First Results from the LM723 Self-Heated Reference Long-Term Tests


LM723ChipPictureAfter more than a month of observing my silly LM723 self-heated reference circuit the first results have arrived:

  • the first 1000h drift ist about 100ppm (the datasheet typical value is 500ppm typical)
  • there seems to be no significant room temperature dependency

Further tests will show if the drift rate slows down over time and how much.

Click here for Silly Circuits – A Heated LM723 Reference …

RF Filter Gallery Opened

I collected a lot of filters and diplexers I have made and felt that it was high time to provide some documentation for them before all the designs drift off to oblivion.


All of the designs have a schematic, a simulation, a PCB, measurements with a VNA and photos of the actual hardware. So, enjoy, maybe you find something usable !

The filters I made range from the 160m HF band up to 23cm. All are low to medium power, and all fit into a small Schubert tinplate box, and all have edge-mount SMA connectors. They should be easy to reproduce.

Click here to have a look at the RF Filter Gallery …

Testing a DATONG PC-1 Parametric Converter


I finally got hold of one of this very rare and exotic parametric converters from the late 70ies. I was really curious if Dr. Tong had used some long forgotten tricks to create a top performance receiver for the time. To make it short – No. This thing has no gain, a moderate IP3 and noise performance, but it worked OK. Building style was a bit on the cheap side, but this was an affordable part for 120 GBP (in The Shortwave Magazine, April 82).


Click here to see more on Parametric Amplifiers …

A Noninteger Frequency Divider with Sinewave Output



A radio amateur colleague asked for help on a noninteger frequency divider for use in his atomic clock comparison project. It sounded interesting, so I gave it a try. Although premium performance was not required, I took it from the sporty side and I wanted to see what could be realised using common off the shelf components and a careful design.

Click here to see a Noninteger Frequency Divider With Sinewave Output …


Silly Circuits – Battery Savers



I needed a battery saver, voltage monitor and a stabilizer circuit that would not create any AC interference from clocked logic, as small it might ever be. The purpose was to power some ultra-sensitive equipment that could easily detect even well filtered clock signal interference.

This meant a pure analog design – awkward in 2018, but it does the job.

Click here to see Self-Quenching Battery Timers and Power Conditioners …