Using digital techniques has caused a resurgence of interest in VLF — very low frequency — radio. Thanks to software-defined radio, you no longer need huge coils. However, you still need a suitable ...

When you think of directional ham radio antennas, you probably think of a Yagi, cubical quad, or a log-periodic antenna. These antennas usually are in a horizontal configuration up on a high tower.

The author is a consultant in Carterton, New Zealand. This follows up his December article “Tuned Bandpass Filter Is Solution to Backup STL.” Many years ago, the active whip antenna and the active ...