So, great news. I have taken the original LZ1AQ loop amplifier project, fabricated a custom PCB and built it with surface mount parts. It works great.
Back in 2011, LZ1AQ published a simplified wideband magnetic loop amplifier design. Recently, I implemented this circuit on a breadboard and was pleased with the performance. As a result, I decided to make the real thing on a PCB.
Using KiCAD, I created a custom printed circuit board and sent it off to OSH Park for fabrication. As shown above, my board is about 1.5 by 2.5 inches. I ordered the parts from Mouser and, when they arrived this week, assembled a finished circuit. All good. The PCB version has slightly higher gain than the breadboard.
My total parts cost for this amplifier was around US $12. Half of that was the PCB.
If you are interested in duplicating this LZ1AQ loop amplifier project, I am sharing my PCB design through OSH Park. The total cost of three boards is US $17.50. You will find the assembly and bill of materials covered in a future article. But, if you can’t wait, you can download the complete project documentation.
LZ1AQ Loop Amplifier Project – Performance
This wideband loop amplifier performs well, pretty much as modeled in LTSpice. You can see modeled loop output when my 1 meter loop is fed with a 50 μV or S9 signal. According to the simulation, 3dB bandwidth is 200 kHz to 10 MHz.
Yes, this is a bit disappointing at the high end, but still usable up to around 20 MHz. The 6dB bandwidth is 180 kHz to 18 MHz. Above that, gain drops off fast. But the good news is that you won’t need to worry about bleed through from strong local FM stations. And besides, it is going to be a few years before there is much to hear at upper HF.
Performance on long and medium waves is great. If you just want to use a 1 meter loop on lower ham bands, though, you might want to incorporate a high pass filter at the front end.