Recent Posts

Easy to Customize Universal Low Pass Filter

PA3COR - Universal RC Low Pass Filter fc = 3.3KHz

A universal low pass filter that can easily customized, uses easy to obtain parts and has low power consumption. […]

40m DC Receiver – CW Filter

So after studying some designs of multiple feedback band-pass filters for CW by other designers (see my previous post), I’ve decided to try my hand at designing and building one myself. Actually, I’ve made two different versions. The first one is designed by myself and is a two stage filter with an fc of […]

Soundcard Interface

Coming soon

Multiple Feedback Band-Pass filter

Band-pass filters are filters that are designed to let only a certain set of frequencies pass through. Overtime a myriad of different topologies have been developed by some very creative designers. Passive vs active, RC-filters vs LC filters, combinations of low pass and high pass filters, with gain and without gain, etc. One of […]

40m DC-receiver – VFO

So the receiver is alive and kicking and I have received amateurs from The Netherlands, UK and Italy on a simple 10m wire antenna. However, the VFO is comprised of a Siglent SDG1032X function generator from work. Hardly a self-contained solution!After an article by Bill Merea in the GQRP Sprat magazine, I’ve decided to […]

Milliohm meter

This is a simple but accurate milliohm meter with a range of 0 – 2000 milliohm (= 2 Ohm). It has a typical accuracy of 2%-3%. Unlike other designs this circuits doesn’t use large currents to measure these small resistances. So there is no risk to damage components. A small alternating current is used […]

40m DC receiver – “It’s alive!”

With a three day Pentecost weekend and my wife away on a camping trip with my son, I had some time to look into the receiver again. With the previous series of tests, I’ve found that product detector was working fine and featured good conversion gain. The LO oscillator injection was flawed because the […]

Double-balanced cross-coupled product detector

The double-balanced cross-coupled product detector had a brief stint of popularity in the 70s and 80s. It’s popularity quickly faded once integrated product detectors like the Plessey SL640, Motorola MC1496/1596 and the CA3028A came on the market. Offering ease of use and further integration. My attention was first drawn to the cross-coupled product, when […]

JFET testing

For an upcoming RF amplifier project I needed a couple of JFETs. The spread in device characteristics is quit broad. For the BF256B Vp ranges from -0.5 to -8.0V ( a factor 16! ) and IDSS ranges from 6 mA to 13 mA. Since, I bought a small stock of them, I decided to […]

Wienbridge oscillator à la Jim Williams

Jim Williams was probably one of the best and most productive analog designers of the 20th century. He has written many application notes and design briefs in his career as application engineer for Linear Technology. Of course, it featured parts manufactured by his employer. His biggest contribution in the field of analog design, is […]