1.8MHz AM transmitter and receiver

Before starting on the receiver side of the` Chatterbox`, we ought to take a final look at the transmitter itself. The Chatterbox transmitter is built separately, because many constructors will want to use it in conjunction with an existing receiver on 1. 8MHz. It`s been assumed that an existing antenna tuner and low-pass filter unit will be used w
1.8MHz AM transmitter and receiver - schematic

ith the transmitter. However, if you intend to use the complete transmitter and receiver combination as a `stand alone` unit, it will be necessary to use a suitable low-pass filter to reduce potential harmonics. A filter of this sort can be built into the transmitter, or it can be an outboard type used in conjunction with a small antenna tuner. What the individual constructor does of course, will depend on the size of casing and whether or not the project is built as separates or as one small unit. With the change-over switching described in the previous article, the transmitter can be used with any 1. 8MHz receiver. If you don`t have a suitable set, you can add a simple single board receiver of the sort described here. However, bear in mind that the receiver is not a DX model and it`s designed for using the Chatterbox combination in local a. m. nets. The receiver section is based on the TDA1072A a. m. receiver i. e. This is an inexpensive chip which performs all the functions of an a. m. receiver between the antenna and the audio stages. The TDA1072A`s sensitivity and signal handling capabilities are such that it`s suitable for this application. The i. e. also supports several features not used in this design. Some of the features are made available on the p. c. b. , should you wish to incorporate them in the receiver. For example, the chip provides an S-meter output, a muting facility and a buffered oscillator output for...

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