LF/MF ACTIVE ANTENNAS
Active antennas have become very popular for amateur radio LF and MF reception. A typical antenna (such as a diplole or vertical) are much too large for the typical suburban lot. Active antennas typically include the antenna itself, followed by a preamp or impedance matching circuit. Some active antennas are magnetic loops, while other designs are commonly called “E-field probes”.
During AMRAD’s previous LF experimentation, Frank Gentges (K0BRA) and… designed an E-field probe, which was highlighted in QST. Here is his original article:actant.pdf. Some additional information/FAQ on this antenna can be found here: activeantfaq.
There are several other active antenna designs for LF and MF operations. One of the most popular is the PA0RDT design, with more info at DL1DBC, which is fairly simple to build. It uses a small section of PC board, with an optional whip antenna, as the antenna element, followed by a two-transistor amplifier/impedance matching circuit. Futher information regarding the PA0RDT (and how Active antennas work) is on the DL1DBC.net site. A kit version, as well as bare circuit boards, of the PA0RDT antenna is often available on ebay for under $20. Search for “Mini-Whip active antenna”, the kit is sold by chuckwa3iac. Built versions are also available on ebay.
Another, more expensive option for an active antenna that works well is the Z1501D, by Clifton Labatories. It is available in kit form, including the Z1203B power coupler, at about $230, or assembled for about $310.
There are many more active antenna designs for LF/MF operations, they will be added as AMRAD and LCCC members evaluate them.