Recent Posts

1 transistor CW – filter

You cannot get it more simple than this, a 1 transistor CW filter. This filter is build according to the (surprise !) Multiple Feedback BandPass Filter (MFBPF) topology. Below, you see the circuit, originally designed by KE3IJ (alas now SK).

Transistor R1, R2 and R3 together with C1 and C2 form the standard MFBPF […]

40m DC-receiver – What’s next?

Now that the basic receiver is working, what do I want to add to consider the receiver ‘complete’ ? This is the current set-up :

The following things I would like to add:

S-meter : shows the strength of the received signal. Based on AF signalCW filter : Multiple Feedback Band-Pass filter, 1 or […]


An attenuation network is often used in devices like a (digital) voltmeter, in oscilloscopes, etc. It offers the possibility to expand the input range of the measurement tool and thus makes it more versatile. Usually the attenuation network is build with a couple of resistor as shown in fig. 1. If the input resistance […]