The receiver is built on a single-sided printed circuit board which measures 2 by 4. 3 inches. The small size means that the board can be fitted into a wide variety of enclosures, which should be well screened. The main directional signal is picked up by a tuned ferrite rod (or loop) aerial and fed, via the R. F. attenuator (RV1) to a low-noise FET
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R. F. amplifier (TR2). A second FET R. F. stage (TR1) amplifies the signal from a vertical whip aerial and can be switched into circuit to give a heart-shape response so that the direction of received signal can be determined. This direction is not accurate, but serves to eliminate one of the two sharp null directions that the ferrite aerial provides. The amplified signal is tuned in a Hi-Q coil (L1) and fed into the TCA440 receiver integrated circuit. This I/C includes R. F. amplifier, balanced mixer, separate local oscillator, I. F. amplifier and voltage stabilizer. The local oscillator is tuned by L2 with VC3 and covers 2. 265 to 2. 455 MHz which converts the incoming signals of 1. 81 to 2. 00 MHz to a 455 kHz I. F. This signal is fed from the mixer through the 5. 5 kHz bandwidth Mechanical filter (CF1) and back into the TCA440 I. F. amp. The amplified signal is rectified by diode D2 and appears as audio across the volume control (RV4). Automatic gain control is not normally used in a direction finding receiver (this would mask the effect of rotating the aerial) so the gain of the R. F. and I. F. amplifiers are set by a fixed, stabilized voltage ( about 0. 7 Volt maximum ) from trimmer resistor RV2. Adjustable audio levels are fed from the volume control to a single, high gain audio amplifier which drives the headphones to adequate level. Medium to high impedance headphones are preferred. TR4 with L3 form a simple Beat...
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The circuit described here uses ultrasonic oscillations and operates based on the propagation velocity of these oscillations in the air. Thus, we can easily determine the distance of two points if the time within which the wave travels this distance is....
Sometimes the precious metals are hidden too deep and are not detected except with complicated devices. In many cases, however, small pieces of precious metal buried near the surface can be detected by relatively simple means. Everyone is very attractive to....
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This Amplifier was designed to have the following specifications: Distortion less than 0.1% at full power of 100W even at 20KHz. Power has to be attributed to an extended bandwidth. The output transistors must be protected against short circuits. The power....
A series of LEDs serve to alert the gardener when plants need water. Using two conventional digital integrated LEDs and a series of LEDs, we make a very useful device for gardening. The device detects the amount of water in the pot and alerts the grower.....
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