B-field VLF Receiver

Here is a Schematic Diagram of a B-Field receiver I designed in May of 2000. It uses a single turn loop for the antenna, however, it will work with multi-turn loops. The frequency response seems to lower as turns are added to the loop. A single turn of 20 gauge wire 300 feet long works very well. Even a 100 foot loop has a good amount of gain. The main drawback is the sensitivity of this system, you must seek out a site VERY far from AC power, B-field receivers can pick up AC noise several times better than E-field receivers. In some instances, properly positioned, you can orient the antenna for an AC null. Low pass filtering can be added to the circuitry, if an LM324 op amp is used, there are a couple of unused stages that a filter can be built out of. This unit provides a LINE LEVEL output, not Mic level output. For stereo reception of VLF, first, you must build two of these receivers, second, you have to orient the antennas of each unit at 90 degree angles from each other. Each antenna should be the same length and at equal height.

Click here for the schematic diagram

Update: (6/1/00) I have made a few changes to the circuit, added an active low-pass filter section with the unused portion of the LM324 op-amp. Also, I improved the gain somewhat with a lower impedance transformer.

Click here for the updated schematic diagram