AM portable radio receiver by ZN414 IC

AM portable radio receiver by ZN414 IC

Description:


An AM portable radio receiver made from the ZN414 IC. The ZN414 ic has now been replaced by the MK484 which is identical in performance and pinout.



Notes:

Designed around the popular ZN414 IC this receiver covers the medium wave band band from approximately 550 to 1600 KHz with the values shown. The coil and tuning capacitor may be taken from an old MW radio to save time. The ZN414 IC, has now been replaced by the MK484. The integrated circuit is a 3 pin, tuned radio frequency circuit, and incorporates several RF stages, automatic gain control and an AM detector. It is easily overloaded and the operating voltage of th IC is somewhat critical to achieve good results.



In this circuit a small voltage regulator is built around the BC108B transistor, four 1N4148 diodes, the 2k7 and 10k preset resistor and the 820R resistor. The 10k pot acts as a selectivity control for the whole receiver, controlling the operating voltage for the ZN414 (or MK484). If you live in an area that is permeated with strong radio signals, then the voltage may need to be decreased. I found optimum performance with a supply of around 1.2 volts.



The audio amplifier is built about an inverting 741 op-amp amplifying circuit. Extra current boost is provided using the BC109C / BC179 complementary transistor pair to drive an 8 ohm loudspeaker. The voltage gain of the complete audio amplifier is around 15. The audio output of the complete receiver is really quite good and free from distortion. I may provide a sound sample later. Click here to see a picture of my prototype. I used a small wooden enclosure and the complete tuning assembly from an old radio.

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mk484 radio

mk484 radio
rf circuit

A simple MK 484 IC tuned rf (trf) radio

In 1970 Ferranti started the development of a single-chip AM tuner, and by 1973 it became widely available for use. The 414 is no longer in production, but a follow on IC, the MK484 recently became available, and incorporates essentially the same features. It is a 3 terminal device which packs ten transistors providing 3 stages of rf amplification with an input impedance of about 4 Megohms, and giving 72 dB of gain with about 30 millivolts of audio output (rms). Thanks to the editors of Practical Wireless a ham magazine in the UK, and Dr. Philip Miller Tate of Kingston University, who has probably built a dozen or so of these in one guise or another, and sent me one fully assembled, here is one adaptation of this versatile little chip which gives you a nice little portable radio which is stable and virtually idiot proof to build, needs only a 1.5 v battery, and requires a tiny thimble full of parts to give you near-superhet performance. Here is the schematic of the circuit that PW came up with:


more info
or
here

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