Loudspeaking crystal radio receivers

Posted on Feb 7, 2014

A lots of radio amateurs have an interest to power a simplest radio receivers with the `free energy`, i. e. the energy, taken by the receiver antenna directly from the air. The circuits described here can provide a radio reception using a loudspeaker. The question of how much power can get out of a signal from an antenna, and how to build a loudspe

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aking crystal set, was already discussed in the author`s articles [1, 2]. However the questions "how much power we need for loudspeaking reception " and "how to better use the power from the antenna ", still remain. According to the old reference books, to listening a voice of a broadcaster from the distance of 1 meter it takes the sound level of the loudspeaker about 60 dB. In this case, the radiated acoustic power is 12. 6 W. The necessary electrical power can be calculated by dividing the radiated acoustic power by the energy conversion efficiency of the loudspeaker. For the common loudspeakers the energy conversion efficiency is about 1%. Thus we get the electrical power about 1mW. It is interesting to calculate the required power for loudspeakers to get the sound level of 60 dB. The calculation results for the different loudspeakers are presented in table 1. From the table 1 we see that we need to use the high-efficiency loudspeakers. The acoustic design of the loudspeaker systems is very important, the bigger speaker cabinets is better. In the experiments the author used two loudspeakers type 4GT-2 in wooden cabinets with the enclosure volume of 50 liters. Horn loudspeakers has three times better efficiency because of the improved coupling efficiency between the speaker driver and the air and because of the directional characteristics of the produced sound waves. The simple and effective loudspeakers was built by...

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