Low Frequency Antennas

  
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Home-made antennas can greatly improve the performance of AM and FM radios, short-wave receivers, and scanners. If you are a talk-radio fan then experiment with the AM band antennas and you will be able to hear shows from all over the country with surprising clarity. Short-wave receivers are always coping with weak signals and they must have a good antenna to perform adequately.
Low Frequency Antennas - schematic

Scanners can pick up local police and two-way radio with the little telescoping antenna provided but with good antennas a scanner becomes an amazing ear on the world nearby. No pre-amp, filter or other receiver refinement offers anywhere near the level of performance improvement t that a well-designed antenna offers. The results can be quite satisfying, leaving no doubt that the project was well worth the effort. In the past, designs that incorporated an amplifier in the antenna were called "antennafiers" so perhaps this is a "loopifier". The differential amplifier solves matching issues and the varactor tuning gives excellent out-of-band rejection for even cheap receivers. I think the good common-mode rejection from the differential amplifier eliminates the need for a shield, too. This active antenna for the shortwave band provides surprising performance, even indoors. As the name implies, the main loop is made from a Hula-Hoop with the metallic paint stripped off and a single turn of 14AWG copper wire inserted inside the hoop. (There isn`t any need to remove the paint; mine was flaking and I didn`t like the looks. Half way through I regretted my decision!) These hoops are basically thin-walled plumbing tubing with a water-tight connector holding the ends together. (Mine was actually filled with water to make a "swish-swish" sound, supposedly. ) The ends of the hoop pass through two holes in a plastic project box and are...



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