Recent Posts

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 […]

Brickwall audio filter

For my 40mDC receiver, i was looking for a good audio filter that I might reuse for multiple receivers. While browsing in old magazines I came across a filter designed by Robert Penfold. It was featured in an article in Ham Radio Today March 1986 (see download section).

The brickwall audio filter […]

40m DC receiver (2)

After my previous attempt at building a 40m DC receiver failed (I received nothing but noise while at my Kenwood HF receiver, plenty of signals were heard), I made some changes to improve the sensitivity and to add some features that were desperately needed..

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40m DC receiver (1)

The design for this receiver is based on an earlier design by Steve KD1JV. it is build around two analog switches TS5A3157. These switches have on resistance of ca. 5.5 Ohm 10 times smaller as the often used 74HCT4053 switches.

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Gain distribution in DC receivers

For an upcoming 40m (7Mhz) DC receiver that I am working on, I wanted to know the necessary gain. After building the first prototype, the output was kind of quit. So the question came up, how much gain do I really need for a DC receiver? Back of the envelope calculation : to get […]

Sweep control oscillator

The purpose of this device is to help you sweep an audio or rf filter. It outputs a 0..10V sawtooth that can be used to control a sinus/ function generator or an rf generator. Together with a CRO oscilloscope, a millivolt meter and or power meter this can be used to accurately characterize a […]