Adjustable gain LNA
Low noise amplifiers are very useful. I built one with single BFG425W transistor with adjustable bias current. The schematic diagram is very simple:
and the PCB is 20x24mm:
I first soldered prototype with smallĀ islets cut from FR4 PCB:
Preliminary measurements were promising. Then I etched final design (here is 1:1 artwork for toner transfer) and assembled the module. Here is comparison between prototype and final module.
I added small metal cap to cover the amplifier active part. It was salvaged from an old mobile phone.
Here are measurements:
The amplifier is intended for lower bands including VLF. I tested the lowest usable frequency, which turn out to be 75kHz. Such amplifier is therefore suitable also for amplifiaction of the e.g. DCF atomic clock signal.