Local Oscillator Pdf
Articles needing additional references from November All articles needing additional references. This is known as cathode injection, and helps to isolate the local oscillator from the other parts of the mixer. In my receiver, the range turned out to be kHz, rather than kHz.
Greg Latta at glatta frostburg. The low-impedance output of the emitter follower matches the impedance of the cable. The mixer stage is used to increase the received frequency to an intermediate frequency. Electronic oscillators Radio electronics Feedback.
The two sections are internally shielded from each other. The local oscillator is, therefore, essential to efficient operation and must be both tunable and very stable. The plate resistor drops the voltage slightly, but its main purpose is to keep the plate isolated from other circuits connected to the regulated power supply.
The oscillator must produce enough output power to effectively drive subsequent stages of circuitry, such as mixers or frequency multipliers. From Wikipedia, the free encyclopedia. Please help improve this article by adding citations to reliable sources.
This is known as image-frequency interference. The output stage of the receiver is normally an emitter follower. There aren't any components which can distinguish a negative frequency of a positive frequency.
The exiting frequency is either higher or lower than the incoming frequency. This transformation is made by a super heterodyne receiver. These frequencies are applied to the mixer stage.
With my receiver, the local oscillator wound up covering covering a range of kHz, somewhat more than originally intended. The local oscillator must produce a stable frequency with low harmonics. The local oscillator is operated from a regulated voltage source to eliminate changes caused by a fluctuations in the supply voltage. Connections must be short, tight, what is inequality pdf and stiff to prevent microphonics. The borders of the bandwidth of this amplifier are choosen to eleminate the image frequencies.
When combined with the bandset capacitors in the local oscillator tank circuit, the main tuning capacitor will cover a range of approximately kHz. The local oscillator is the heart of the receiver. The greatly simplifies construction and results in higher performance. Because of this, the local oscillator must be built with the greatest care and the best components available. Changes in the plate voltage will alter the frequency of the local oscillator, so the plate voltage is obtained from a regulated souce.
It is possible for these receivers to receive two different stations at the same point of the dial. The video amplifier receives pulses from the detector and amplifies these pulses for application to the indicating device. The video pulses are coupled through the cable to the indicator for video display on the crt. This is equal to the bandwidth of most receivers and would greatly decrease receiver gain.
The Figure shows a block diagram of a typical superheterodyne receiver. This article needs additional citations for verification. This method of obtaining bias for the tube is known as grid leak bias. This has any disadvantages.
The mixer also receives an input from the local oscillator. Plate voltage has a large effect on the operation of the local oscillator, so it is obtained from a V regulated supply.
The actual range covered depends on the bandset capacitors and the main tuning coil. The output of the filter are only the frequencies of the desired frequency-band. However, a video amplifier must be capable of a relatively wide Frequency response.
This is exactly the same method that used in a typical regenerative receiver. The triode is used as the local oscillator, and the pentode is used as the mixer. This filter must filter the desired intermediate frequency out from the mixture frequencies arisen in the mixer stage. This is very much like pushing on a swing to keep it moving.
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