This filter was designed to filter the 1kHz frequency of the telemetric signal from environmental noise. The filter itself is straightforwardly built with acceptable electronic parts worldwide. This filter can be used in any circuit because of its simplicity.
The circuit contains a minimal amount of parts, including one general-purpose NPN transistor with coefficient 50…70 and more. Such filter blocks may be connected in series directly one to another(second IN first OUT). This way, filter gain may increase up to 1,2…2.
Bellow is a filter transfer function that consists of four cascade-connected filter nodes:
As you can see in the picture, filter level -3dB is at ±250Hz from 1kHz. While at ±350Hz, it reaches -6dB attenuation.
Filter drains about 0.5mA of current when three nodes are connected in series.