Radio Frequency - Related Circuits

Radio equipment interfacing

• Connect two standard office telefax machines via 2 meter ham radio (at 2400 bps) - zipped file  

Amplifiers

• 1 Watt C-Class RF Amplifier - auitable for 30 MHz, 100 MHz and 200 MHz  
• 15 Watts RF Amplifier - This circuit will put out a conservatively-rated 15 watts across the FM broadcast band. 
• 300 Watts RF Amplifier - This circuit will put out a conservatively-rated 300 watts across the FM broadcast band.  
• High-frequency AGC has digital control - 50 mHz AGC circuit 
• High-frequency VGA has digital control - variable-gain amplifier for ranging from 115 MHz at high gain to 225 MHz at low gain  
• Wideband AGC has 60-dB dynamic input range - provides more than 60 dB of dynamic input range at 150 MHz  

Modulators

• 602 Double Balanced Mixer - Philips describe their 602 mixer (SA602A) circuit as "a low-power VHF monolithic double-balanced mixer with input amplifier, on-board oscillator, and voltage regulator. It is intended for high performance, low power communication systems. The guaranteed parameters of the SA602A make this device particularly well suited for cellular radio applications. 
• Add-on modulator has high bandwidth - converts the output of a continuous-wave (CW) source to either an amplitude-modulation (AM) or a suppressed-carrier-modulation (SCM) format, circuit has unity gain and 50 Ohm input and output impedances, frequency response is flat from 0.3 to 45 MHz 
• Current amp provides frequency modulation - you can use current-feedback op amps in many VHF-band RF applications up to 150 MHz, this frequency modulator that generates a 55-MHz VHF signal  
• Modulator draws just 5 mA at 2.7V - single-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 the necessary functions  
• Single-sideband demodulator covers the HF band 

Demodulators

• Waveform generator demodulates FM signals - uses the phase-detector signals of a precision waveform-generator IC to perform FM demodulation 

Converters

• 900-MHz down converter consumes little power - nonproprietary 900-MHz down converter to 75 MHz by using an 825-MHz local-oscillator signal 

Oscillators

• Gate Deep Oscillator - This is just a variable oscillator based on a bf245 or k 161 fet. By changing the coil it can generate frequency between 0.5 and 300 MHZ. this circuit is useful to test radio circuit such as filter, receiver, transmitter and so on . It can be use for coil tuning thanks to the 100microamo meter built in. 
• Low-cost circuit biases VCOs for cable and TV - PLLs are useful in a variety of applications, most notably cable and TV tuners  
• Op-amp oscillators simplify RF designs - a novel circuit that uses a low-cost, high-speed op amp as a crystal-controlled RF sine-wave oscillator 

Radio signal detectors

• Cellular Phone Helper - activates a variety of devices when your cellular phone is in use, pdf file  
• RF Sniffer 500 kHz to 500 MHz  

Filters

• Analysis of pairs of Coax Stubs - article about coaxial stubs for filters on transmitters  
• Analysis of Single Coax Stub  
• K2TR Coax Stub Filters  
• W3LPL Receiving Bandpass Filters - information extracted from a July/August 1985 NCJ article  

Other

• FM Pre-Emphasis - FM broadcasting in the United States requires a 75us pre-emphasis for proper frequency response at the receiver. This is a high-precision pre-emphasis module that goes in front of the main broadcast limiter, but after the optional sibilance limiter.  
• Harry's Homebrew Homepage - very many radio related projects 
• Micro Power FM Broadcasting Circuits - limiter, mixer, antenna, modifications to Ramsey FM10 
• Radio and RF circuit at Wenzel Associates technical library