Circuit Diagram Knowledge: RF

Showing posts with label RF. Show all posts

Wednesday, November 19, 2014

144 MHz Simple RF Detector Circuit

This simple circuit helps you sniff out RF radiation from your transmitter, improper joints, a broken wire or poor equipment with RF shielding. The tester is designed for the radio band amateur 2 meter (144-146 MHz in Europe). The instrument has a reading of 4-step LED and an audible alarm for high voltage radiation. The RF signal is received by an antenna and made to resonate by C1-L1. After rectification by the diode D1, the signal is fed to a two transistor Darlington amplifier HighGain, T2-T3. Assuming a 10-inch telescoping antenna using the RF level scale established for the LEDs is as follows:

When all the LEDs light, the (optional) UM66 sound / melody generator chip (IC1) also operates and provides an audible alarm. By changing the zener diode values of D2, D4, D6 and D8, the step size and duration of the instrument may change as needed. To operate in other bands of ham or PMR, simply change the network-L1 C1 resonance.

For example, a transceiver 5 watt handheld equipped with a telescoping half-wave antenna (G = 3.5 dBd), there is an ERP (Effective Radiated Power) of just 10 watts and an emf of more than 8 volts near the head. Inductor L1 consists of 2.5 turns of 20 SWG (approximately 1 mm in diameter) enameled copper wire. The inner diameter is approximately 7 mm and no core is used.

Trimmer capacitor C1 associates is adjusted for the greatest number of LEDs to light at a relatively low fieldstrength position for a 2 m transceiver 145 MHz transmission. The tester is powered by a 9 V battery and consumes about 15 mA when all LEDs are on. Must be enclosed in a metal box.

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Wednesday, October 15, 2014

Simple RF Transmitter for PIR Sensors Circuit Diagram

This is the Simple RF Transmitter for PIR Sensors Circuit Diagram.

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Thursday, October 2, 2014

Simple Wideband RF Amplifier Circuit

The feedback circuit is formed by RF transformer Tri. The input and output impedance of the preamplifier is 509 for optimum perform- ance. Network Rs-Cs may have to be added to preclude oscillation outside the pass-band, which ranges from about 100 kHz to 50 MHz.
This circuit is of the second kind, using an RF power transistor as the active element.
Feedback is also required to ensure correct termination . (50 Q) of the aerial, since bipolar transistors normally exhibit a low input impedance.
The input winding is l turn, the out- put winding 5 turns with a tap at 3 turns. is formed by RF transformer Tri. The input and output impedance of the preamplifier is 509 for optimum performance.
Network Rs-Cs may have to be added to preclude oscillation outside the pass-band, which ranges from about 100 kHz to 50 MHz. The gain is approximately 9.5 dB, the noise figure is between 2 and 3 dB, V and the third-order output intercept point is at least 50 dBm. The input/output transformer is wound on a Type FT37-75 fer- rite core from Micrometals. The input winding is l turn, the output winding 5 turns with a tap at 3 turns.
Also, the noise figure is not increased because virtually no signal is lost. The common base amplifier is based on a UHF class A power Q transistor Type 2N5lO9 from Motorola.
The gain is approximately 9.5 dB, the noise figure is between 2 and 3 dB, V and the third-order output intercept point is at least 50 dBm. The input/output transformer is wound on a Type FT37-75 ferrite core from Micrometals.
A linear RF amplifier can be made in two ways: (l) with the aid of a linear active element, or (2) with a non-linear element operating with negative feed- back.

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