Preamplifiers
Low noise preamplifier
A preamplifier circuit with a very low noise characteristic can be built by simply combining a FET transistor with a bipolar one.
The input impedance of the preamp circuit is almost the same as the gate impedance of the FET transistor (around 1MΩ) The output impedance at the other end is about 1KΩ.
The frequency of this [...]
Preamplifier scanner
This circuit scan all the preamplifier entries to identify where is a audio signal and that entry remains selected. After a sign of signal absence, scanning resumes. Scanning action is supported by rectangular signal generator IC2c. Scanner’s entries are connected to the audio entries from volume control board of the preamplifier.
Useful signal is [...]
Preselector for SW receivers
The entry low capacitance of MOSFET modern, with two gates, will create negative inverse reaction through a uncoupled source resistor. Applied right this technique allows the creation of a entrance RF stage field with a relatively high dynamic range.
Radio amateur working on short wave: there is no need to tell, in the days of our [...]
