VLF Loop Antenna Amplifier

Chris Moulding

Following some recent discussions on this and other forums I've spent some time looking at the original design of the Loop Antenna Amplifier.

The original design used a DC coupled amplifier with a very low input impedance to match small loops (around 1m diameter) efficiently at low RF frequencies. However many customers wanted better HF performance at the expense of VLF and LF so the amplifier was re-designed.

I've decided to look again at the original design as a pure ELF/VLF/LF antenna and design the low pass filtering in the amplifier so that it cuts off above 1.6 MHz to remove HF and local VDSL interference.

The combined frequency range of the VLF head unit and the bias tee board is 500 Hz to 1.6 MHz. This makes it ideal for ELF and VLF research, NDB beacons and long wave and medium wave DXing. Initial testing with a 1m diameter coax loop at 4m above ground gave some spectacular signal to noise results on VLF, long wave and medium wave stations.

Following testing I've built a small batch of VLF Loop Antenna Amplifiers and information on them has been added to the Loop Antenna Amplifier web page:




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