MK484 One Chip Radio
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The ZN414 is dead - long live the MK484!
The MK484 chip incorporates RF amplification, AM demodulation, AF amplification and automatic gain control (AGC).
The chip data sheet assumes you will use a 1.5 volt cell to power the radio.
This diagram also includes regeneration (not documented in the data sheet). This is positive feedback of the MK484 RF output back to the input. This compensates for energy losses in the ferrite and the tuned circuit. The feedback consists of a longish wire routed near the ferrite rod. (It is a coil with one turn.) The positioning of this wire is critical. If the coil is in the wrong orientation, the feedback will be negative. If there is too much feedback the receiver will become unstable.
The effect of regeneration is to ...
We have replaced a ZN414 with an MK484 on one of our AlphaKit radio modules. It seems to work at least as well as the original. The pinout is different and the MK484 has to be soldered in, apparently the wrong way round. No other components were altered.
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