MLA-30+ (refrain)

[A.Z.]

Have been fiddling a bit with that "Chinese loop", and have some more infos which may be of help of people using it

First of all, "as is", the MLA is a decent performer on the BC bands and on the lower HF bands, noise floor isn't as low as it could be, but that's easy to cure, then... I had some mailing with some people I know and which are far more expert than me, and they suggested to replace the antenna loop with 8..10 turns of insulated wire to form a loop of about 60..100cm (a hula hoop used as the former will just be fine), and add a 2:1 transformer between the loop and the preamp; didn't yet try it, but judging from some "spice" simulations a friend was so kind to run, such a modification would allow an almost flat response (from the antenna) ranging from around 100KHz to about 100MHz... which isn't definitely bad; but since I was at the same time fiddling with an horizontal loop (triangular, base 9m, height 50cm, sitting at 9m over ground - yes a squished triangle) and since I wasn't satisfied with it, I decided to try a "Frankenstein style" transplant, so I connected the MLA-30 preamp box to the horizontal loop using a short run of 600 Ohm line I had around; the test of this config is still running, and I'll need to characterize it some more, but at a first look, the configuration seems to be doing fine, so in case someone has one of those around and has some room to put up an horizontal loop (at some height, the horizontal ones NEED it), it may be worth a try

[edit]

The attached map shows the spots picked up in 2 hours by the antenna (FT8 on 20m), I use FT8 for coarse characterization, later and on the weekend I'll also test it "in person"

[A.Z.]

just in case, if someone is interested, below is the 4NEC2 model for the loop I'm using connected to the MLA preamp

Code: [Select]


CM simple horizontal deltaloop antenna
CE

' *** symbols
SY hgt=9            ' height from ground
SY arm=4.5          ' arms to feedpoint
SY dpt=0.50         ' height of triangle
SY slp=0.25         ' slope from feedpoint
SY rad=0.0125       ' wires radius
SY tst=7.050        ' test frequency
SY seg=81           ' number of segments for each wire

' *** geometry of wires (wireid,segments,x0,y0,z0,x1,y1,z1,radius)

' left side of triangle
GW   1  seg       0   -dpt      hgt    -arm    0  hgt+slp  rad

' right side of triangle
GW   2  seg       0   -dpt      hgt     arm    0  hgt+slp  rad

' base of triangle
GW   3  seg    -arm      0  hgt+slp     arm    0  hgt+slp  rad


' *** ground parameters
GE  -1
GN  2  0  0  0  13  0.005

' *** wires loading
LD  5  1  0  0  58000000
LD  5  2  0  0  58000000
LD  5  3  0  0  58000000

' *** feedpoint
EK
EX 0 1 1 0 1. 0  0

' *** initial frequency
FR 0 0 0 0 tst 0

' *** end of model
EN



[A.Z.]

Let me start by saying that I don't like FT8, yet I find it an useful "tool" to evaluate the performances of antennas, in particular since receive sessions may be run in a totally automatic way, which allows to run them for extended intervals of time, that said...

Sounds like that horizontal loop, feeding the MLA-30 preamp is working decently well, at least judging from the spot I was able to pick during my latest test, I think that picking up signals from the Neumayer station in Antarctica (DP1POL) isn't bad for a simple, cheap antenna like that 

[A.Z.]

And since I'm at it, here are a couple images from the very first installation of that loop; later on I modified the MLA-30 box adding a BNC connector and a choke and feeding it with RG-58 coax, the next modification will be replacing the loop wire (about 18m total) with 3-conductors cable and connect the conductors in series (linear loading) so obtaining an "electrical" length of 54m, the idea is to try improving performances at the lower frequencies, I'll probably start testing that modification with a 4:1 balun (homebuilt dual core guanella) at the feedpoint and later on using the MLA-30 preamp, just to see if the preamp will be needed (I prefer going passive, if possible) oh, and the antenna is almost invisible, which isn't bad 

[vinlove]

From my testing, MLA30 high noise comes from the antenna amp itself.
Not from the B-T.
I tried with various different B-Ts to feed my MLA30+, and the NF has
not changed that much or noticeable amount.

[vinlove]

Does MLA30 not overload with what looks like longer elements?

[A.Z.]

Does MLA30 not overload with what looks like longer elements?

I was worried about it, but it doesn't seem to be the case, also since, amongst other modifications, I adjusted the gain trimmer (inside the preamp box) and lowered the gain; as for the noise, the main source is the original Bias-T, then, to further lower the noise one will need some further modifications; sure it won't be a true LNA, but with a bit of care performances will be decent and the higher noise floor will be noticeable only on some bands ... but I plan to deal with that too

[vinlove]

I have replaced one of my MLA30+ element to a hulahoop sized one, and it overloads on some frequencies.  On others OK.
No noticeable improvement on any thing with the replacement.

As I said, I tried various different B-Ts with the MLA30+, but no much difference in the noise.

I have now set up 2x MLA30+,  30m long wire with 9:1 balun and 3x Wellbrook Loops all facing different directions in the garden.

They all have weaker and stronger frequencies.  But generally the MLA30s are more noisy.
The Wellbrooks are working great with less noise, but even they get noisy at times for certain bands.
But they always outperform the MLA30s.

I was quite surprised to find how quiet and well performing the longwire and 9:1 balun is. Again on some bands and frequencies.
Now really time for listening the actual bands.

[A.Z.]

I have replaced one of my MLA30+ element to a hulahoop sized one

nice, so now, instead of hijacking or trying to troll, just hush away, goodbye.

[vinlove]

I have replaced one of my MLA30+ element to a hulahoop sized one

nice, so now, instead of hijacking or trying to troll, just hush away, goodbye.

You must have a huge chip on your shoulder. Troll? Hijack?
I was just trying to give you some wider perspectives on the topic.

[A.Z.]

ok, in such a case, instead of talking about fried air, please post some pics of your antennas and screenshots showing the waterfall/spectrum of your SDR on the 20m band and on others too if you like (it would take minutes to accomplish), those may be of help

[vinlove]

yeah, when time is available I might do that.  But I just feel that it is not really meaningful action of uploading the screen captures waterfalls and etc.
Because what it really boils down to is at the end of day, can you hear the weak tough copy DX signals well? Can you make out what they are saying?  Not the waterfalls or NF figures.  Please never waste your time and others time by testing radios or antennas by copying the strong signals, like some folks do in youtube. They are totally pointless.
20 bucks portable radios can copy these signals without any antennas.

If you are in Europe, try to copy at least the signals from the other continents such as NA, SA or ASIA or Pacific and low powered signals (under 10kW) on the HF and MW.
And please don't bother with FT8 or some digital modes, because they will get through anywhere with any piece of wire as antennas.  Try using AM or SSB or CW, the traditional modes for the testing.

There had been cases when good NF figures and good signal heights and waterfalls, but no audio or garbage content.  But there had been also cases when high NF figures and low signal levels but the audio was actually ok to listen to.

There are so many factors involved in this, so I wonder if it would be so clean simple to say, this is it. 

But of course, I am not saying that your attempt to improve MLA30 is meaningless. All I am saying is, please also consider other factors in this game.

[A.Z.]

come back when you'll have some real world informations, fried air isn't interesting and it stinks; till now you only produced a lot of chatter and no proof, and while I gave you the benefit of doubt, now it's clear that you're talking about imaginary stuff

[joeqsmith]

ok, in such a case, instead of talking about fried air, please post some pics of your antennas and screenshots showing the waterfall/spectrum of your SDR on the 20m band and on others too if you like (it would take minutes to accomplish), those may be of help

come back when you'll have some real world informations, fried air isn't interesting and it stinks; till now you only produced a lot of chatter and no proof, and while I gave you the benefit of doubt, now it's clear that you're talking about imaginary stuff

I've never heard the phase.   I suspect in the USA it would mean something like "you're full of hot air"   or that's a bunch of BS, bull or talking shit. 

Adjective. full of hot air (comparative more full of hot air, superlative most full of hot air) (idiomatic) Talking a lot, especially without saying anything of value or meaning. Did the salesman tell you anything new, or was he just full of hot air? 


So I Googled it and came up with an Italian restaurant selling ozone a few years ago.   


https://www.odditycentral.com/foods/italian-restaurant-serves-fried-air.html

[A.Z.]

fine, now, how does all this relate to that cheap mla-30 preamp modifications ?

[joeqsmith]

fine, now, how does all this relate to that cheap mla-30 preamp modifications ?

That's a very good question.  I wasn't sure why you kept using the phase as I saw no relevence and was hoping you would explain in real world terms how it fit in.

[A.Z.]

the "phase" ? ok, maybe it's the usual language barrier at work, anyway, look at my  previous mla30 related discussions and at my posts; compare them and make an educated guess

[joeqsmith]

the "phase" ? ok, maybe it's the usual language barrier at work, anyway, look at my  previous mla30 related discussions and at my posts; compare them and make an educated guess

I did and posted it above but it seems like you missed it so I will copy it again for your convenience.

I suspect in the USA it would mean something like "you're full of hot air"   or that's a bunch of BS, bull or talking shit. 
Adjective. full of hot air (comparative more full of hot air, superlative most full of hot air) (idiomatic) Talking a lot, especially without saying anything of value or meaning. Did the salesman tell you anything new, or was he just full of hot air? 

[A.Z.]

I doubt so, I was referring to

https://www.eevblog.com/forum/rf-microwave/mla-30-active-loop-antenna/

[joeqsmith]

I doubt so, I was referring to
https://www.eevblog.com/forum/rf-microwave/mla-30-active-loop-antenna/

It looks like you had a pretty decent start and your last post was recent.  Why start over with the same subject?  Or, at least why not reference it in your first post here?   Just curious.

...
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?
...

1. static and nearby tx

I understand many radio hobbyist have damaged their low cost VNAs from what they believe is static.   With the low frequencies they typically operate, I wonder why they don't add at least an external clamp.   Doesn't seem like it would be too difficult to add some basic protection.   In their application, it seems they really only want to measure SWR anyway so a bit of loss is no big deal.     

[A.Z.]

as for the reference, my bad, guilty !

as for the remainder, since I was here, I just tried to help (for the lil I can), nothing more, is it a violating rules ?

[joeqsmith]

as for the reference, my bad, guilty !

as for the remainder, since I was here, I just tried to help (for the lil I can), nothing more, is it a violating rules ?

Not that I am aware of.  Why do you ask?  Is something concerning you? 


Looking at the schematic member Co6aka posted where they show D1 and D2 diodes on the front end, any idea what they are using?    In your pictures above, I wonder if static really poses much of a problem.   Have you damaged one of the amplifiers with the antenna mounted as you show? 

[vinlove]

From my extensive testing, best improvement for the MLA30s were adding, isolating transformer and adjustable attenuator between the antenna and radio.
The MLA30+ became super quiet DX active loops.

Something like this in this video. He is using Active Mini Whip, but the same principle with MLA30.

[A.Z.]

Looking at the schematic member Co6aka posted where they show D1 and D2 diodes on the front end, any idea what they are using?

no, sorry

In your pictures above, I wonder if static really poses much of a problem.   Have you damaged one of the amplifiers with the antenna mounted as you show?

No issues till now, and if it goes "poof" no problem, I initially bought that MLA-30 to help a friend which got one improving it, but then since I was at it, I decided to try modding the thing a bit and, while it isn't the best preamp in this world, with a bit of adjustment and a better loop it seems to be working pretty well; got Antarctica several times now, and then it works fine on HF bands and BC ones too, although, to be honest, I prefer "passive" antennas and the plan, as soon as possible is to put up a linear loaded loop feeding it through a balun and w/o any preamp, I'm really curious to see how it behaves (ran some 4NEC2 simulations, but the "real thing" is usually different )

[vinlove]

In my testing and observation on the different Active Loop antennas for many weeks and even a few months now, it is impossible to get constant Noise Floor figures from any of them, because they are affected by time of the day, the band condition, and the location of  the antennas (even difference of a foot in height and distance from the surrounding objects), and RFI condition of the antenna proximities in the environment. I am sure the weather on the day affects too.
So, it seems pretty meaningless to say, this Active Loop antenna has such and such quietness and noise floor figures( which will be totally different in a few hours or tomorrow). It is far better to say, what stations it was hearing.