Among the alternative energy sources, one of the most promising is that represented by Astro-Rei. Readers who want to try this “sun-powered” radio can undoubtedly move on to more advanced energy-saving projects. Of course, this is an experimental radio with only one transistor, which means that if the requirements are small, the audio power achieved and the sensitivity in capturing medium wave stations are also small, so an antenna of at least 10 meters long should be used for local stations, and only in exceptional cases the listening can be done over a loudspeaker. The normal thing is the headset. The coil must be formed by 100 turns of enameled copper wire number 28, in a shape of 2.5 cm in diameter. Regarding the solar battery, we suggest using a 2N3055 transistor with the junction exposed to light (remove the transistor's “helmet” to transform it into a solar battery). The voltage obtained under the indicated conditions is of the order of 0.6V, which means that T1 should, preferably, be a PNP germanium transistor such as 25B75 or OC74. The output transformer must have a primary winding of more than 500 ohms, and it is very important that the grounding is good.
