Volt controlled

The VFC (voltage-to-frequency-converter) circuit in Figure 1 achieves a wider dynamic range and a higher full-scale output frequency—100 MHz with 10% overrange to 110 MHz—by a factor of 10 over any commercially available converter.

If you need a clean emitter coupled logic (ECL) type signal between 200MHz and 400MHz this circuit works fine. It uses four voltage-controlled capacitors to change the frequency.

Here is the latest and greatly improved TX200 VFO/VCO FM transmitter. The most versatile transmitter to date that can be turned into high fidelity stereo PLL based 200mW FM transmitter. It is a perfect circuit for transmitting your music around the house and yard. TX200 uses only two coils; one in the oscillator and the other one in the 200mW VHF amplifier so it should be fairly easy for anyone to build. It also includes built-in pre-emphasis and C5 for enhanced sound quality. While assembling the transmitter care must be taken to make sure that C1 is directly connected to L1 and C9 to L2. These caps eliminate the distortions form the DC supply and improve the sound quality greatly. 9V voltage supply is also very important because it provides the exact amount of current to Q1 to produce loud and clear sound quality.

This circuit was designed to frequency modulate a 40KHz carrier, using human voice frequencies. A common flip/flop is used at the core of the circuit.

The circuit in Figure 1 uses a Microchip 8-pin µC (PIC12C671) as a voltage-controlled oscillator (VCO). Because the PIC12C671 has an internal 4-MHz oscillator, four-channel 8-bit A/D converters, and built-in power-reset circuitry, you need no external components to configure the VCO. The µC reads two analog inputs through AN0 and AN1. The reference voltage for the A/D conversion is the µC's power supply VDD. The converted 8-bit data determines the duration of output high and output low. Assume, for example, the digitized outputs from AN0 and AN1 are 43 and 87, respectively. Timer 0 loads the 43 after the µC sets output GP2 to logic one. Timer 0 receives its timing from the internal clock.

The circuit in Figure 1 uses a Microchip 8-pin µC (PIC12C671) as a voltage-controlled oscillator (VCO). Because the PIC12C671 has an internal 4-MHz oscillator, four-channel 8-bit A/D converters, and built-in power-reset circuitry, you need no external components to configure the VCO. The µC reads two analog inputs through AN0 and AN1. The reference voltage for the A/D conversion is the µC's power supply VDD. The converted 8-bit data determines the duration of output high and output low.

The circuit in Figure 1 uses a Microchip 8-pin µC (PIC12C671) as a voltage-controlled oscillator (VCO). Because the PIC12C671 has an internal 4-MHz oscillator, four-channel 8-bit A/D converters, and built-in power-reset circuitry, you need no external components to configure the VCO. The µC reads two analog inputs through AN0 and AN1. The reference voltage for the A/D conversion is the µC's power supply VDD.

Modern set-top DBS TV tuners require high performance, broadband voltage control oscillator (VCO) designs at a competitive cost.To meet these goals, design engineers are challenged to create high performance, low-cost VCOs.

The heart of the synthesizer is a set of 2 Analog Devices AD9850 direct digital synthesis (DDS) chips. These provide 2 channels of sinewave output which may differ in frequency and relative phase. The output stage of the synthesizer also includes separate variable attenuators for the 2 channels. These attenuators have a range of 0.0 - 63.9 dB of attenuation, in 0.1 dB steps. The user therefore has control over five parameters: 2 output frequencies, 2 output attenuations, and relative phase between the 2 channels.

The aircraft communication in Sweden is still Amplitud Modulated (AM). The local airport (Axamo) use the frequency 118.250 MHz. The reveiver I will explain is a tunable AM-receiver for this frequency. The receiver is instead manually tunable with some 100kHz around the 118MHz. The output from the receiver is a low level output (100-200mV) so you must connect it to some kind of amplifier. I will not explain how to build an audio-amplifier. The hart of the receiver is the Voltage Controlled Oscillator (VCO).