This stereo encoder is a halfway between analogue and digital processing. It combines the best from both domains to provide high-quality and easy to build device. The sampling frequency used in this stereo encoder is 97 times higher than the pilot tone frequency. This makes very easy to reject all spectral residues around the sampling frequency without affecting the main signal characteristics. Using of a microcontroller allows to build this stereo encoder with reduced part count and get excellent results in real operation. This stereo encoder advisedly does not contain any preemphasis circuit. Remember the key fact: a compressor/limiter/clipper device must be always present between the preemphasis circuit and the stereo encoder or modulator. Only this configuration ensures loud sound without exceeding the maximum frequency deviation limit (75 kHz). The stereo encoder is designed to provide really good sound. This always needs to use the compressor/limiter/clipper device where the preemphasis is precisely assured.
Posted on Saturday, February 5, 2011 • Category: FM Radio / Receivers
Traditionally, in a crystal detector radio tuned circuits, a mechanical type variable capacitor is used. For those of you who would like to eliminate this mechanical component, here is a modern version of the classic detector set. This radio, as shown on Figure 1, uses a varactor diode instead of the usual mechanical rotary device. The varactor is also known as a variable capacitance or a varicap diode. It provides an electrically controllable capacitance, which can be used in many different circuits. Varactors are small and inexpensive, which makes their use advantageous in many applications. Its disadvantages are a lower Q (quality), nonlinearity, lower voltage rating and a more limited capacitance range. A tuned circuit with a higher Q has a narrow pass-band that makes it better able to pick out a station of many equally strong. A lower Q tuned circuit has a wider pass band. It allows more neighbor stations through and makes listening to either radio stations frustrating. Frequency change with a varactor diode equipped tuned circuit is as simple as a voltage change.
Posted on Sunday, January 30, 2011 • Category: FM Transmitters
So, I needed a small transmitter, which would allow me to transmit good, old music into my AM-only radios. So, one saturday afternoon I got into gear, designed and built a very crude, terribly non-optimized little transmitter. It's almost a joke expressed in electronics, full of poor design, so please don't think that this is the best I can do! You must see it as a quick and dirty 5-hour effort, because that's all the time the transmitter took to design, build, and test. Making this web page about it is taking much longer! I'm putting this thing on the web only because many people have asked me to do so, despite its crude design!
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