RF

A current-feedback amplifier is a well-known component with many uses. Its basic block diagram shows that its input stage is a voltage follower—in practice, a symmetrical emitter follower (Figure 1). The configuration samples the output current, converts it to voltage across a large impedance, and amplifies it to the output using a high-power, low-output-impedance amplifier.

Figure 1 shows a novel circuit that uses a low-cost, high-speed op amp as a crystal-controlled RF sine-wave oscillator. An op-amp oscillator offers several advantages. Because an op amp is a complete amplifier with a high-impedance input and a low-impedance output, it considerably simplifies the circuit design by replacing the traditional multiple-transistor circuit with its interstage transformer and numerous other components.

This is an image Schematic. No Description available.

This circuit is similar to CMOS INVERTER 125KHz LC OSCILLATOR but adds even more inverters in parallel to deliver yet more power. The values shown are for 125KHz

This circuit is similar to CMOS INVERTERS FORM 125KHZ OSCILLATOR but adds more invertors in parallel to deliver more power. The values shown are for 125KHz.

This circuit is similar to schematic CMOS INVERTER 125KHz LC OSCILLATOR but inverts the LC components so the inductor is grounded. Two inverters are needed to produce the needed oscillation. Again, the values shown set the frequency at 125KHz but can be changed to produce other frequencies.

This circuit uses a single CMOS inverter to form a series resonant LD oscillator. The values shown set the oscillation at about 125KHz buth other frequencies are possible by changing the main LC values.

I have used this parallel resonant LC oscillator circuit countless times. The oscillator frequency is determined by the inductor and capacitor values. I have shown an adjustable inductor to make it easy to set the frequency to a specific value. Once set the frequency is fairly stable over supply voltage variations and temperature changes. The values shown are for 125KHz but the frequency can range from tens of kilohertz to tens of megahertz. With a 74HCU04 type inverter, it will oscillate down to about 1.5 volts.

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.

The circuit is a very simple oscillator that will give an output of up to one watt. The only critical component is the isolating/output coil in the cathode (fillament). This is wound upon a 1/2" dia ferrite ring and consists of 17+17 turns of wire to connect the 1.4 volt fillament supply to the valve fillament. The two enamelled wires must be twisted together before winding. The output from the transmitter is taken from the same coil, by adding another winding of just a few turns. The number of turns will depend upon the valve used, but a good starting point is five turns.

The two tubes form a push-pull power oscillator, which makes alternating current, but at a radio frequency. This is done by the use of L1, L2, L3 and the two little tubes (type 833 - alternatively F-24-a). The actual frequency is not really important, as the object is to generate maximum bandwidth .. the goal of any phone station. C1 is used to obtain maximum power by resonating L1 to L2's natural frequency.

The oscillator can be made crystal controlled; replace the 2p7 with a 5th harmonic crystal. The oscillator will then be very stable, so stable in fact, that it cannot even be modulated! This means that you could only use it to send CW (morse code).