Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.
The maximum frequency of the 74ls124 VCO is about 30MHz. So if you need a transmitter in the FM broadcast band, you need a bandpass filter tuned to a VCO harmonic.
As an RC oscillator, 74ls124 is not very stable and may be very noisy to use as an FM modulator. The control and power voltage should be very well filtered, else the power supply noise and ac hum will modulate the tranmitter.
The VCO frequency deviation is about 5MHz/volt and on the 3rd harmonic is multiplied to 15MHz/V. Wideband FM uses 75kHz deviation, so the peak modulation voltage would be 75k/5M = 15mV!!!!!!!!
Use an LC oscillator, is more stable and clean. I think 74LS124 cant be used here.
This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
By continuing to use this site, you are consenting to our use of cookies.