Inside the MLA-30 Active Loop Antenna

You’ve probably seen the MLA-30 Active Loop Antenna on Ebay. It can be had for a bargain price of around £35 and works great for the price. There’s only one problem in my book; the PCB is covered in epoxy potting and you can’t see the design or repair/modify it! Something that I’ll have to fix!

What follows is the results of 45 minutes in the kitchen with a pan of boiling water and a pair of tweezers. Behold, the MLA-30 in all its naked glory!

A single screw hidden beneath the epoxy holds the PCB into the case.

The PCB removed.

Underside of the PCB.

Boiling the PCB to remove the epoxy. Note to self: Don’t use the wifes best pan!

Slowly removing the epoxy. Once it reaches it’s plasticizing temperature, it just peels off like putty.

Not bad. Only 2 small inductors were damaged. I’ll replace these and see if the PCB still works once I’m done drawing the schematic.

And now, the moment we’ve all been waiting for. The naked MLA-30 PCB!

So, it looks like a single chip amplifier design and it’s pretty obvious to see that the Pot is a simple gain control. I hope that answers some questions about this interesting little loop.

8 Replies to “Inside the MLA-30 Active Loop Antenna”

  1. Excellent post! I’ll be interested to see that schematic when you’re done. Nice work!

  2. Thanks for the dissection and your efforts in helping out. If possible, please email me when you have your schematic done.

  3. Due to the Layout of the PCB and the Pinout of the OPAMP i guess that a differential Input OpAmp/Line Driver like an LMH6550 is used. It would perfectly fit to the Purpose and ists Pinout fits to the rest of the components.

  4. From what I’ve seen so far, you could be bang on the money there Fred. Nice work!

  5. HI All,

    Matt has kindly sent me the PCB to play with.

    The IC is not a LMH6550.

    It’s some sort of fully differential amplifier with a resistor controlled gain adjustment .

    SOIC-8 package
    Inputs on pins 1 & 8
    Outputs on pins 4 & 5
    Gain control on pin 7

    Any suggestions as to type ?

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