Winner of the G2NJ Trophy !!!

The G2NJ Trophy is sometimes awarded for a really good technical article, and sometimes for an outstanding contribution to international QRP. This year’s winner described a Cross-coupled Double Balanced Product Detector in SPRAT 191. The winner is Cor, PA3COR”
Steve G0FUW, Sprat 194

Needless to say it was a complete surprise! I feel very honored with this!
I looked up who has been awarded this trophy in recent years and then I felt completely hunbled! I can hardly believe it…

You can find the original article HERE.

NE602 40m DC Receiver

Updated : January 25th; Input amplifier
Updated : January 26th; Audio filter

A couple of days ago I found the circuit of 20m DC PSK31 receiver at the website of va3iul. The website of va3iul is probably well known in the radio amateur community. It features 100’s of circuit design ideas on all kind of topics related to RF design : oscillators, noise sources, filters, phase shifters, it is all there.

Now my google search came up with an image of a 20m PSK31 receiver designed by DG2XK hosted by va3iul. it didn’t state in which magazine it was originally published and it did not show the component values.

20m PSK31 DC receiver by DK2SK
Continue reading NE602 40m DC Receiver

Simple remote numeric keypad with ATmega88

Numeric keypad for radio control
Numeric keypad for radio control
Continue reading Simple remote numeric keypad with ATmega88

Easy to Customize Universal Low Pass Filter

The circuit below shows an active low pass filter that is universally applicable. Only 4 equal (!) resistors needs to be changed to change the filter corner frequency fc. It uses only standard parts, is suitable for a large supply voltage range and needs only a modest 2mA of supply current.

R2, R3 and R4 set the input bias voltage at half the supply voltage. R5-R8 and C3-C6 are the low pass filter network. C3, C4, C5 are bootstrapped to provide a sharper roll-off. Q1 and Q2 are a series-feedback pair and function as a ‘super’ emitter-follower. A standard emitter follower has a gain of ≈ 0.90 … 0.95x. This ‘super’ emitter follower has a gain of ≈ 0.99x. Just like an OpAmp with feedback, in this series feedback amplifier, the feedback increases the input impedance, lowers the output impedance, stabilizes gain and lowers distortion. Not bad for a single €0.10 transistor that is added!

PA3COR - Universal RC Low Pass Filter fc = 3.3KHz
PA3COR – Universal RC Low Pass Filter fc = 3.3KHz
Continue reading Easy to Customize Universal Low Pass Filter

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).

Continue reading 1 transistor CW – filter