A monolithic phase locked loop for data communications. The IC contains a basic phase locked loop for tracking an input signal within the pass band, a quadrature phase detector which provided carrier detector and an FSK voltage comparator which provides FSK demodulation.
http://www.next.gr/inside-circuits/FSK-Demodulator-Tone-Decoder-with-RC2211N-l5858.html
For a long time I have thought it would be cool to build some sort of a modem. And finally I had the need for something that could send low-speed wireless data from my GPS to a computer.
http://www.andrewkilpatrick.org/mind/rtty_modulator/
The series output transistor is a VHF power transistor. It has flat response out past 20 MHz, less than 1 percent total harmonic distortion, and does not generate significant levels of IMD. The results show an emission bandwidth greater than 18 MHz at -38dbc levels. use of a Mirage D24 solid state power amplifier after the transceiver served to increase the bandwidth of the transmitted signal even further.
http://www.qsl.net/kd2bd/modulator.html
used for generating a high quality FM stereo multiplex signal that is suitable for driving mono FM transmitters.
http://www.solorb.com/elect/fmst/
http://www.web-ee.com/Schematics/PWM/pwm.htm
http://www.mrs.bt.co.uk/dubus/8402-3.pdf
simple and useful circuit used to monitor on air transmission of your low power amplitude modulated transmitter
http://www.flashwebhost.com/circuit/modulation_monitor.php
-sideband (SSB) modulation uses the frequency spectrum and generates output power more efficiently than does full-amplitude modulatio, generates generates 35- to 80-MHz SSB signals by combining wideband, low-voltage op amps with an IC that integrates all
http://www.edn.com/archives/1997/060597/12di_02.htm
http://www.4qdtec.com/pwmmod.html
http://www.web-ee.com/Schematics/RF_Modulator/rf_modulator.htm