MLA-30 active loop antenna

[A.Z.]

I decided to pick up the newer MLA-30+ to see if there was any effective improvement over the MLA-30; judging from what I've seen/read, the main change is that now the performance at higher frequencies should have been improved; anyhow, I went on placing the order on Amazon and after 4 days got the antenna delivered.

Last weekend had a bit of time in my hands, so decided to give the MLA-30+ a quick test, just to ensure it was -at least- working, so I hooked up the antenna indoors placing the preamp box on a table "lazy susan" style and using a cardboard pipe to support the (very thin) steel wire of the loop, connected the preamp to the bias-t box and the latter to the receiver, plugged a 5V DC supply to the bias-t box and ran my SDR

Propagation wasn't so good, but signals came in, yet even the "+" model has the very same issue of the previous model, that is, the bias-t is very noisy; just to give you an idea, using the LLD (Linear Loaded Dipole) I've on my balcony, the noise floor is around -120 to -130 dB, plugging the MLA-30+ the floor goes up to -90 to -100 dB which, in my book, is quite a lot of noise; to confirm that the issue was due to the bias-t unit, I picked another bias-t used for a miniwhip antenna and used that one to power the MLA-30+ with a 12V DC supply, with the latter, the noise floor on the loop went down to -110 to -120 dB which, considering that the antenna was indoor, is a decent level

So I believe that modifying the bias-t to bypass the DC-DC converter and powering it directly through a 12V DC supply is a need and not an option (alternatively one may either use another bias-t unit or build one); the modification (didn't yet go on and make it) is shown in the attached picture

to perform it I'll open the bias-t box (whose circuit is luckily unpotted) and cut the traces maked in red in the picture, so excluding the (very noisy) voltage converter from the circuit while leaving the passive filtering components in place; at that point it will just be a matter of soldering two wires to pins #1 and #5 of the (now unused) USB port and using them to power the bias-t using a decent 12VDC power supply

Whith the above modification alone (and by the way, placing the antenna outside), the MLA-30+ should become a pretty decent performer; then I'm also planning to add a BNC connector to the antenna, the process, judging from this video

should be pretty easy, although, instead of using a single snap-on choke as the folk in the video did, I'll probably cut the coax a bit longer and use it to wind a "Guanella" choke which, for sure, will work far better, the modification will also allow me to use a longer coax ... and a better one (the one coming with the antenna isn't exactly "first class")

While with the above modifications, the MLA-30 will become a decent antenna, I believe that to really improve it some further modifications will probably be needed; if you look at the MLA-30 informations found on the G8JNJ web site and check the notes and the schematics, you'll see that another issue with the MLA-30 (and I suspect with the "+" too) is the very bad design of the input lowpass filter stage; such a filter expects to (at least) see the same (ok, a similar) impedance on both its ends, but in the MLA-30 case, the filter sees low impedance on the loop side and high impedance on the preamp input one; now, Martin (G8JNJ) had an unpotted circuit so he was able to try placing some resistors between the loop input and the board ground, but in my case, unpotting the circuit could result in a damaged board, so after some head scratching I decided that I'll try a different mod, that is placing a transformer between the loop and the preamplifier input, the transformer will be something like this  with the low impedance winding going to the loop and the high impedance one going to the preamp; given the very low impedance of the loop, I believe that a 1:16 transformer should work, so my idea is to wind 2 turns to the loop and 8 turns to the preamp (turns ratio 1:4 = impedance ratio 1:16) on a small binocular core (a FairRite #73 or similar should do)

To install the transformer I'll unscrew the two side screws with the winged nuts used to support the loop, fold the two rails connecting the screws to the preamp input down toward the (potted) board and solder the high impedance side of the transformer to them, then I'll reinsert the screws (nuts, washers, windged nuts) and connect the low impedance side of the transformer to them, this way I hope to (at least) improve a bit the preamp performances... although I'll probably have to fiddle a bit with the transformer trying different ratios to find the better working one

Ok, that's the plan, at least; will probably find time to start with the project next January or February and, at least, perform the first two modifications (bias-t and bnc+choke), posted the above just in case someone else, owning an MLA-30, wants to try the same mods

[edit]

Forgot; another planned mod is to replace the very thin steel wire used for the loop with some copper pipe or aluminium strip, that would be the easiest mod and may (hopefully) further improve the antenna performances

[Co6aka]

Basically, in a loop antenna you want to minimize loop inductance and resistance*, but a properly designed loop amplifier will be designed with its attached loop inductance and resistance in mind.  Typically, you design and construct a loop element to minimize inductance and resistance, then design the amplifier for it.  Anyway, you'll likely see improvement with anything "better" than that silly wire loop.

FWIW, for receiving purposes where loop CURRENT is very low, very low loop resistance isn't as critical as it is for transmitting, so aluminum is fine for the loop element. In my experiments with transmitting loops back in the early 80s, copper flash worked slightly better than aluminum flash, but of course it was much heavier so the frame had to be strengthened. 

* You also want to maximize area, while keeping the circumference (or diameter) within dimensions appropriate for the highest frequency of use.

(Another factor to consider for a loop amplifier is noise figure, the lower the better, which means eliminating resistors attached to the input. Another is linearity, of course.)

[A.Z.]

Co6aka, you're right, but the point here is trying to improve the existing MLA-30/MLA-30+ loop; now, the preamp circuit is fully potted and un-potting it would be quite a hassle and may result in damages to the board, so I decided it won't be worth going that way, what I'm planning is a series of modifications to improve the existing circuit/antenna without too much effort and, by the way, without pretending to obtain a "wellbrook" (or the like) at end 

As for the loop material, I agree about the fact that some copper tubing would be the best choice, but then I think I'll explore other (cheaper) materials too, again the target isn't to turn the MLA-30 into a "super antenna" but to apply it some easy/cheap mods which anyone could perform and which will improve the loop performances, nothing else

[vinlove]

Is Wellbrook a lot better performance than MLA30? The price is about 10 times higher.
My MLA30 was 25 euros including delivery.

I saw a youtube video, that says MLA30 is as good as any other active loop on the market.
But I don't know how the Wellbrooks like. I have never used it.

[A.Z.]

Is Wellbrook a lot better performance than MLA30? The price is about 10 times higher.
My MLA30 was 25 euros including delivery.

Well, it's like comparing apples and oranges; the MLA-30 is a very cheap loop and has a number of design flaws, but it's cheap and the flaws can (to some extent) be corrected, the WellBrook loops are "top of range" but cost a lot more; then, willing to build a wellbrook "clone" yourself, you may find the informations and schematics here although, sincerely, if you're going for a build, I'd suggest you to consider this one

I saw a youtube video, that says MLA30 is as good as any other active loop on the market.
But I don't know how the Wellbrooks like. I have never used it.

Youtube videos aren't "the ultimate truth"

As I wrote, I have an MLA-30 here and while I didn't fully test it, I can confirm that the bias-tee unit is VERY NOISY, that may be fixed, sure, but if one is going for an MLA-30 he'll need to be prepared to modify it or, at the very least, modify (or replace) the bias-tee unit

[vinlove]

Here is the link for the review comparing MLA30 vs. W6LVP.


The reviewer thinks MLA30 is better than W6LVP which costs 10 times more.
W6LVP is not Wellbrook, but I think they cost about the same.

[vinlove]

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.

[A.Z.]

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]

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.

yup, maybe it would need side by side comparison on the same signal and receiver.
I am sure he has some videos on that testing = comparing MLA30 vs. other active loop antennas.

[A.Z.]

yup, maybe it would need side by side comparison on the same signal and receiver.
I am sure he has some videos on that testing = comparing MLA30 vs. other active loop antennas.

One, amongst a bunch of others (just a matter of searching a bit)

https://swling.com/blog/2019/09/david-reviews-and-compares-the-mla-30-magnetic-loop-antenna/

also see

[Lord of nothing]

When the Temperature allow I put my MLA-30 outside and the Cable goes truth the open door and I use the stock Bias-T. In my case the work good for my perspective. I could not see anything who produce a lot of noise. I would like try some better Bias-T. Is there someone who is recommend?
I dont have any Solder Iron or Power Supply or anything elese. So it must be fool proof.
Thanks

[A.Z.]

When the Temperature allow I put my MLA-30 outside and the Cable goes truth the open door and I use the stock Bias-T. In my case the work good for my perspective. I could not see anything who produce a lot of noise. I would like try some better Bias-T. Is there someone who is recommend?
I dont have any Solder Iron or Power Supply or anything elese. So it must be fool proof.
Thanks

Are you using it with an SDR ? And if so, which one ? I'm asking since some SDR units offer a builtin bias-tee option, in such a case you may connect the coax coming from the loop directly to the SDR SMA (keeping out of the combo the bias-tee box and the additional coax) and power the MLA-30 preamp using the SDR bias-tee voltage, that will be 5V, so lower than the original 12V, so gain will be lower, but the preamp will still work and noise floor will be lower

[edit]

also, in the spite of "better than nothing", consider adding to the MLA-30 coax some chokes, those may either be wound on a toroid using the coax or you may buy some snap-on chokes and add them to the coax, in such a second case, group the chokes together (a group will be at less 6 chokes, more is better) and use some tape to keep them tight together; those will help taming the noise picked up by the "not so good" coax which comes with the MLA-30, then you may also consider replacing the original thin wire loop with a fatter one (or even a piece of copper pipe)

[vinlove]

I am feeding the MLA30+ with a rechargeable phone battery 5V DC, instead of wall wart psu, and it is already making big improvement in noise.
Problem is that, the battery must be recharged when runs out. And when the voltage drops, the reception goes abnormal.

[A.Z.]

a battery is for sure better than a noisy power supply or phone charger, but the voltage multiplier inside the bias tee will stll be introducing noise

[Lord of nothing]

How about a bigger PSU like I use for CB Radio?
Like such: https://www.conrad.at/de/p/voltcraft-fsp-1122-labornetzgeraet-festspannung-12-v-dc-2-a-25-w-anzahl-ausgaenge-1-x-511410.html
I dont know what the internally use and how good the are but for my CB Radio it work good.

[A.Z.]

that seems to be a stabilized (non switching) unit, and may fit well, but you will need to modify the bias tee unit as I wrote

[vinlove]

Blimey, just found that my SDRPlay RSP1A has a BIA-T function built-in. It can be switched on the SDRUno software.
When connected with MLA30, the BIAS-T of RSP1A works, and it works very well.  Noise is well down, and signal is up.

I didn't know that before, because I got the RSP1A without any documentation, because it was cheap used one.
Thanks to this thread, I found it has the facility and I don't have to modify or upgrade the MLA30 noisy BIAS-T. 

If you use SDR, then check if it supports BIAS-T function built in. If it does, then you save time and money and effort for modding noisy BIAS-T of MLA30.

[A.Z.]

five volts

[vinlove]

yup. but seems work.
When BIAS-T is switched off from SDRUno, there is no reception.
When switched on, MLA30 is operational with good signals.

[A.Z.]

it works, sure, but gain is lower and IMD worse

[vinlove]

Did side by side testing ,and there is no noticeable difference on HF, but on MW, there is, yes.
So, if you are MW DXer, the 5V bias-t is no use for MLA30.
But if you just listen to HF only, 5V seems OK.  It is definitely quieter and same signal strength on HF.

[Co6aka]

FWIW, I use a Wellbrook ALA1530LN as a benchmark reference for my own designs -- gotta know if mine are at least up to par!

"Inside the MLA-30 Active Loop Antenna"
https://www.m0lmk.co.uk/2019/09/12/inside-the-mla-30-active-loop-antenna/

1. The MLA's DC injector contains a DC/DC converter so bypassing it and using a QUIET power source would be a good first step. Also, there's a lot of room for improvement in these injectors, in terms of power filtering, coupling DC to the antenna feedline, and receiver protection.

2. The MLA's loop amp appears to use a differential OpAmp...



...so it's certainly limited in its ability to handle strong signals (2nd and 3rd order intercept) and its noise figure (at least 3dB due to R1 and R2.) What's the Vcc for the OpAmp? Use a higher Vcc if possible.

Noise figure and 2nd order intercept are the two primary factors for your loop amplifier, and low inductance is the primary electrical factor for your loop element (also because you don't want any resonances in your loop element.) SM5BSZ has done a lot of research into low noise amplifiers for the HF range, so consult his website for ideas in this area.

3. Conducted noise on the feedline (noise from your shack to your antenna, conducted by the coax braid) is often a nasty problem, so adding two feedline chokes, one just outside your shack and one just below your antenna, is usually a good thing. I made mine with twelve jumbo 31-mix beads, arranged in a square with three on a side, sealed in a plastic utility box, with connectors on opposite sides. My loops are roof-mounted because ground level noise around here is much worse. If your antenna and coax run is ground level, it could be more effective to use metal enclosures grounded to their own rods (and then you can add lightning protection as well.)  Probably a buried coax run would be good too.

[A.Z.]

co6aka; I think I covered all your points in my initial post, the bias tee unit needs to be either modified to exclude the noisy voltage converter or totally replaced, as for the preamp, the lowpass filter at its input has a very bad input/output impedance mismatch, and as for IMD, it isn't a big issue as long as you adjust the gain trimmer for minimal gain (just the bit needed to compensate losses), then replacing the coax, adding a good choke and replacing the thin loop with a better one should further improve that cheap antenna performances, no miracles, by the way

[edit]

forgot, while "maxwell" type chokes are ok, they require quite a lot of ferrites, I prefer "guanella" chokes wound in toroids using coax, those in my experience offer better results

[vinlove]

coupling DC to the antenna feedline, and receiver protection.

Two questions.

1. Receiver protection from what? Do you mean possible damage from over voltage or current to the antenna input from MLA30? Or would it be protection from thunder and storm damage? Or  Harmful RFI damage possibilties?

2. Can Wellbrooks hear weak DX signals, MLA30 cannot hear? Any examples, if yes?

[A.Z.]

1. static and nearby tx

2. yes

it's a matter of horses for courses

[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?

[A.Z.]

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

Better than what ? If you're referring to the stock MLA-30, with its noisy bias-t unit and the other issues, then even a passive loop may beat it, but as usual, there's no "absolute best antenna", otherwise everyone would just be using that and nothing else; then maybe I misunderstood your question.

[Lord of nothing]

Well I mean a better constructed one who give even similar performance by lower noise and so on.

[A.Z.]

Well I mean a better constructed one who give even similar performance by lower noise and so on.

I see... well, in such a case, call me crazy but I still prefer "self built" ones  as for loops the Wenzel "loopifier" (which I built in several samples - for friends too) is a pretty good one, it uses the same TL592 IC, but being tuned and using a decent bias-tee design, it overcomes IMD and noise issues and gives very good results, then there are the loops from Matt (KK5JY), even if they are passive, they offer incredible performances, the "SRL" is the easiest to put together, and the "LoG" offers incredible performances on the low bands (40 meters and down), then there are a bunch other antennas I tried, but in general, when it comes to antennas and in particular RX ones, ensure to care the whole system, this means using decent coax (given you won't be using openwire) and good choking and grounding; in the MLA-30 case, this doesn't suffice since, as I already wrote, the antenna design falls short on a number of aspects, luckily those are easy/cheap to fix

[vinlove]

In this side by side test, MLA30 and the Wellbrook, the stock MLA30 was quieter?

[A.Z.]

And that should be a comparison ? Again, if you are satisfied, go for it. I'm not, so I believe it needs to be modified, please avoid trying to convince me that the stock (as it comes) MLA-30 works well, it doesn't, and I write this from direct experience and comparison ( and then it's easy to see why, looking at the bias and preamp circuits), again, if you are satisfied with the stock one, go for it, but don't try convincing me, thank you

[Lord of nothing]

For me the stock MLA-30 working better than a plain copper Wire. I would say for beginner who want see if the could receive anything (maybe because a damn neighbour in an Appartmentcomplex use Powerline).
@A.Z. for someone who have Tools and maybe a Basement, Shack,... or what ever its easy to build. Sadly I have just my Home Office with a lot of Server inside who I want to avoid anything who could produce dust or a dangerous atmospheric.

[A.Z.]

you wrote about other antennas and now they're just "copper wire" ? Are you playing some kind of joke or what ? As it is the MLA could be easily beaten by a simple wire loop or linear loaded dipole ... correcly installed ... oh well, maybe I'm just an old fart fighting windmills ... deep sigh

[vinlove]

And that should be a comparison ? Again, if you are satisfied, go for it. I'm not, so I believe it needs to be modified, please avoid trying to convince me that the stock (as it comes) MLA-30 works well, it doesn't, and I write this from direct experience and comparison ( and then it's easy to see why, looking at the bias and preamp circuits), again, if you are satisfied with the stock one, go for it, but don't try convincing me, thank you

No no, I am not trying to convince you about anything. Why should I?
I am just saying that HF and MW RXing is not that simple topic.
You just think that noise floor is low on a antenna, and blindly believe that it works best for you, but
I am trying to say that there are the other factors involved in this game.

The point of your having a antenna is that, so you could hear the signals not trying to get low noise device, so that
you could meditate or fall into trance or something.

You know that a dummy load is quiet? Yes, super quiet and will give you low SWR 1:1, but
it cannot hear the signal you are wanting to hear.

MLA30 might be a bit noisy, but it pulls the DX signals from the air and you could hear it on your radio?
And you must choose to go for MLA30, not a dummy load. That is just my point.

Whether it is a stock or not, it doesn't matter. The matter is, can it hear the signals from South America
and the Far East and South Pacific running about 10 kW or lower? Well if you can, it is a good antenna for you.
If not, sorry mate, your antenna is poor be it modded or not, be it expensive or not.

[Lord of nothing]

Well I am a beginner so its not that bad for me.

[vinlove]

Show me your logbook or list of DX signals you heard on your radios, and I will tell you how good your antenna is.

[A.Z.]

Show me your logbook or list of DX signals you heard on your radios, and I will tell you how good your antenna is.

Not sure you were asking me, anyhow, I tested the MLA-30+ after the bias-tee and preamp modifications, to do so I ran a test using the FT8 digimode for about 8 hours, and the received spots were uploaded to https://pskreporter.info which then generated the following map



not special but not bad, either; consider that before the mods, running a similar test, the MLA-30+ picked up much less stations (about 1/2); that said, even with the mods, the MLA-30+ works decently well from 7 MHz down, while going up in frequency its performances degrade very quickly; not a "super antenna" (my short LLD beats it hands down all the time), but if one has limited space I believe that, once modified, the MLA-30+ may be a good choice

[edit]

As a note, I didn't (yet) add the transformer between the loop and the preamp, and the antenna doesn't show noticeable nulls, I suspect it's due to the input mismatch, so adding the transformer may probably improve the nulling ability which, as is, is almost non existent, also, lowering the gain trimmer inside the preamp helps quite a bit reducing IMD and lowering the noise floor which in turn allows to have better reception (even of weak signals)

[A.Z.]

The point of your having a antenna is that, so you could hear the signals not trying to get low noise device

I think you're missing an important point; if the noise floor, due to a bad preamp or feedline is high, weaker signals will get lost in noise, so you will loose them, that's why it's a good idea trying to reduce the antenna system (by system I mean the whole setup, from the rig to the antenna, including feedline and grounding) noise, by the way, you can't reduce atmospheric noise, but for sure you can reduce common mode noise, place the antenna as "free" and far away from the local "noise cloud" (or "elettrosmog" if you prefer) as possible and minimize the noise introduced by whatever preamp, and this will improve reception, especially if you're hunting weak signals

[vinlove]

Sorry but FT8 is not interest of me. Never have used or tried that mode.
So, I cannot tell you how effective your modded MLA30+ is with the DX map.

If it were BCL DXing list, certainly it is impressive. But FT8? Is it not some digi mod?
For digi mod, I would prefer using Skype or some phone chat apps, and they connect the whole
world without any external antenna on the phones.

I am only interested in the traditional mode which are AM, SSB and CW and maybe FM in BCL.
Because this BCL SWL activity is a traditional communication activity.

Anyhow, on the noise floor issue, I am not sure if quieter antennas are better. I would say yes and no.
Sometimes it is good, if they can receive the weak signals you want to listen to, but some antennas
are just queit and deaf, and they cannot hear the signals either.
So, I wouldn't say the noise floor figure is the criteria for good antenna.

On HF and MW, I wonder if you ever get away from the noise on the band.  It is inherent in the bands.
Maybe multi element beams or log peoridic yagis will give you low noise and highest SN ratio.
But they are not practical for MW and HF bands up to about 14Mhz.

And in real RXing environment, as I have said before will say again, there are many other factors affecting
the noise on your radio. Your RX antenna is just a receptor of the noise, and your signals are just another
type of noise.

If you are in Europe, tell me how well you can hear the low power transmitting stations in AM from South America
South Pacific and Far East Asia and Afria, and I will be able to tell you how good your antenna is.
Not FT8 or some new digi mode, because they are not strictly analogue radio signals as such.

[A.Z.]

Sorry but FT8 is not interest of me. Never have used or tried that mode.
So, I cannot tell you how effective your modded MLA30+ is with the DX map.

I don't like FT8, but I find it to be pretty useful to check if a given antenna/modification works, also since FT8 uses low power

Anyhow, on the noise floor issue, I am not sure if quieter antennas are better.

Antenna system, not just antenna, it includes the antenna, feedline, grounding... see, the point which you seem to be missing is that whatever RX antenna system should be optimized to "set the noise" that is, aside from natural noise, the system shouldn't introduce much more noise than the one internally generated by the receiver, such an antenna won't be deaf at all, on the contrary, it will give you much better performance, especially for weaker signals, it isn't about "how strong" you receive, but about signal to noise ratio

On HF and MW, I wonder if you ever get away from the noise on the band.  It is inherent in the bands.

Just to make an example, using my LLD (Linear Loaded Dipole) the average noise floor is between -110 to -130 dB, using the "stock" (unmodified) MLA-30 the noise floor is between -90 to -100 dB; this means that weaker signals will be unreadable with the "stock" MLA-30 since they'll get lost in the noise; modifying the MLA-30 I was able to bring the noise floor down to around -110 to -120 dB which, while higher than the LLD one is a good result, and now the MLA can pick up signals which it couldn't before and which the LLD pulled in w/o problems; see my point now ?

If you are in Europe, tell me how well you can hear the low power transmitting stations in AM from South America
South Pacific and Far East Asia and Afria, and I will be able to tell you how good your antenna is.

Well, one of the stations I picked up last fall (in September if I recall it correctly) was the Neumayer Station in Antarctica, signal was faint since they use a low power transmitter, but was totally readable, by the way, there's no problem in picking up broadcast stations, by the way, depending from time and propagation, although I'm more interested in other types of signals

[vinlove]

But, you know, the noise floor changes with time of day too. For example, at night, I hear a lot better with MLA30, and the random wire in the garden is very noisy with even break through from MW it is useless.

During the day, the random wire hears a lot better. All the noise disappears, and gives good reception.  The MLA30 still works fine, but it is more noisier than at nights. It also depends on the signal that you hear.  Sometimes MLA30 works far better, and other times the RW hears far better.  I couldn't pin down clearly, one is better than the other, just by measuring the noise floor coming up on the graph at just one point of time? It would be wrong conclusion to say either this one is better than the other.

[A.Z.]

But, you know, the noise floor changes with time of day too.
For example, at night, I hear a lot better with MLA30, and the random wire in the garden is very noisy with even break through from MW it is useless.

You are confusing the environmental noise floor, which depends from a number of external factors, with the antenna system "intrinsic" noise floor (which includes, for example, the nasty common mode noise) and with the local "electrosmog", while there's nothing one can do about propagation and atmospheric conditions, there's quite a lot of things one may do to reduce the "intrinsic" noise floor to a minimum; hope you'll finally understand what I'm talking about

[vinlove]

But, you know, the noise floor changes with time of day too.
For example, at night, I hear a lot better with MLA30, and the random wire in the garden is very noisy with even break through from MW it is useless.

You are confusing the environmental noise floor, which depends from a number of external factors, with the antenna system "intrinsic" noise floor (which includes, for example, the nasty common mode noise) and with the local "electrosmog", while there's nothing one can do about propagation and atmospheric conditions, there's quite a lot of things one may do to reduce the "intrinsic" noise floor to a minimum; hope you'll finally understand what I'm talking about

Everyone who uses RX antenna is under the environmental factors.  What is the point of emphasising "intrinsic" character of the a antenna, if your environment is RFI farm?
I think it is time for you open your eyes and see the real picture of the RXing = what DXing on MW and HF bands means in the real world.  Please don't get blinded by "intrinsic" noise floor garbage. RXing for MW and HF DXing means you and your radio and antennas are always under some environment, and propagation and the band condition.  You are not going to be DXing in laboratory setups. None of us are, unless you are writing some commercial reviews of the products for the media or magazines.

[A.Z.]

I think it is time for you

Ok, I'm giving up, goodbye and happy new year.

[vinlove]

I think it is time for you

Ok, I'm giving up, goodbye and happy new year.

You can also lower the noise floor figures by just lowering the input voltage on any RF amps too.
Happy New Year to you

[vinlove]

I have a dipole, and longwire with ATU and the stock MLA30, and the stock MLA30 is the best performer for the weak DX signals 90% of time. So I just let it keep working until something else better turns up.  Will try different bias-t (both modded and from more upmarket units) in the near future, and will update here with the results of course.

[vinlove]

$330 Wellbrook antenna vs. Cheap balun and wire comparison.

[ZigmundRat]

I’m glad you made the comments about this being *your* experience at *your* location with *your* equipment. It’s important to understand that there are so many variables affecting HF signals it becomes very very difficult to draw conclusions between different installations at different locations even when using identical equipment.

It was interesting to see that the SNR didn’t really change much in most cases. You appear to have significant man made noise at your location, and this is where the different characteristics of the two antennas should be evident. This noise is limiting your ability to ’hear’ on either antenna. The key thing about the loop is its ability to null out noise sources by changing its orientation, not that it is an ‘intrinsically quieter antenna’. If you were to rotate the loop to minimize the man made noise, overall your performance would improve because the SNR would improve. This could mean that the signals are ‘weaker’ but the noise is weaker still and that’s the point of the loop. It’s not about absolute signal levels.

I would expect that the Wellbrook and the MLA30 would perform similarly if mounted identically (height, orientation, feed line, etc.) even if the no signal noise floor changes due to the different preamps. It’s all about signal to noise ratio.

[vinlove]

Great points ZR.  That was what I have been trying to say to AZ all along.
A simple NF figure is not the only criteria that a antenna is better than the other antennas.

There are so many other factors affecting the performance, and the main point of having antenna is to be able to receive the signals, not having quiet noise floor.
It is good if low NF can aid in SNR, so that it makes the weakest signal audible.  But often from my experience, the low NF antennas do also kills and buries the signals too, and
this is the problem with the quiet antennas. 

I think above test is not quite fair either.  Because the real test of antennas is when trying to copy the weak signals buried in QRM and QRN.
Trying out the testing antennas by listening to some very strong signals copyable with a portable radio with whip cannot be good testing.

Again there are so many variables on that testing too, so unless all the factors are identical (even the band condition, which can change in seconds ), it couldn't be a true fair testing.

[vinlove]

Just to update my own experiments with MLA30.

I have tried a few different B-Ts from commercial active antennas and loops. They are from AOR, Spectrum Comms UK and MFJ.
When replaced the MLA30 B-T with each of those other B-Ts and received RNZI on 11725 kHz for durations of few hours.

MLA30 with each of those different B-Ts sounded with hint of quietness on reception than the stock B-T, and in the case of AOR B-T, it even gave slightly improved SNR.
But there was no significant difference in the reception quality and readability.

RNZI signal is one of the toughest to copy coming from most distance location from me, and it still all sounded very weak no matter what B-T was paired with MLA30.

When switched over to my lonwire with ATU in the garden, it was a lot better copy than MLA30 with any B-Ts.
So is it worthwhile to replace the MLA30 B-T?  For slight improvement in noise, yes.
But overall RX readability and intelligibly? I doubt it is making huge difference.

More critical factor seems, , the location of RX (Height and RFI situation) and more well matched antenna to RX.
The DXing capability antenna tests should be carried out for RXing the most tough signal to copy in terms of weakness and QRM and from most distant location.
There is no point doing antenna tests with generally strong signals coming from same continent or TXing with mega millions of kWatts, which can be copied with any radios with whip antennas. And the NF graphs and figures in lab setups? It tells about maybe the amount of noise generated by the antennas themselves, but not the capability of DX reception? Just my 2 cents. cheers 73s.

[A.Z.]

oh well

https://www.hfunderground.com/board/index.php/topic,69273.0.html

deep sigh

anyhow, I'm collecting all the infos details and pics, so may have something ready in a while, all I can say is that the high noise floor of the standard antenna is confirmed, luckily there are some workarounds which can turn it into a pretty decent antenna... more later

[edit]

Here are a couple screenshots, the 20m bands was almost dead when I took them, so they are a good example, the first pic shows the noise floor of the LLD (Linear Loaded Dipole)



while the second one shows the noise floor using the MLA-30+ with its standard bias-t unit, both antennas were placed outside at almost the same spot and height



now, while some increase in noise floor is to be expected since the MLA is an active antenna, while the LLD is a passive one, the level of noise which can be clearly seen is, in my opinion, far too high and in particular if we consider that the MLA is a loop antenna

[vinlove]

Sure. If you can improve the antenna drastically, and you can hear dx stations better, then by all means. Please let us know about it.

But from my experience and feelings, anslysing and improving HF antennas are inseparable from the factors such as what kind of RXing you do, and your Radios and RFI environment.

It seems not very meaningful just discussing the antennas without those conditions. Because, if you are just a causal listener not interested in dxing the weak signals from the remotest corners of the word with small power, then any antenna will copy most signals very well. Even the whip antenna on your portable can rx all these signals very well. And even if you are comparing the whips, longwires and the loops, they will all sound very similar.

It is only when you try to copy Radio New Zealand or any South American low powerd am stations from Europe, the antennas will make difference. And they can be then practically tested. And also your location, type of rig and RFI situations ...etc will all contribute to the performance of the antenna you are talking and testing about.

[A.Z.]

Sure. If you can improve the antenna drastically, and you can hear dx stations better, then by all means. Please let us know about it.

But from my experience and feelings, anslysing and improving HF antennas are inseparable from the factors such as what kind of RXing you do, and your Radios and RFI environment.

It seems not very meaningful just discussing the antennas without those conditions. Because, if you are just a causal listener not interested in dxing the weak signals from the remotest corners of the word with small power, then any antenna will copy most signals very well. Even the whip antenna on your portable can rx all these signals very well. And even if you are comparing the whips, longwires and the loops, they will all sound very similar.

It is only when you try to copy Radio New Zealand or any South American low powerd am stations from Europe, the antennas will make difference. And they can be then practically tested. And also your location, type of rig and RFI situations ...etc will all contribute to the performance of the antenna you are talking and testing about.

You are mixing and matching different things which are unrelated; an antenna is an antenna and can be characterized for (e.g.) its gain and pattern, an active antenna has the additional preamplifier stage, so the performance of the latter should be taken in account, this means considering the noise introduced by the preamp, its IMD characteristics and then some, then, there's also to deal with the feedline which may (and generally will) carry common mode currents and then some; you seem to keep ignoring all these and focus on "what stations" or "which frequencies" which are totally outside the discussion about the antenna system intrinsic noise optimization (reduction), so, feel free to carry on as you like and I hope you're satisfied with your antennas, but I won't follow you in such absurd discussions

best

[vinlove]

Sure. If you can improve the antenna drastically, and you can hear dx stations better, then by all means. Please let us know about it.

But from my experience and feelings, anslysing and improving HF antennas are inseparable from the factors such as what kind of RXing you do, and your Radios and RFI environment.

It seems not very meaningful just discussing the antennas without those conditions. Because, if you are just a causal listener not interested in dxing the weak signals from the remotest corners of the word with small power, then any antenna will copy most signals very well. Even the whip antenna on your portable can rx all these signals very well. And even if you are comparing the whips, longwires and the loops, they will all sound very similar.

It is only when you try to copy Radio New Zealand or any South American low powerd am stations from Europe, the antennas will make difference. And they can be then practically tested. And also your location, type of rig and RFI situations ...etc will all contribute to the performance of the antenna you are talking and testing about.

You are mixing and matching different things which are unrelated; an antenna is an antenna and can be characterized for (e.g.) its gain and pattern, an active antenna has the additional preamplifier stage, so the performance of the latter should be taken in account, this means considering the noise introduced by the preamp, its IMD characteristics and then some, then, there's also to deal with the feedline which may (and generally will) carry common mode currents and then some; you seem to keep ignoring all these and focus on "what stations" or "which frequencies" which are totally outside the discussion about the antenna system intrinsic noise optimization (reduction), so, feel free to carry on as you like and I hope you're satisfied with your antennas, but I won't follow you in such absurd discussions

best

My point is coming from real SWL activities with the real antennas MLA30, lw, and dp and gp.  It is not absurd discussions made of some imaginations.
I am not saying what you are doing is pointless. It is still interesting aspect of antenna theories and practicals.

But you must always also give data, what receivers you have used with the antennas you are working on (I asked you before, and you laughed off making it out as if it were police testing or something like that?), and data on what stations you copied , and where you are located, and your RFI environment descriptions too. If you are located in Italy, and saying that your antenna is copying great for signals from Spain, France or China (1500 kW TX power) or Romania, I would not be much impressed.
I would be impressed, if you were copying R. Clube do Para 4885 kHz, or 3310 kHz Bolivia, 4055 kHz lpam stations or the am stations from South Pacific Islands with 1 -10kW tx power or RNZI.  I would say that your antenna is really working for you, and you have done the great job for improving it etc.

And I would have some more realistic ideas about what you are doing and saying is not meaningless dream catching stories, but some more realistic practical works that can be put into the real RX antennas for HF DXing.

73s

[A.Z.]

please, explain me what the receivers I own, the antennas I use, the stations I receive have to do with optimizing the MLA-30 antenna to reduce its intrinsic noise and improve its performances

[vinlove]

When you say MLA30 is noisy, you must explain what RFI condition your environment of RX.  If you are in a high rise flat with loads people around you running many electrical devices which emits RFI, then yes, MLA30 or any shape and form of antenna will be noisy in both NF and RX.  But if you have an acre of land on the top of the high hill, with no one around you, I am sure MLA30 in the QTH would be quite acceptable in NF.

Also what radios have you connected MLA30 too. If you connect MLA30 to cheap portables with no front ends, yes, it will overload and noisy.  But if you connect it to let say some vintage tube radio, it will be very very quiet.  If you connect it to Icom R75 or NRD 525, then it would be just OK.

I could go on and on, but you get the picture. Without these extra data, antenna mods and tests are not very meaningful. That is my point.  I find MLA30 not great DX antenna from stock, but not bad either.  Trying out different B-Ts did not make much difference. So, I did not see much point trying mod it, and just use it stock.

I use it with R75 and NRD525, and try to RX all those LPAM signals from the locations I mentioned. My QTH is not too bad for RFI and I have a good garden for about 20m long wire antenna.  But as I said, if you could improve it and make better DXing antenna, that would be great. But those extra data for your mods and tests would be much appreciated.

I am saying this, because in the past, I have tried expensive and very highly reviewed antennas with great lab test results and NF figures and all the rest, but when tried in real RXing, it was not much better than my no cost longwire in the garden.  That does not mean that I am ignoring all the lab test results and NF figures on the paper at all.  They are very meaningful but when only supplement with the extra practical data from the RX.

[A.Z.]

you haven't the palest idea about intrinsic preamp/supply noise and common mode noise, do you ?

heh

[vinlove]

you haven't the palest idea about intrinsic preamp/supply noise and common mode noise, do you ?

heh

Please stop trying to be cute. It's not funny.

[A.Z.]

ok, so please, pick the MLA-30 preamp and bias-t and run a series of tests to characterize its intrinsic noise, then come back here and show your results

goodbye

[vinlove]

Sure, the most important thing with your RX antennas, what they can hear, not how quiet they are.
I am not sure, if you are doing any SWL and BCL DXing on HF.

Because if you do, you would have noticed, that even the noisy longwire can turn to very nice quiet antenna pulling good signals from DX locations depending on the band condition.
And even the most quiet antennas can turn to noisy, if there are disturbance such as sporadic E, aurora or if they are placed in strong RFI farm area, then it will wipe out your RXing totally with noise.

So, in the lab testing conditions of the antenna, I am not sure how your settings are in measuring the NF noise and all these.  Without all the factors being considered and tested, it would be quite meaningless to say, this antenna is noisy or quiet.

So, supplement with the extra practical data and it would be a lot more convincing and meaningful project.
For me, as I have told you, I have tested out a few B-Ts with MLA-30, and I couldn't notice significant improvement in pulling the DX signals I was trying to hear with all the options, hence I went back to the original MLA30 B-T.  It was just ok as is, and concluded my effort for mods will not significantly improve the DX RXing capability.
I would rather try out different antennas such as Wellbrook or EWE or Mini Beverage or verticals.

But I will keep update with what I find from own practical tests and experiments. I think your mods ideas also interesting stuff. It is just I have different ideas and point of view on it, and we can see the whole picture from different angles. I am not rubbishing your ideas and efforts for improving MLA30.  Please update with your ideas and tests and practical results, and they would be very helpful. Thanks 73s

[A.Z.]

For me, as I have told you, I have tested out a few B-Ts with MLA-30, and I couldn't notice significant improvement in pulling the DX signals

I'll repeat it for the last time, then I'll stop; the modifications to the BIAS-T are aimed at reducing the INTERNAL noise which it generates, the same goes for the other modifications; lowering the noise floor will give better reception, plus it may and usually will help pulling out very weak signals which, otherwise, would be lost in the noise; now, while there's nothing one can do about propagation, there's quite a bit of things one can do to optimize his antenna system, that's what I'm trying to do with the MLA-30, applying some cheap and easy modifications which, by reducing its internal noise improve its performances; just to say, days ago I was listening to a VK ham station on my LLD (Linear Loaded Dipole) antenna and decided to try the "stock" MLA-30, well, the station was still there but was barely readable due to the noise introduced by the BIAS-T, replacing the BIAS-T with another one I have lowered the noise and improved the readability of the signal, see what I mean, now ?

I already posted a couple images of the spectrum as seen using the LLD and the MLA and it's easy to see what my noise floor is and how, the noisy BIAS-T raises the noise floor a lot, but since that may be easily cured by either modifying the stock BIAS-T or by replacing it, it's what I'm doing (and then some more, since there are other cheap and easy mods to further improve it)

[vinlove]

I will also repeat for the last time. I am not saying the internal noise of the antenna is non relevant.
But the more over riding factors in HF Rxing are, all the points I have listed to you above.

I mean for one example out of many factors, if you connect the improved low internal noise MLA30 to 30$ portable radio, it would be very noisy and overload it.
If you connect it to a Drake R8E, then it would be great.  So, what radios are you using, I asked.

It is not just active antennas generate internal noise. The radios also generate internal noise. The atmosphere generate the noise, so do all the electric appliances you are running.
So, it is just a factor in DXing HF, but I don't feel it is a major factor. It is a minor factor from my tests with the other high quality B-Ts and MLA30.

You should keep discussing your points without emotionally upset in technical topics like this. Because we are not talking about you or me, or your or my knowledge, but just simple technical and practical facts here.

[A.Z.]

I mean for one example out of many factors, if you connect the improved low internal noise MLA30 to 30$ portable radio, it would be very noisy and overload it.

You keep changing the object of the discussion, we were talking about the MLA-30 antenna NOT about whatever receiver you connect to it, once the antenna is working at its best, there are OTHER ways to deal with some POOR receiver which gets overloaded, I understand that you're curious as for what receiver I use, well, I can make a list of some of the receivers I used, starting from my very old Geloso, to the FRG-7, IC R75, Kenwood R2000... but does this add something to this topic ? Absolutely NO, so stop trying to sidetrack the discussion and focus on the ANTENNA, not about whatever else is going down the road.

[vinlove]

Any antenna without receiver connected is totally pointless. What can you know or say about it, apart from how it looks?

If I say to you here is an antenna. Its gain is 1000 dB and NF is none.  But without connecting it to a radio, and RXing the signals coming from the live AM stations from all corner of the Earth, what can you say about it?

It is not change of the topic, but suggestion to supplement with the vital practical data, and make it more complete. That was just a suggestion, but you seem rather taking it too personally unduly over reacting to it.

[vinlove]

I now have 2x MLA30, longwire, dipole and Wellbrook ALA1530 for HF RXing.

After RXing for DX signals with all those antennas switching in-between, I cannot honestly say that noise floor figure is a major problem for DXing the weak signals on HF.

It more boils down to where the antennas are setup, where the antenna is pointing to in case of directional antennas and the band conditions.  Even more quiet antennas at one time becomes totally noisy, and vice versa. (noisy longwire becomes nice quiet Rx antenna at times)

They are all great RX antennas at one day and a time, and the next day it becomes noisy and useless, and the other antennas do better.

So with all the factors involved in HF RX and DXing,  NF figure is just a minor point, which one must take not too seriously.  If the condition is good, even a built-in telescopic whip does work well.  Other times, even the most expensive and high gain and quiet antennas turn to noise catcher.

Best thing is, to have as many different type of antennas one can manage and afford in space and budget. Switch over all the antennas for the best signals on the station you want listen to.

[unikt]

Hello everyone! I have one of these antennas and I really like it. I replaced the original antenna element with an aluminum foil covered hula hoop and I also plan to get the bias tee from a mini whip instead of the original one.

This is not why I posted however. I found this on ebay, which claims to be better than the MLA-30, I ordered one and will try it out. But I wondered what you think? Can it be better?
https://www.ebay.com/itm/AMLA150-Magnetic-Loop-Antenna-Adjustable-Gain-Low-Noise-For-FM-HA-SDR-Radio/154058572374

[vinlove]

From this test vid. I highly doubt if it will be much different performance from MLA30.


But please update us with your findings once it arrives and you have done some DXing tests with the antenna.
Thanks

[vinlove]

The reason I am skeptical on the antenna for better than stock MLA30 is that, (I am repeating this yet again )

1. There are so many other factors which influence the noise floor figures and the performance of the antennas.

2. The major points for it are,
The band condition
The Antenna set up, location (how high low or near the building or clear in the field) and environment
RFI condition (How bad RFI saturation is in the vicinity of the antenna
And even type and length of the antenna element (smaller and shorter element tend to be quieter than larger and longer element)
And the noise generation of the receivers ... etc etc.

So it is meaningless to say, oh this antenna has quiet NF figures in the lab test results, so it must be better antenna.
And how well can it copy the weakest DX signals from the most distant locations from your RX site?
Perhaps this is the most important question on the DXing antennas, be it MW LW or HF.

MLA30 with the stock B-T, and another MLA30 with high quality B-T from AOR, ok on testing environment, it seemed the MLA30 with the high quality AOR B-T sounded quieter.
But in the real RXing condition? They were similar. They were both overrun by QRM, if the band condition gets noisy. Both got noisy equally under bad RFI condition too. And copying the weak DX signals? They were kinda same, no much huge difference between the two.

So, rather than spending time and money and energy for modification, I went for just buying different type of antennas = a vertical and another Active Loop.
Time is money, and sometimes it is better to just buy different and better product than modification efforts.

[A.Z.]

So it is meaningless to say, oh this antenna has quiet NF figures in the lab test results

Do you own an SDR receiver (even a simple RTL-SDR one) ?

[vinlove]

Yeah I have a SDRPlay RSP1A.

[A.Z.]

Yeah I have a SDRPlay RSP1A.

Fine, so please, try running a very simple experiment; since you wrote you have several antennas, plug the SDR and set it to a band, say the 20m one (14MHz), connect a passive antenna and tune in to a weak signal (or even a free frequency in the band), then take a snapshot of the waterfall/spectrum, now, switch to another antenna and take another snapshot, repeat it with your other antennas, including the stock (standard bias-t) MLA-30 and, if you want, an alternate BIAS-T too, then post the pics here, it will be interesting to see them

[A.Z.]

Hello everyone! I have one of these antennas and I really like it. I replaced the original antenna element with an aluminum foil covered hula hoop and I also plan to get the bias tee from a mini whip instead of the original one.

This is not why I posted however. I found this on ebay, which claims to be better than the MLA-30, I ordered one and will try it out. But I wondered what you think? Can it be better?
https://www.ebay.com/itm/AMLA150-Magnetic-Loop-Antenna-Adjustable-Gain-Low-Noise-For-FM-HA-SDR-Radio/154058572374

first of all, I'd try running some fat copper wire or some of them in parallel inside the hula hoop, I suspect the signal may improve a bit

as for the other antenna, don't know what to say w/o a schematic, but sincerely I won't expect "stellar" performances from it

[vinlove]

Yeah I have a SDRPlay RSP1A.

Fine, so please, try running a very simple experiment; since you wrote you have several antennas, plug the SDR and set it to a band, say the 20m one (14MHz), connect a passive antenna and tune in to a weak signal (or even a free frequency in the band), then take a snapshot of the waterfall/spectrum, now, switch to another antenna and take another snapshot, repeat it with your other antennas, including the stock (standard bias-t) MLA-30 and, if you want, an alternate BIAS-T too, then post the pics here, it will be interesting to see them

No need for that.
I told you time is money.  I would rather listen to the band with my radios and antennas looking for interesting exotic DX signals, rather than fiddling about with the SDR screen captures. That is not fun.

[A.Z.]

Yeah I have a SDRPlay RSP1A.

Fine, so please, try running a very simple experiment; since you wrote you have several antennas, plug the SDR and set it to a band, say the 20m one (14MHz), connect a passive antenna and tune in to a weak signal (or even a free frequency in the band), then take a snapshot of the waterfall/spectrum, now, switch to another antenna and take another snapshot, repeat it with your other antennas, including the stock (standard bias-t) MLA-30 and, if you want, an alternate BIAS-T too, then post the pics here, it will be interesting to see them

No need for that.

I see, well, thank you anyway, your reply is still very useful and eye opening

[vinlove]

I see, well, thank you anyway, your reply is still very useful and eye opening

If the improved B-T fed Active Antennas can be also improved on DXing performance, it would be worthwhile effort to go and mod or replace the stock MLA30 B-T with better ones.  But from my testing, it was not really making noticeable difference in DXing after with better B-T paired with MLA30.  So, what is the point? I thought. I just went back to the stock B-T for the MLA30.

As day and time changes, so does the HF propagation and noise level in the atmosphere, and sometimes the longwire with tuner works better, sometimes MLA30s, and mostly the Wellbrook works better.  So, I thought have as many antennas as I can fit into my space, and use the best one for the propagation at the time. But the improved B-T NF noise figure cannot override the noise in the atmosphere and band condition. That was my conclusion.

I still would be interested to see your modded and improved MLA30 update, but with the practical test results what it was able to receive, and how it is different from the stock B-T, if you would update it.  But if not, it is OK. Thanks 73s.

[A.Z.]

As day and time changes, so does the HF propagation and noise level in the atmosphere

But not the internal noise generated by a badly designed antenna; I asked you to show your noise floor on the various antennas (it would take seconds), but you denied and you're going on talking about fried air, so I must thank you again for this post which is another good eye opener

[Co6aka]

Antenna position/orientation, "gain" and the variability of RF noise makes such comparisons challenging, to say the least. Without an anechoic chamber, the basic way to measure internal noise is to substitute an inductor equal in value to the loop (inductance and resistance) and then enclose the amp in a RF-tight box, that may have to also be grounded, depending.

But there are other factors I discovered years ago... "Feedback noise" as I call it when the antenna hears it's amplifier's output, and IMD products resulting from strong out of band signals like the VHF-TV and FM-BCB soup here in NYC. Plus, there's my local "27MHz good buddy" on his "squawk box" with the obligatory "lean-year" "footwarmer" that actually does spew RF from DC to daylight, wall-to-wall treetop-tall rightatcha-c'monback, all of which modulates the entire HF spectrum, DC to daylight, but that's an extreme example. IMD aside, when the amp's headroom is used up, it's used up, even if the amp is quiet in a chamber or a box. PLUS... Something I hadn't considered before seeing SM5BSZ's videos covering audio frequency noise causing reciprocal mixing in MMIC amplifiers; gotta investigate that too.

The LM592/NE592 used in the MLA-30 is well documented and is easy enough to model and breadboard, and from there its limitations will become clear. The AD8129/AD8130 would most likely be better, but neither make a "good" loop amplifier. To do that, you need a very low noise figure with a very low input impedance plus very high linearity plus "juice" and the ability to pump it into a 50/75-Ohm coaxial cable. This is far from trivial, and far beyond the capabilities of a jellybean opamp.

[vinlove]

yeah, this is the part of my point.

I have 2x MLA30s positioned NS and EW directions.  A Wellbrook ALA1530 and longwire.  They all perform better at different times and days for different signals.
They all have times of quiet state, and get noisy and very noisy at times.

Even if the MLA30 which may feel noisy antenna due to the design or whatever, they get very quiet and work great, while the other antennas are noisy or deaf, and vice versa.

 I concluded that noise floor figure of MLA30 is not really critical factor for being good DX antenna. There are too many other factors involved in  this game. And yes in case any Active Mag Loops such as MLA30 and Wellbrook 1530, the directivity also kicks in. If it is pointing to wrong direction from the signal you are trying to listen, it will sound poor, and it can even NULL it out.

With all these factors playing on the actual RXing and DXing the bands, I thought it would be better to put another antenna such as a good vertical or sloper and switch inbetween different antennas for the DXing, rather than trying to mod the B-T of MLA30 imagining that it would enhance or improve hearing the faint signals, because it ain't going to.

[A.Z.]

Antenna position/orientation, "gain" and the variability of RF noise makes such comparisons challenging, to say the least. Without an anechoic chamber, the basic way to measure internal noise is to substitute an inductor equal in value to the loop (inductance and resistance) and then enclose the amp in a RF-tight box, that may have to also be grounded, depending.

Hi there, let me start by saying that, willing to properly characterize a preamp, the approach you describe is totally correct, on the other hand, for a coarse evaluation of the noise floor, using an SDR and an antenna switch, to compare a given preamplified antenna with a know one will at least give you an idea of the noise floor of the preamp, since the band conditions won't change in the seconds needed to switch between an antenna and another one

That said, while the TL592 used in the MLA-30 isn't exactly a quiet amplifier, it isn't the real issue with that antenna; most of the MLA-30 noise comes from the voltage multiplier IC used in the original BIAS-T circuit, by either modding it (or replacing the whole unit); as an example, I ran a simple test tuning to the Shannon VolMet and then swapping back and forth the standard BIAS-T and another one from a miniwhip, with the original BIAS-T, the VolMet signal got lost in the noise, with the other one, the VolMet signal was readable although with a bit more noise than the one I got using my "LLD" (linear loaded dipole) antenna, but that was expected since the MLA has a preamp (and then being wideband [untuned], it's also subject to IMD in case of strong nearby signals)

What I can say is that, by replacing the BIAS-T unit (or modding it), replacing the stock RG-174 coax with better one and adjusting (lowering) the preamp gain trimmer, the performance of the MLA-30 improves quite a bit, and while it won't become a skyloop or the like, the improvement is particularly noticeable with weaker signals, then by the way, there's little one can do with propagation, but at least, after the modifications, the antenna will contribute much less to the noise level  and, all in all, it's all about setting the S/N ratio, not about gain, that's also why I prefer using passive antennas, but I was curious to try the MLA-30 so here I am

[Co6aka]

I'd build a completely new DC injector from scratch, using a isolated shield BNC for at least the antenna side with a internal coaxial common mode choke attached. I've used RG-188 and four 75-mix beads that form the four sides of a square with the coax running a few turns through them - as many turns as would fit. (I'd like to experiment with alternating 75-mix and 73-mix beads to perhaps get a wider bandwidth choking effect.)

Any noise generator should eliminated, and that DC/DC converter scheme they used is just plain double-facepalm RF design. "Linear" sourced DC-in to a good common mode choke, followed by good VLF-HF filtering. Maybe embed a low noise 12V linear regulator after that. (Maybe a steel box would be better than a aluminum box for the DC injector - less EMI coupling to the DC-injection circuitry? Or use mu-metal?)

For DC injection, use at least two shielded (wire completely enclosed in ferrite) axial chokes in series, with a lower inductance connected to the antenna-side followed by a higher inductance to the DC source. Wideband choking impedance of the combination can be swept with a spectrum analyzer or sig-gen and scope; make essentially a RLR Pi-network and sweep it. I did that for my Wellbrook and it made a big improvement from AM-BCB down to 10kHz VLF.

As for coax... I switched over to good quality 75-Ohm braid-over-foil foam dielectric copper core (center conductor) coax; currently using RG-11 from the DC injector to the antenna, and RG-59 from the injector to the radio (because it's more flexible than RG-6.) Before changing the coax from RG-58, I de-powered the antenna and tuned around 10kHz-30MHz to get an idea of how much signal ingress there was. After changing the coax I was amazed by how much less ingress I heard. (The lower capacitance of the 75-Ohm coax might improve the amplifier's output capability.)

I also added 31-mix ferrites over the coax in two places, just outside the shack and just before the antenna. Likely I also need to do this on other feedlines to nearby antennas. Ferrites over the coax between the injector and radio don't seem to make any difference.

Beyond that, work would have to be done on the loop amplifier. If you're not in a potent RF-soup environment, making the loop element (diameter) bigger might help higher frequencies as the loop impedance will increase and be a better match to the amplifier's input.

On a somewhat related note, if anyone wants to have some fun, go to a auto junkyard and get some of those sharkfin antennas and experiment with the E-field. Supposedly they use a ASIC, which makes me wonder if it would be possible to do the same for a loop amp.

[A.Z.]

well didn' t go as far as totally rebuilding the injector (although it won't take much time), I had a RA0SMS miniwhip bias tee unit at hand, so I just used it, and it worked, the original unit isn't bad ... but that voltage multiplier totally screws the design

A thing which I didn't yet try is adding a (say) 16:1 or the like transformer between the loop and the preamp input, the idea is to get a better impedance match over the frequency range

as for the coax, the "RG174" which comes with the antenna is something one would never use, it's ok to wind a choke (18 turns around an FT140-43 core) but... nothing more, a run of decent coax, even RG58 (or 59) or some tv/sat cable will work MUCH better

Overall, for its price, the MLA-30 once properly modded/adjusted isn't a bad antenna, in particolar for space constrained installattions, but one should keep in mind that, to have something working decently, ut needs some tweaking...

and, btw, that's the fun

[Co6aka]

Of possible interest... This morning the following message was posted to some of the GROUPS.IO mailing lists:

If any one is interested I just finished building 5 more LZ1AQ loop amplifier boards with bias tees. These will be the last I build for awhile. The performance of this Improved version on the LZ1AQ is much better than the original design. For info and prices you can contact me off list, at everettsharp@aol.com..

I use this loop amplifier here at my QTH for my SDR receiver for coverage from 100kHz to 30MHZ and it is my best RX antenna.

Everett N4CY

I have no connection with that poster, just passing it along because the LZ1AQ loop amp is a much better alternative. I have one and have experimented with it quite a bit, though I'm not using it now.

[A.Z.]

Thank you "sobaka"

Yes, the LZ1AQ and the WellGood (Wellbrook clone) are both good

http://www.lz1aq.signacor.com/docs/wsml/wideband-active-sm-loop-antenna.htm

https://www.george-smart.co.uk/projects/wellgood_loop/

but, see, the purpose for this discussion (set aside the sidetracking attempts) was/is to "hack" the cheap MLA-30 and improve its performances w/o spending too much, sure, the final result won't probably be up to par with other circuits, yet, I believe that, with some easy/cheap (that's the unwritten rule of this "game") mods, the MLA-30 may become a good pick for people willing to start with SWLing and not willing to invest an arm and a leg

[etkal]

I have a great solution to allow you to feed 12v into the Bias Tee and bypass the noisy micro USB 5v step-up.

Looking at my board, it doesn't quite match the circuit, in that the last component prior to the DC choke is the LED and its resistor.  Cutting the trace just before that (to the right), separates the voltage boost from the output.  You can then add a 12v input across the DC choke pins 2 and 3.  I used a 5.5 x 2.1mm DC cord and plug.  This keeps the LED and the choke in the circuit.

In order to restore the micro USB capability, I added a 12v jack to the side, and jumpered the 12v+ contact on that to the other side of the cut trace; there is an unused pad that works nicely.  Nothing is necessary for the negative contact.  Plugging the 12v plug into the jack then basically shunts from DC choke pin 3 back across the trace to complete the original circuit.

  73, Erik W1QED

[A.Z.]

Hi Erik, that's almost what I did too, then I also lowered the preamp gain using the unpotted trimmer found on the preamp board and adjusted the trimmer inside the bias-t unit for no attenuation (lowers noise a bit too); at the moment I'm using the preamp with a 18m perimeter wire loop with pretty good results, I also wound an isolation transformer (1:4 impedance ratio) placed between the loop and the preamp, that helped improving things a bit on some bands (like the 15m one), all in all it isn't so bad given its cost, then ok the noise floor isn't as low as the one from other units, but given the cost ...

[clytle374]

Hi Erik, that's almost what I did too, then I also lowered the preamp gain using the unpotted trimmer found on the preamp board and adjusted the trimmer inside the bias-t unit for no attenuation (lowers noise a bit too); at the moment I'm using the preamp with a 18m perimeter wire loop with pretty good results, I also wound an isolation transformer (1:4 impedance ratio) placed between the loop and the preamp, that helped improving things a bit on some bands (like the 15m one), all in all it isn't so bad given its cost, then ok the noise floor isn't as low as the one from other units, but given the cost ...

Thank you for this information, you saved me from wasting my time trying to get more gain out of this amplifier to compensate for a weak receiver.  Also the bias T is definitely a poor design.  Thanks for the heads up about using the sdrplay's internal bias T and it's lower voltage.  I'd also like to nominate you for the most calm and patient user award

[A.Z.]

Thank you for this information, you saved me from wasting my time trying to get more gain out of this amplifier to compensate for a weak receiver. 
Also the bias T is definitely a poor design.

You're welcome, again, I don't pretend that the MLA-30 could "magically" become some Wellbrook or the like, yet given its low cost, it's possible to somewhat "remediate" to some of the design flaws and squeeze a bit better performance out of that loop; to recap

1. Modify the bias-t unit to exclude the voltage multiplier, feed the unit with 12V from a good PSU and set the attenuator trimmer inside the bias-t to "zero attenuation"

2. Add a BNC connector to the preamp unit and replace the coax with good quality one, keep the original coax (inside the box, from the preamp to the connector) a bit longer and use it to wind a CMC choke on an FT140-43

3. adjust (lower) the gain of the preamp to obtain good signal but keep the noise floor as low as possible

4. add a 1:x transformer (experiment with the ratio, 1 to the loop, x to the preamp input) between the loop and the preamp, the transformer will be hosted inside the preamp box

Thanks for the heads up about using the sdrplay's internal bias T and it's lower voltage.

Using the internal BIAS-T of some SDR units will work, but performance will degrade since the reduced voltage (about 5V) will also reduce the dynamic range

I'd also like to nominate you for the most calm and patient user award

LOL !! Nothing special, one may, sometimes, loose patience in real life; but it makes no sense to me loosing patience in a forum discussion

[clytle374]

Horrible and quick hack to remove most of the switching noise from the power supply ending up in the antenna lead.  Nearly offensive practice, but it is temporary and helped a lot.

[A.Z.]

Horrible and quick hack to remove most of the switching noise from the power supply ending up in the antenna lead.  Nearly offensive practice, but it is temporary and helped a lot.

Well, that's pretty extreme ! Didn't the modifications shown here

https://www.eevblog.com/forum/rf-microwave/mla-30-active-loop-antenna/?action=dlattach;attach=1126610;image

suffice ? Those mods exclude the voltage multiplier IC from the circuit, at that point you'll power the unit using 12V DC from a clean supply connected to pin 1 (+VDC) and 5/6 (GND) of the USB socket (which won't be used anymore and could be removed and replaced with a different connector - or either you may pass a red/black wire out from the connector hole)

As a note, I've been using for almost one year now the MLA-30 preamp connected to a horizontal wire loop (about 18m total) and it's working well, all I did was adjusting the preamp gain by using the trimmer found inside the preamp box to avoid overloading (by the way the preamp box was modified by adding a BNC connector and a choke inside the box), the whole thing is fed using a run of "RG6" (tv/sat) double shield coax

[clytle374]

Yes, but that required my digging through boxes to find a  12V wallwart.  This took 15 minutes and still runs off USB.  I'm building a new loop and amplifier anyway, and this honestly felt more vengeful.  Lol

[A.Z.]

Yes, but that required my digging through boxes to find a  12V wallwart.  This took 15 minutes and still runs off USB.  I'm building a new loop and amplifier anyway, and this honestly felt more vengeful.  Lol

As for the loop, if you didn't yet choose a design, have a look at this one

https://www.larches-cottage.co.uk/rx_antenna/loops_rx/Evaluating%20a%20Broadband%20Active%20Loop%20Antenna.pdf

then, for the preamp, you may also consider a remotely tuned one, like the one found here

http://www.arrl.org/files/file/QEX_Next_Issue/Jan-Feb2018/Steber.pdf

[clytle374]

As for the loop, if you didn't yet choose a design, have a look at this one

https://www.larches-cottage.co.uk/rx_antenna/loops_rx/Evaluating%20a%20Broadband%20Active%20Loop%20Antenna.pdf

then, for the preamp, you may also consider a remotely tuned one, like the one found here

http://www.arrl.org/files/file/QEX_Next_Issue/Jan-Feb2018/Steber.pdf

Thanks, I bookmarked and will read tomorrow, been soldering 402 components on my limesdr for the last 3 hours modding the input circuit for HF.  My nerves are shot, and I managed to lose a part to other other antenna port, soldering through a jeweler's loupe.  I'm getting decent performance now, that and a DIY LPF to keep the FM broadcast out of it.

I was following a webpage https://www.lz1aq.signacor.com/docs/wsml/wideband-active-sm-loop-antenna.htm  I think it was recommened here, but not sure anymore.  RF is out of my comfort zone, but if you know what you're doing, you're not learning anything is a motto of mine.  Is this forum tolerant of stupid questions?  I asked on some FB groups and people don't know. Probably start a thread here and see how it goes.

Thanks, Cory

[A.Z.]

As for the loop, if you didn't yet choose a design, have a look at this one

https://www.larches-cottage.co.uk/rx_antenna/loops_rx/Evaluating%20a%20Broadband%20Active%20Loop%20Antenna.pdf

then, for the preamp, you may also consider a remotely tuned one, like the one found here

http://www.arrl.org/files/file/QEX_Next_Issue/Jan-Feb2018/Steber.pdf

Thanks, I bookmarked and will read tomorrow, been soldering 402 components on my limesdr for the last 3 hours modding the input circuit for HF.  My nerves are shot, and I managed to lose a part to other other antenna port, soldering through a jeweler's loupe.  I'm getting decent performance now, that and a DIY LPF to keep the FM broadcast out of it.

I was following a webpage https://www.lz1aq.signacor.com/docs/wsml/wideband-active-sm-loop-antenna.htm  I think it was recommened here, but not sure anymore.  RF is out of my comfort zone, but if you know what you're doing, you're not learning anything is a motto of mine.  Is this forum tolerant of stupid questions?  I asked on some FB groups and people don't know. Probably start a thread here and see how it goes.

Thanks, Cory

Hey Cory, the LZ1AQ is a very good preamp, so if you're building it... go for that, I thought you didn't yet start the build, so I offered those links to give you some ideas, but the LZ1AQ is definitely a good preamp

[clytle374]

Hey Cory, the LZ1AQ is a very good preamp, so if you're building it... go for that, I thought you didn't yet start the build, so I offered those links to give you some ideas, but the LZ1AQ is definitely a good preamp

I'll go ahead an venture off topic a bit. Between that amplifier and a video by a mikrowave1 youtube channel. I decided to go with the LZ1AQ amplifier and loop.  The issue I have is this SDR's sensitivity drops off pretty bad at the low end of HF.  The mod I just completed helps a lot, but still pretty bad below 10Mhz. The LPF I built keeps the FM broadcast out of it since it's very sensitive up there.  I'm currently actually getting the AM broadcast band and 160M okay.  I did do the opposite of the good thing and turned the gain up on the MLA-30.   So I decided to slightly mod the input of LZ1AQ's amplifier with a first order LPF trying to counter the slope of the SDR slope, and the output for more gain.

I need more gain.  The mikrowave1 video "loop amplifier #3" also used the 180 ohm 'swamping resistors' to lower the output impedance of the output stage.  I don't know how to calculate the output impedance of a common emitter into a transformer. I did google it to death. But mikrowave1 said a 9:1 impedance would be better than the resistors.  So I decided they both we close to the same, even though mikrowave1's were only common base circuits.  LZ1AQ didn't specify a toroid material. 

So I threw the semi-educated guess at it and used a T50-2 core, twisted 7 windings, and got 19 turns before it was full.  I needed 20 turns to get LZ1AQ's inductance specs iirc. I put 6 windings in series with a CT, and a single winding for the output.  Testing 1 turn to 1 turn gave me this.
Picture 1
I then built it on a breadboard, just to see what I would get.  I didn't build the lowpass on the breadboard.  And I guessed how to couple 50 ohm output of my SA TG to the low impedance of the amplifier.  Used 6 turns on a t50-2 core with the input passed through the core.  2.5:1 turns sounded right, but didn't work much.   
Picture 2
I got this, only want to got to 50Mhz, and this is a breadboard so I have not faith in the numbers.
Picture 3
So I'm confused about the impedance.  The 9:1 output seems to be a voltage loss, when I need a gain.  But all the current is passing through the transformer this way.  Any advice? Should I start a thread here? Or will I get ripped apart?  Fastest way to swim is jump in the deep end.  If this project isn't doomed due to my ignorance, I'm going to make a PCB tomorrow. 
Thanks, Cory

[A.Z.]

regarding the LZ1AQ preamp, check here

https://easyeda.com/3ym3ym/LZ1AQ-loop-preamp-SMD_copy

as for the remainder, go on and open a new thread, add full details and clearly specify your questions and doubts

[A.Z.]

Also, I'm a big fan of the "step by step" approach and also of the "don't add stuff if it isn't needed" one so, in your case, I'd start with a plain vanilla PASSIVE loop as the one described here

http://www.kk5jy.net/rx-loop/

and build the loop and the needed impedance transformer, done that, in case you'll want to add a preamp, doing so will be easy since ANY preamp accepting an impedance around 50 Ohm will fit; more, adding that "tuned preamp" (see my previous post), would result in a tuned preamplifier (which thanks to the varactor tuning may be remotely controlled) which not only will boost the signals from the loop but may also help avoiding the various "bandstop" filters

[clytle374]

as for the remainder, go on and open a new thread, add full details and clearly specify your questions and doubts

Thanks again.  I'm going to read the links you sent. And do a little more research and I'll start a post.  A passive loop will leave me completely deaf below 8mhz.  Varactor options had crossed my mind.  THe plan is for this to be my monitor when I finally get a transmitting mag loop built.  And either learn CW and use the HW-16 I just rebuilt, or rebuild the HW-101.  On the plus side the amplifier on the breadboard with a 2 foot loop was picking up 20 meters in the basement. 

[7danny]

at the moment I'm using the preamp with a 18m perimeter wire loop with pretty good results

Am I reading this right? That's almost 60 feet?

[A.Z.]

at the moment I'm using the preamp with a 18m perimeter wire loop with pretty good results

Am I reading this right? That's almost 60 feet?

yes, laid horizontally in a triangular shape at about 9m from ground, works pretty well

[A.Z.]

Beyond that, work would have to be done on the loop amplifier. If you're not in a potent RF-soup environment, making the loop element (diameter) bigger might help higher frequencies as the loop impedance will increase and be a better match to the amplifier's input.

revamping this old thread due to some recent "experiments"; if you have an MLA-30 around, try the following:

build a cross shaped structure using non conductive material (e.g. PVC pipes, wood sticks...)

use the cross to support a diamond shaped loop, made using 2.5 mm wire and having 76 cm sides

connect the MLA preamp at one of the side corners of the antenna, routing the coax along the horizontal arm and then down along the vertical support

at the opposite side corner place a 530 Ohm resistor

install the antenna at about 3m from ground (or ground plane), possibly, for testing, place it in a garden or yard

aim the preamp box corner at the desired receiving direction and start listening

turn the antenna 180° and check the effect

note: willing to build a passive version or to use a different preamp, place a 9:1 galvanic transformer at the feedpoint and connect the coax or whatever preamp after it (the 50 Ohm match after the 9:1 will be almost perfect)