Manual Reference

We have already published designs that use a transistor junction operating in Zener breakdown as a noise source. Anyone who has experimented with a reverse-biased transistor knows that the amplitude of the noise voltage generated in this manner is strongly dependent on the supply voltage. The variation between individual transistors is also rather large. An obvious solution is to use an adjustable supply voltage for the noise generator stage. A BC547B starts to break down at around 8V.

Circuit diagram :

Optimised Semiconductor Noise Source Circuit Diagram

Using P1 and R1, you can adjust the voltage across T1 and R2 between 8 and 12V. C3 decouples the reduced supply voltage. An impedance buffer in the form of T2 and R3 is added to the circuit, to prevent the connected load from affecting the noise source. This buffer is powered directly from the 12-V supply. To adjust this circuit, connect the output to an oscilloscope. Then adjust P1 to obtain the highest signal amplitude, combined with the best ‘shape’ of the noise signal. The output voltage is approximately 300mVpp, and the current consumption is around 2mA.

Source : www.extremecircuits.net

VHF UHF Low-Noise amplifiers circuit can be designed using the MAX2664 and MAX2665 ultra-compact LNAs for VHF UHF applications.These devices incorporate a broadband LNA with an integrated bypass switch. The MAX2664 covers the UHF frequency range from 470MHz to 860MHz, and the MAX2665 covers the VHF frequency range from 75MHz to 230MHz. Each device has a zero-power bypass mode for improved high-signal-level handling conditions.Both ICs has a high gain around 15dB and require a single power supply , that can provide an output voltage between 2.4 to 3.5 volts .VHF UHF Low-Noise amplifiers has a very low current consumption of 3.3 mA and can be used in applications like : Smartphones/Handsets , MP3 Players , Home Audio/Video and other portable navigation devices .


VHF UHF Low-Noise booster circuit