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Hi All,
I got the MLA-30 that Matt provided working on the bench, but quite a lot of the components were damaged during the "de-gooping" process.
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However, I've manged to measure all the component values and have been able to work out the circuit.
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The input low pass filters were particularly badly damaged and I've had to by-pass those for the time being.
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Unfortunately the 30MHz input low pass filters are designed for a 50 Ohm input and output impedance, and when used in this circuit with a low value of source impedance and a high value of output load impedance, the response curve is anything but flat.
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I also noticed that while testing the common mode rejection by shorting the two inputs together, the circuit would oscillate and produce a -10dB signal at around 160MHz. So it isn't unconditionally stable, but this may not happen (or it may happen at another frequency) if the low pass filters were in circuit.
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Gain?
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Max 30dB
Min 10dB
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Input impedance
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1.5K Ohm at 1MHz
1.4K Ohm at 10MHz
600 Ohm at 20MHz
450 Ohm at 30MHz
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OIP2 approx +46dBm
OIP3 approx +20dBm
PSAT approx -3dBm
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Common mode rejection
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PCB ground as reference approx 20dB
Coax screen as reference? ? ? ? ? ?>55dB
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Noise figure approx 12dB
Bottom line
I don't understand why they added a 5V to 12v DC to DC converter in the bias tee, other than to try and physically copy the Nti loop, so that folks think they are getting the same design.
However, you do get a lot of hardware for your money, but the overall performance is pretty mediocre.
I think the very simple two transistor "Improved M0AYF" is likely to be a better performer (though not 'stellar'), as the MLA-30 IMD figures are dire.
Circuit to follow
Regards,
Martin - G8JNJ
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Here's the provisional circuit of the MLA-30 loop amplifier.  Regards, Martin
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Thanks for sharing with us, Martin.
73, Carlos VK1EA
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On Saturday, September 28, 2019, Martin via Groups.Io <martin_ehrenfried= [email protected]> wrote: > Here's the provisional circuit of the MLA-30 loop amplifier. > > </mail/u/0/s/?view=att&th=16d735567ae239e5&attid=0.1&disp=emb&realattid= [email protected]&zw&atsh=1> > > Regards, > > Martin > _._,_._,_ > ________________________________ > 开云体育 Links: > > You receive all messages sent to this group. > > View/Reply Online (#12724) | Reply To Group | Mute This Topic | New Topic > > ________________________________ > Please trim replies, do not reply directly to a DIgest. Be kind. > ________________________________ > Your Subscription | Contact Group Owner | Unsubscribe [ carlos.peco@...] > _._,_._,_
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I read here that someone de-potted a module and there was slight damage to the circuit within. In the past, acetone has worked well for me as an epoxy solvent. Submerge the potted module a couple days at room temperature. The epoxy crumbles off and if necessary can be encouraged with a wooden stick.
Dale NX8J
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HiAll, It was Matt, M0LMK who de-potted the PCB by boiling it, and then sent it to me to try and measure the performance.
Today, I managed to repair the amplifier and get it fully running.
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As I suspected, the badly mismatched 30MHz input low pass filter messes up the frequency response. The designer has really slipped up here by using a filter designed for 50 Ohm termination impedance, but with a low impedance loop as the source and an amplifier having an input impedance ranging from 1.5K Ohm to a few hundred Ohms, as the load the response curve is all over the place.
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The following graph was taken with a low value of source impedance in order to better simulate a loop. 
I tried adding various values of terminating resistors between the amplifier chip Pin 1 and the PCB ground and Pin 8 and the PCB ground to try and improve the match, and it looks like 75 or 100 Ohms is about the optimum (50 Ohms rolls the gain off too rapidly at 30MHz) however it does reduce the overall gain, but this can be increased in order to compensate.
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The big problem is that under certain conditions the unmodified amplifier can have a 20dB higher level of gain at around 7MHz, which is bad news, especially in Europe, as this is where all the very strong broadcast stations appear at night.
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The next stage is to draw out the bias tee circuit and then try the loop outside to see how it actually performs at my location.
Regards,
Martin
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Been there, tried that Dale. I've de-potted
most things and have a number of techniques, boiling seemed the best
solution this time around. I could have probably done a better job if I
went a little slower but I wasn't that worried about saving the board.
Matt
M0LMK
Dale Lamm wrote on 28/09/2019 05:45:
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I read here that someone de-potted a module and
there was slight damage to the circuit within. In the past, acetone has
worked well for me as an epoxy solvent. Submerge the potted module a
couple days at room temperature. The epoxy crumbles off and if necessary
can be encouraged with a wooden stick.
Dale
NX8J
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You're doing great work there Martin.
Interesting to see the performance data and that crazy response curve!
Very much appreciated.
Matt
M0LMK
Martin via Groups.Io wrote on 28/09/2019 17:08:
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HiAll,
It was Matt, M0LMK who de-potted the PCB by boiling it, and then sent it
to me to try and measure the performance.
Today, I managed to repair the amplifier and get it fully
running.
?
As I suspected, the badly mismatched 30MHz input low pass filter
messes up the frequency response. The designer has really slipped up
here by using a filter designed for 50 Ohm termination impedance, but
with a low impedance loop as the source and an amplifier having an input
impedance ranging from 1.5K Ohm to a few hundred Ohms, as the load the
response curve is all over the place.
?
The following graph was taken with a low value of source
impedance in order to better simulate a loop. 
I tried adding various values of terminating resistors between the
amplifier chip Pin 1 and the PCB ground and Pin 8 and the PCB ground to
try and improve the match, and it looks like 75 or 100 Ohms is about the
optimum (50 Ohms rolls the gain off too rapidly at 30MHz) however it
does reduce the overall gain, but this can be increased in order to
compensate.
?
The big problem is that under certain conditions the unmodified
amplifier can have a 20dB higher level of gain at around 7MHz, which is
bad news, especially in Europe, as this is where all the very strong
broadcast stations appear at night.
?
The next stage is to draw out the bias tee circuit and then try the
loop outside to see how it actually performs at my location.
Regards,
Martin
?
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Here's the MLA-30 Biasing Tee circuit, as promised.  Regards, Martin
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Hi Martin,
Based on the info that you have posted it looks like the MLA-30 is not a very good loop amplifier and the Modified M0AYF and LZ1AQ loop amplifiers are far superior to the MLA-30.
Everett N4CY
In a message dated 9/30/2019 4:59:20 AM Central Standard Time, martin_ehrenfried@... writes:
Here's the MLA-30 Biasing Tee circuit, as promised.  Regards, Martin
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Hi Everett, Well it 'sort of works' and it doesn't cost very much, so it's better than nothing for folks who don't want to build their own. You get quite a bit for your money, and it's OK for use with say and RTL dongle in direct sampling mode, but I'll probably cry the first time I see one being used with a high end receiver like a Perseus or Airspy HF :-( Here are some measured parameters of various loops using the same test setup.
MLA-30? ?OIP2 approx +46dBm?OIP3 approx +20dBm
M0AYF OIP2 approx +75dBm OIP3 approx +27dBm
Wellgood OIP2 approx +57dBm OIP3 approx +37dBm
LZ1AQ OIP2 approx +79dBm OIP3 approx +36dBm
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I've now added the MLA-30 information to my Active antennas webpage.
Regards, Martin - G8JNJ
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Hi All,
Well despite the rain I put the MLA-30 up in the air today.
It's a pretty poor performer, as the noise floor is about 20dB higher than any other active antenna I've tried, and increasing the amplifier gain doesn't help improve the Signal to Noise ratio.
There's also a lot of unwanted noise around 60 & 120KHz emanating from the DC-DC switcher in the Biasing Tee.
I've left it connected to one of my KiWi SDR's so that folks can try it for themselves.
You can use my other KiWi with a Loop on the ground as a reference.
Based on my tests, I wouldn't recommend it.
Regards,
Martin - G8JNJ
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Hi Martin,
Big thanks to you for all the work on this, and of course to Matt for de-potting it, and to Jef for figuring out the type of IC being used. (The UA733 would also work, possibly a little better.)
I just got my MLA-30 couple days ago too.
73,
Steve AA7U
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On 9/30/2019 8:22 AM, Martin via Groups.Io wrote: Hi All,
Well despite the rain I put the MLA-30 up in the air today.
It's a pretty poor performer, as the noise floor is about 20dB higher than any other active antenna I've tried, and increasing the amplifier gain doesn't help improve the Signal to Noise ratio.
There's also a lot of unwanted noise around 60 & 120KHz emanating from the DC-DC switcher in the Biasing Tee.
I've left it connected to one of my KiWi SDR's so that folks can try it for themselves.
You can use my other KiWi with a Loop on the ground as a reference.
Based on my tests, I wouldn't recommend it.
Regards,
Martin - G8JNJ
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Hi All
I was fascinated to follow this thread on reverse engineering the MLA-30, However by coincidence whilst I was reading it a news item appeared on TV, it seems in future, due to new EU rules, all items sold commercially must be REPAIRABLE. Something to do with cutting down on disposable throw away items !
Anyway the repercussions could be interesting for various companys like Wellbrook, ?who do indeed pot all there products, which would class them as non repairable from manufacture.?
I've always seen potting as a dual function....one being to help protect one's intellectual property and of course keeping out the dammed water....
To date I have never managed to keep out the moisture, or stopped water ingress into any of my preamps.
Interesting times Paul G4HDS
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Hi Paul,
I don't think (my opinion) that manufacturers will be forced by legislation to not to apply the potting compound, specially if they argue that it is essential for the environmental protection of certain products.
In order to comply with the "repairable" requirement, maybe is enough to split the antenna in two or three parts (DC bias, amplifier body, aluminium loop).
This legislation is known to some EU countries. Back in 1990 or so I remember a fellow Spanish CB-er who dropped his radio and damaged a front panel potentiometer. Legislation back them oblidged importers/distributors to:
- have a parts catalog to buy parts for a reasonable price, or
- make the requested part available by removing it from a new unit, for a reasonable price.
So my fellow CB-er got his potentiometer, but not without initial resistance (pun intended)
73,
Carlos VK1EA
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On Tuesday, October 1, 2019, PAUL UNWIN < paul@...> wrote: > Hi All > I was fascinated to follow this thread on reverse engineering the MLA-30, However by coincidence whilst I was reading it a news item appeared on TV, it seems in future, due to new EU rules, all items sold commercially must be REPAIRABLE. Something to do with cutting down on disposable throw away items ! > Anyway the repercussions could be interesting for various companys like Wellbrook, ?who do indeed pot all there products, which would class them as non repairable from manufacture.? > I've always seen potting as a dual function....one being to help protect one's intellectual property and of course keeping out the dammed water.... > To date I have never managed to keep out the moisture, or stopped water ingress into any of my preamps. > Interesting times Paul G4HDS > > > > Sent from Samsung tablet > _._,_._,_ > ________________________________ > 开云体育 Links: > > You receive all messages sent to this group. > > View/Reply Online (#12744) | Reply To Group | Mute This Topic | New Topic > > ________________________________ > Please trim replies, do not reply directly to a DIgest. Be kind. > ________________________________ > Your Subscription | Contact Group Owner | Unsubscribe [ carlos.peco@...] > _._,_._,_
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On Tue, Oct 1, 2019 at 09:43 AM, PAUL UNWIN wrote:
To date I have never managed to keep out the moisture, or stopped water ingress into any of my preamps.
I've stopped trying to do that, as condensation is a major problem unless you can maintain the internal temperature above the dew point. Any holes piercing an enclosure on the top or sides will eventually let water in, so I now mount all the connectors and cables on the bottom edge of the housing and leave a small drain hole. In really harsh locations I put a second box over the first box, the outer one acting simply as a weather shield. I've got some pre-amps mounted on top of hill top towers, which are very exposed, and this technique seems to have been more successful than any of my previous attempts at waterproofing. Regards, Martin - G8JNJ
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Hi Carlos
I absolutely agree,? the environmental extremes such products must endure makes potting a must.? Therefore any legislation must allow for this. Perhaps the responsibility for any such simple repair work I.e. replacing a simple semiconductor device failure will fall back on the manufacturer.? In this scenario,? I would imagine a simple one for one replacement would suffice.? (A sort of super warranty )
73 Paul
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Paul and other members of this group.
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Reverse engineering the MLA-30 or any other product could be considered as a theft of Intellectual Property and publishing the circuit diagram without the owners consent a breach of copyright law.
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The situation as I see it; one can spend well over a 1000 hours developing a product, then someone comes along and steals the value your hard work.
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? To quote from your mail “ Anyway the repercussions could be interesting for various company's like Wellbrook,? who do indeed pot all there products, which would class them as non repairable from manufacture.”
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What you are saying is incorrect; Wellbrook loops are repairable by replacing the head amplifier module.
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Most other loop manufacturers offer replacement parts for their products even if the replacement products are potted. Put it another way, it is up to the product designer to decide the repair policy.
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Andrew Ikin
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Wellbrook Commuications
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From:
PAUL UNWIN
Sent: Tuesday, October 1, 2019 9:43 AM
Subject: Re: [loopantennas] MLA-30
?
Hi All
?
I was fascinated to follow this thread on reverse engineering the MLA-30, However by coincidence whilst I was reading it a news item appeared on TV, it seems in future, due to new EU rules, all items sold commercially must be REPAIRABLE. Something to do
with cutting down on disposable throw away items !
?
Anyway the repercussions could be interesting for various companys like Wellbrook,? who do indeed pot all there products, which would class them as non repairable from manufacture.
?
I've always seen potting as a dual function....one being to help protect one's intellectual property and of course keeping out the dammed water....
?
To date I have never managed to keep out the moisture, or stopped water ingress into any of my preamps.
?
Interesting times Paul G4HDS
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?
?
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Hi Martin
? ? ? ? ? ? ? ? ? I suppose for those of us tinkering total waterproofing isn't to much of an issue, I doubt any particular preamp I've built has been outside long enough to rust or rot :)? mind you even after a week or so the condensation you mention is often visible,? ?for Andrew and other manufacturer's it must be a royal pain in the butt.. (I was thinking about Auto electronics as well) I think they pot ECU's as well...
73 Paul
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On Tue, Oct 1, 2019 at 10:40 AM, Andrew Ikin wrote:
Reverse engineering the MLA-30 or any other product could be considered as a theft of Intellectual Property and publishing the circuit diagram without the owners consent a breach of copyright law.
Hi Andrew, I agree, having had several of my designs copied by commercial companies. However the Chinese tend to be the worst offenders, and in this case the design is clearly based on Charles Wenzel's Tuned loop antenna,?although it is a bad implementation and needs improvement.?
However my main reason for doing this is that it's packaged to look like an Bonito Nti Megaloop, and I would suggest that reverse engineering it is in the public interest, so that folks know what they are actually buying and are not being deceived.
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Folks who think they are getting a clone for a fraction of the price need to be better informed and hopefully reverse engineering will encourage the manufacturers to produce an updated design that will work better. Regards, Martin
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That is an interesting thought, I wonder what end results we could get? An improved product?
Paul
On Tue, 1 Oct 2019, 8:03 p.m. Martin via Groups.Io, <martin_ehrenfried= [email protected]> wrote: On Tue, Oct 1, 2019 at 10:40 AM, Andrew Ikin wrote:
Reverse engineering the MLA-30 or any other product could be considered as a theft of Intellectual Property and publishing the circuit diagram without the owners consent a breach of copyright law.
Hi Andrew,
I agree, having had several of my designs copied by commercial companies.
However the Chinese tend to be the worst offenders, and in this case the design is clearly based on Charles Wenzel's Tuned loop antenna,?although it is a bad implementation and needs improvement.?
However my main reason for doing this is that it's packaged to look like an Bonito Nti Megaloop, and I would suggest that reverse engineering it is in the public interest, so that folks know what they are actually buying and are not being deceived.
?
Folks who think they are getting a clone for a fraction of the price need to be better informed and hopefully reverse engineering will encourage the manufacturers to produce an updated design that will work better.
Regards,
Martin
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Matt M0LMK - KI5GXV
Everett N4CY