Portable AM Receiver Using ZN414 Integrated Circuit

Figure 1 

The circuit exemplifies the use of ZN414 IC to produce a handy AM radio receiver.

• ZN414 IC– a composition of transistor tuned radio frequency (TRF) circuit packaged in a 3-pin TO-92 plastic package for simplicity and space economy; has low current consumption, easy to assemble without alignment, simple and effective AGC action, excellent audio quality and minimum external components required.
• Amplitude Modulation – a method of emphasizing data on an alternating current waveform or radio wave wherein the carried transmitted signal varies with reference to the amplitude; the highest frequency of the modulating data is typically less than 10 percent of the carrier frequency and the overall power signal varies depending on the amplitude of the modulating data
• Op-Amp – a DC coupled high gain electronic voltage amplifier with differential inputs and usually a single output.

In this design, the circuit will operate on a range of 550 to 1600 KHz medium wave frequency band. The circuit utilizes the ZN414 IC that incorporates several RF stages, automatic gain control and an AM detector although it is very vital to achieve good results of the functioning voltage because the IC gets easily overloaded. The voltage regulator utilizes BC108B transistor which is particularly suitable for use in AF input and driver stages wherein the collector is electrically connected to the case. Along with the IC are four diodes for high speed switching, two preset resistors and a series resistor. The operating voltage for ZN414 is being controlled by the potentiometer as well as acting as the selectivity control for the whole receiver. The voltage can be decreased if the receiver is in the area with resilient radio signal.

An inverting 741 op-amp is used by the audio amplifier because of its low noise feature as it replaces the old style op-amps. The use of BC179 transistor, which has the same feature as BC109, was for the purpose of propelling the loudspeaker and providing more current to the circuit. With the voltage gain around 15, a good quality and distortion free output can be obtained from the entire receiver circuit.

Aside from being utilized as domestic portable receiver, the ZN414 IC can drive a sensitive earpiece directly, can be used in model control receiver as an I.F. amplifiers, as broadcast band superhet.

Source:www.zen22142.zen.co.uk/Circuits/rf/ZN414.htm