the MLA30 fed with the MFJ 1024 bias-T 12V direct, was like dead quiet, and sucking in the weak signals like a most powerful pump.  There was no band noise at all just silence, and whenever tuned to weak signals, it blasted out with highest S to N ratio. It was amazing, but unfortunately my junk box found MFJ1024 had some serious misconnection problems on the antenna connection.  I had to take it off and back to the junk box until I have some time of peace and quiet.

well, you may either mod the original bias tee box, excluding the multiplier IC or repair the MFJ box you found, it shouldn't be difficult

[edit]

as for modifying the original bias tee, check the circuit which I already posted and look at this pic

https://pbs.twimg.com/media/EKpngVgWoAE4OTl.jpg

as you can see, the bias tee isn't potted, so cutting off the voltage multiplier IC to exclude it, and soldering two wires (+/-) to the USB socket won't be difficult, such a mod would left in place the builtin filters and the attenuator, while allowing to power the antenna using a "clean" 12V DC supply

[vinlove]

Modding would be an interesting project for MLA30.  But it is good as original is too.
It receives weak DX signals the other antennas cannot hear many times.

[Co6aka]

Assuming the schematic I found and posted in #21 is correct...and that the OpAmp is a AD8129...and that I'm not still smashed from too many holiday cheers...

The whole "GNDD" thing is a problem. The input "filter" components should all be fully differential, connected between the two inputs, and should be isolated from C9, C10, C15 and the rest of the "PCB Ground" thing.  But the input "filter" and impedance matching to the OpAmp input is all wrong anyway. Assuming the OpAmp is a AD8129, model the circuit in your favorite simulator. Try input matching with a transformer and getting rid of the resistors, and use a center-tapped primary so the loop will be DC-referenced. The transformer's frequency response characteristics can be leveraged to act as part of the filter, with the rest of the filter components being between the transformer and the OpAmp.  Power with a clean 10-12V source.

Basically, it's a balance of compromises that works out to the "best" overall frequency response and noise figure you can derive with the components. Signal to noise ratio is the most important, so you must consider factors such as atmospheric noise plus antenna factor versus frequency -- don't get lost trying to perfectly match impedances; it's along the lines of matching for lowest noise figure in UHF/SHF GaAsFET preamps.

The loop element itself should be low inductance. That wire element is handy for portability, but as a permanently mounted antenna it should be replaced. Measure your loop's inductance with a LCR meter, or calculate it, or do both, and then for testing purposes replace it with a inductor. The amplifier can then be tested by placing it in a metal or screened box.

Probably significant improvements can be obtained, but the overall RF performance is hard-limited by the OpAmp.  My experiments have all been with discrete components, which far exceed the capabilities of the AD8129, but I wonder what can be achieved with modern high-end ADC input buffers.

[A.Z.]

Assuming the schematic I found and posted in #21 is correct...and that the OpAmp is a AD8129...and that I'm not still smashed from too many holiday cheers...

The schematics can be found on Martin's website, here (also linked in starting post)

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

and, according to the informations found there and on other sites, the IC should be a TL592B

the input "filter" and impedance matching to the OpAmp input is all wrong anyway.

exactly so, and the preamp circuit is fully potted (the bias-t is clean), so willing to avoid un-potting it, the only workaround I envision is adding an impedance transformer between the loop and the PCB input to, at least, offer high impedance on both sides of the lowpass

use a center-tapped primary so the loop will be DC-referenced.

How would you connect the tapped transformer ?

Power with a clean 10-12V source.

and that's where the un-potted bias-tee circuit comes to play, excluding the voltage multiplier IC and powering the bias-tee using a clean 12V source eliminates the noise generated by the bias-tee unit and improves quite a lot the overall performances of that cheap loop

Basically, it's a balance of compromises that works out to the "best" overall frequency response and noise figure

right, don't expect to turn the MLA-30 into a $$$ loop, but with some simple mods it can be improved a lot and become a good "cheap loop" offering more than decent performances and helping people living in RF noisy places

The loop element itself should be low inductance. That wire element is handy for portability, but as a permanently mounted antenna it should be replaced.

Didn't (yet) replace the loop, but the idea is to use a piece of copper pipe to replace the thin loop (and probably make it a bit larger than the original), I've also considered the idea of putting together a so called "hermes loop" (two loops in parallel connected at bottom), but I think I'll start simple; all I can say is that, while the MLA-30 antenna "as is" (as it comes) has a number of defects and a too high noise floor, with some simple and cheap modifications can be turned into a good performing antenna and, considering its price, I believe it may be worth buying also since it can easily be used as a "carry around" antenna

[vinlove]

Still using the stock MLA30.  I have a longwire, dipole and MLA30 all connected into an antenna switch.
Many times, MLA30 can copy the weak signals that other antennas cannot copy at all.

I replaced the MLA30 element to thicker Earth wire, but now gone back to the original thin wire, because it looks less obtrusive in the room.
The performance was the same, cannot detect any difference between the thin original wire element and the thick earth wire element.

I will replace the bias-tee with either MFJ 1024 junk box found unit when repaired, and some other active antenna bias-tee to compare with the MLA30 bias-t.

But just to copy normal DX signals, the stock MLA30 can do the job OK in most cases.

See some of the videos on youtube side by side comparison between MLA30 and more expensive active loops such as Wellbrook and W5LVP, and I recall that there were not that much clear difference between them to be honest. I will try to watch them again. 

The most important factor in DXing seem the time of day and the band condition. When the path opens up and the condition is right, you can copy the rarest DX signal with even built-in whip antenna. And even for the same signal, sometimes wire can copy when other antennas cannot, and vice versa.  But in general, I find MLA30 better antenna than others even as the stock original version.

[A.Z.]

I believe you may need to get in peace with yourself, you start saying that with a given mod (like bias tee) the antenna works better, just to come back saying that the stock one is ok; if you think that the stock MLA-30 is ok for you, then that's fine with me, get what you like, but sincerely, in my opinon (and not just mine) the "plain" version of that active loop has a number of problems.

[vinlove]

My comment on the MFJ 1024 Bias-T with the MLA30 was not some testing results.  But it was a quick trying out, and even that was obstructed by the faulty 1024 Bias-T unit.
I don't think that you can get some concret results or answers on Radios and Antennas performance just like that.
If you reflect about your RXing and DXing times, you know how complicated the whole thing is.  It is affected by many factors = the band condition, propagation, time of the day, RFI level in your QTH, your radio capability and setup, and your RX antenna capability and set up.

Just revisiting on these points

[A.Z.]

My comment on the MFJ 1024 Bias-T with the MLA30 was not some testing results.  But it was a quick trying out, and even that was obstructed by the faulty 1024 Bias-T unit.
I don't think that you can get some concret results or answers on Radios and Antennas performance just like that.
If you reflect about your RXing and DXing times, you know how complicated the whole thing is.  It is affected by many factors = the band condition, propagation, time of the day, RFI level in your QTH, your radio capability and setup, and your RX antenna capability and set up.

The stock MLA-30 antenna has a noise floor level from 10 to 20 dB higher than other antennas, I've seen on the spectrum display it by comparing it with other antennas and it has been confirmed by others, so it's not a matter of propagation/location/conditions/whatnot but a matter of fact.

[vinlove]

It still receives the DX signals the other antennas cannot hear.
So it is the antenna being used most times.

Don't get too blinded and tied into the graphs and figures, but listen to your radios with the
antenna, and ask yourself, can  it receive the weak DX signals you are after?

If it can, then don't change it. If it cannot, then change it, if you can, and make it hear the signals.
Otherwise, commit it to the bin.

[A.Z.]

It still receives the DX signals the other antennas cannot hear.
So it is the antenna being used most times.

I'm happy you're satisfied, in my case the MLA-30 wasn't up to par with other antennas I have, and since I'm a "hard headed" kind of guy, I decided to find a way to improve it, and I did, then, if you feel that the stock setup works for you, go for it, in my case I found it to be too noisy with respect to my other antennas and to other loops I used, so I went on doing some viable mods and the results were/are more than good, now weaker signals don't get lost in noise !

[Lord of nothing]

So what is the next cheapest Antenna in comparison who is better and affordable to?