We seek to understand and document all radio transmissions, legal and otherwise, as part of the radio listening hobby. We do not encourage any radio operations contrary to regulations. Always consult with the appropriate authorities if you have questions concerning what is permissable in your locale.

Author Topic: MLA-30 Loop antenna  (Read 14927 times)

Offline ~SIGINT~

  • DX Legend
  • ******
  • Posts: 2460
  • N.E. Canada (FN08)
  • .ılılı..ılılı..ılılı..ılılı..ılılı..ılılı.
    • View Profile
    • Milspec Communication Canada
Re: MLA-30 Loop antenna
« Reply #75 on: January 04, 2023, 1442 UTC »
Quote
today the average home is a cesspool of RFI/QRM generators

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

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

Here is what a kit looks like (and the industry acronym for it is a "fox and hound":
Progressive 200EP Inductive Amplifier 77HP

Offline Ray Lalleu

  • Marconi Class DXer
  • ********
  • Posts: 29545
  • Western part of France
    • View Profile
Re: MLA-30 Loop antenna
« Reply #76 on: January 04, 2023, 1521 UTC »
Quote
today the average home is a cesspool of RFI/QRM generators

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

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

Here is what a kit looks like (and the industry acronym for it is a "fox and hound":
Progressive 200EP Inductive Amplifier 77HP

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

I'm just using an old small Sony radio !

D/E/F/G/It/Sp : Dutch/English/French/German/Italian/Spanish
+/- : about 0.02 offset, ++/-- 0.03/0.04 offset
Balanced wire antennas, wire lines and ATU

Offline ~SIGINT~

  • DX Legend
  • ******
  • Posts: 2460
  • N.E. Canada (FN08)
  • .ılılı..ılılı..ılılı..ılılı..ılılı..ılılı.
    • View Profile
    • Milspec Communication Canada
Re: MLA-30 Loop antenna
« Reply #77 on: January 04, 2023, 1616 UTC »
Quote
That site does not specify to what frequencies that tester is sensible.

It is only as good as the speaker that is in the unit and your hearing --- audio frequency range. The key is if it is leaking out of the cable or device, it is leaking into the antenna. I also use my HP/Agilent spectrum analyzer or ICOM IC-705 with a magnetic sensing loop but not everyone can afford that. You can easily find dirty wall warts, LED / fluorescent lights etc ... with the inductive amplifier probe. A used one will only set you back about $20.00. Have to start somewhere.

Offline RobRich

  • DX Legend
  • ******
  • Posts: 1222
  • Tampa, FL USA
    • View Profile
Re: MLA-30 Loop antenna
« Reply #78 on: January 04, 2023, 2145 UTC »
The tinySA is neat gadget for those wanting a basic SA but not needing a lab-grade spectrum analyzer.

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

I have the original model, though there are now models with larger screens, higher frequencies, and whatever other options.... for more money, of course. ;)
Tampa, FL USA | US Map Grid EL88
Airspy HF+ Discovery | Kenwood R-600 + R-2000 | 2x RTL-SDR V3 + NE602 | Si-Tex 200 | Soft66LC4 | Yaesu FRG-7
31' Vertical | 18' End-Fed Vertical | PA0NHC MiniWhip

Offline Teotwaki

  • DXing Phenomena
  • *******
  • Posts: 2971
  • California
    • View Profile
    • My adventures are at Sun To The North
Re: MLA-30 Loop antenna
« Reply #79 on: January 10, 2023, 1916 UTC »
I bought a Chinese MLA-30+ and modified it a little. I desoldered most of the DC-DC converter in the bias T and ran in a line from a 12.6vdc linear supply. I tossed the thin stainless steel loop wire too. I took some aluminum jacketed 1/2" coax and made a loop. I squashed the jacket flat on each end, bent a 90 degree tab and drilled it. It seems to be about 2.9 uH

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

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



The DW beacon
Jim
NRD-525, Elecraft KX3 and Elecraft PX3 Spectrum Display
76' end fed long wire & 66' off-center fed dipole for 10/20/40 meters
Orange County, SoCal, The better half

Offline Pigmeat

  • Marconi Class DXer
  • ********
  • Posts: 6005
    • View Profile
Re: MLA-30 Loop antenna
« Reply #80 on: January 13, 2023, 0253 UTC »
I've built a number of passive loops over the years, starting w/ a MW loop from a schematic from Radio Nederlands. I screwed that one up royally, but it worked on 90 and 40/41 meters with the Walkman tuning cap I used with it. I was able to dx Papua New Guinea, something I wasn't able to do with my wire antenna's and get rough headings on my fellow pirates and found most of them were full of crap about where they were tx'ing from. So was I, so there were no hard feelings, just laughs.

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

I've never tried the MLA-30, but I have listened to online SDR's using it. They seem to work well and are quiet, but I don't know if the owners have modified them? Most radio heads like to tweak their antenna's, and I suspect many of MLA-30's I've encountered have been tweaked. I know for a fact one of them has, as the owner is an old friend. It was sounding good earlier tonight. Have fun playing with them.

Offline RobRich

  • DX Legend
  • ******
  • Posts: 1222
  • Tampa, FL USA
    • View Profile
Re: MLA-30 Loop antenna
« Reply #81 on: January 14, 2023, 2238 UTC »
From one of my posts in the MW thread....

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

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

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

Dropping voltage might improve SNR with the inexpensive video preamp IC used in the MLA-30 design. I assume the MLA-30+ uses the same or similar chip.
Tampa, FL USA | US Map Grid EL88
Airspy HF+ Discovery | Kenwood R-600 + R-2000 | 2x RTL-SDR V3 + NE602 | Si-Tex 200 | Soft66LC4 | Yaesu FRG-7
31' Vertical | 18' End-Fed Vertical | PA0NHC MiniWhip

Offline alpard

  • Full Member
  • ***
  • Posts: 225
    • View Profile
Re: MLA-30 Loop antenna
« Reply #82 on: January 17, 2023, 1410 UTC »
I sold all my radio stuff to buy electric guitars and amp, and have been away from radio hobby for couple of years.  I am recently back to the radio.
From my memory MLA-30+ was OK, but for serious DX stuff, it lacked a bit.  On LW it was non working but from MW to SW, it was OK.
DXing for the low power AM stations at nights, the Wellbrook ML was far better.  But Wellbrook was about 10 times more expensive.
XHDATA D-808, MSi001 SDR, YouLoop, Active MiniWhip

https://www.youtube.com/channel/UCd7MwNa5dATlIXvg1K3eN6A

Offline Teotwaki

  • DXing Phenomena
  • *******
  • Posts: 2971
  • California
    • View Profile
    • My adventures are at Sun To The North
Re: MLA-30 Loop antenna
« Reply #83 on: January 18, 2023, 1712 UTC »
From one of my posts in the MW thread....

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

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

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

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

Rob

Thanks for bringing up the suggestion for the lower supply voltage.

The reverse engineered schematics do not show any on board voltage regulator so I agree that  a +12v supply is too high, assuming the Chinese used a chip specified the same as the TL592B.  I've dropped the voltage into the bias Tee to +6vdc and the loop's amplifier gain seems the same. I'll try to make some signal strength measurements later this week.

Jim

Jim
NRD-525, Elecraft KX3 and Elecraft PX3 Spectrum Display
76' end fed long wire & 66' off-center fed dipole for 10/20/40 meters
Orange County, SoCal, The better half

Offline Teotwaki

  • DXing Phenomena
  • *******
  • Posts: 2971
  • California
    • View Profile
    • My adventures are at Sun To The North
Re: MLA-30 Loop antenna
« Reply #84 on: January 18, 2023, 1740 UTC »
Here is a schematic of the AL1530 Wellbrook loop


The writeup is very interesting too.
https://www.george-smart.co.uk/projects/wellgood-loop/wellgood-loop-history/
« Last Edit: January 18, 2023, 1745 UTC by Teotwaki »
Jim
NRD-525, Elecraft KX3 and Elecraft PX3 Spectrum Display
76' end fed long wire & 66' off-center fed dipole for 10/20/40 meters
Orange County, SoCal, The better half

 


Item image   NAIS AQW225N Solid State Relay 8 Pin DIP MOSFET Output Flat Shipping Any Qty!

 $2.99