The cookie is set by GDPR cookie consent to record the user consent for the cookies in the category "Functional". The cookie is used to store the user consent for the cookies in the category "Analytics". This cookie is set by GDPR Cookie Consent plugin. These cookies ensure basic functionalities and security features of the website, anonymously. Necessary cookies are absolutely essential for the website to function properly. A super-het radio runs 5 years on a C-cell, plus a pentode radio.Low-power, super-regenerative receiver targets 433-MHz ISM band.These extra programs and the stereo pilot do not interfere with the main analog signal as received on the FM tuner described here. The station has two digital auxiliary channels: jazz/classical, and the main channel in HD, all on the same frequency of 90.7 MHz. I listen to an NPR FM station that is mostly talk. This amplifier with a gain of ten will boost the output to audio line level. Another solution is to use the circuit: Build an op amp with three discrete transistors in the Design Ideas section of the Dec. A musical instrument amplifier would work fine due to the high gain guitar input. The output level of the tuner is below line level, so an amplifier with a microphone input would be useful. The tuner needs an audio power amplifier. The 0.04 to 6 pF capacitor is used to tune in stations. A one meter long wire antenna is sufficient. The coil is tapped one half turn from the 12 volt supply side to make a connection for the antenna. When formed, the coil can be removed from the form. The windings are spaced one wire-width apart, so you can close-wind two windings on the form and then remove one of them. The antenna coil is composed of five turns of space wound AWG 18 wire on a 1/4″ form. The quench frequency of this oscillator is about 21 kHz. The adjustment of the quench-level control is critical, so a good single-turn potentiometer should be used in this position. This makes a three-transistor circuit – still quite simple for an FM radio ( Figure 2 ). A two-transistor astable multivibrator is used for this quenching oscillator. Also, the quench frequency may vary with tuning and it may be too high or too low.Īdding an external oscillator to force the quenching of the circuit solves these problems. In the self-quenched circuit, the output may be distorted. It may be necessary to select transistors for the highest gain and to select the operating voltage for best performance. It can be difficult to get the circuit to quench and therefore to operate. The circuit in Figure 1 is a self-quenched circuit. The integrator changes this pulse-width modulation to an audio output. The output to the RC integrator circuit is a series of pulses at the quench frequency that are pulse-width-modulated. High quench frequencies reduce the sensitivity of the receiver. This frequency should be above the limit of human hearing, but otherwise as low as possible. The rate that the oscillation is switched off and on is called the quench frequency. The super-regenerative tuner is a regenerative circuit that is brought into and out of oscillation at a ultrasonic rate – for instance, 25 kHz.
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