Free Circuit Diagram

This radio modem is popular for amateur radio packet application. This radio modem is powered by the data and control lines, so it need no additional power supply. Just plug to your standard RS232 port and this modem will work. As seen in our previous modem circuit, this radio modem circuit also uses TCM3105 modem [...]

ROHM (www.rohm.com) is originally a resistor producer company, but finally expand their business and produce monolithic IC, and this one used in our circuit is the example. The internal structure of this FM transmitter integrated circuit consist of stereo modulator that creates a stereo composite signal, an FM modulator that modulate a carrier frequency with [...]

TDA 1072AT is a special purpose integrated circuit for AM radio receiver from Philips Semiconductors. The integrated circuit is designed for mains-fed home receivers and car radios. The voltage-controlled oscillator provides signals with extremely low distortion and high spectral purity over the whole frequency range even when tuning with variable capacitance diodes. RF radiation and [...]

Notch filter is known as band-cut filter or band-reject filter. The fuction of this filter is to remove some frequency portion of a signal. The schematic diagram of this filter circuit, a second order notch filter is depicted in the figure below. The formula is actually complicated, but by taking the R3=R4 and [...]

A PLL system can be used to implement an FM demodulator. When a PLL is locked on an FM signal, the VCO tracks the instantaneous frequency of that signal. Since the VCO output tracks the FM signal, and the VCO input voltage is proportional to the VCO output frequency, then the VCO input will be [...]

This FM transmitter circuit is small, similar to our previous single chip FM  transmitter, but this FM transmitter is monophonic. You can see in the circuit’s schematic, the left and right signals is mixed before modulate the radio frequency. Here is the schematic diagram of the circuit:   The core of this [...]