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Fix formatting issues in README.MD file.
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dilshan committed Oct 5, 2021
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Expand Up @@ -11,9 +11,11 @@ In this new design, we divide this receiver into several blocks, which include,
In this prototype build, the *Si5351* clock generator drives using an *Arduino Uno* board. With the given sketch, the user can tune and switch the shortwave meter bands using a rotary encoder. The supplied sketch support clock generation from 5205kHz (tuner frequency : 4750kHz) to 16285kHz (tuner frequency : 15830kHz). If required, this range can further extend or reduce by modifying the Arduino source code. In the given source code, we use [*Etherkit's Si5351 library*](https://github.com/etherkit/Si5351Arduino) to control the clock generator module.

![Prototype version of the filter, mixer and detector PCB.](https://raw.githubusercontent.com/dilshan/arduino-superhet/main/resources/arduino-superhet-mixer.jpg)

This receiver uses a conventional 455kHz I.F transformer kit in an intermediate frequency amplifier. We use a [2SC724](https://www.web-bcs.com/transistor/tc/2sc/2SC724.php) transistor for each filter stage. The value of this transistor is not critical and can be replaced with any suitable mid-frequency NPN transistor, for example, [2SC930](https://s.click.aliexpress.com/e/_9vi1D5), [BF494](https://s.click.aliexpress.com/e/_Ap8gur), [BC337](https://s.click.aliexpress.com/e/_9gRclD), or [2SC829](https://s.click.aliexpress.com/e/_ACedU7), etc.

![Prototype version of I.F amplifier.](https://raw.githubusercontent.com/dilshan/arduino-superhet/main/resources/arduino-superhet-if-amp.jpg)

The 2nd PCB consists of a filter, mixer, and detector circuit. This mixer stage also uses the NPN low power transistor and can replace with any of the above transistors. The crucial component of the detector phase is the [OA90](https://s.click.aliexpress.com/e/_AknfCT) or [1N34](https://s.click.aliexpress.com/e/_AdOUUn) Germanium diode. It can also change with any suitable Germanium signal diode.

The front filter stage constructs using a pair of readymade [1µH inductors](https://s.click.aliexpress.com/e/_ApVWb9). The suggested supply voltage to this tuner is 6V to 9V.
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