I made the next try for a DIY FET probe usable to 1.2GHz. An improved PCB and filter worked quite nicely, and is usable to 1.2GHz, all that for just a few €.
Not convinced ? Look at this:
Not too bad for a homebrew part. More details can be seen below:
Click here to see some Commercial and Homebrew High Frequency Probes …
I wanted to make an automated solution for power supply stability measurements which would allow noninvasive measurements on PSU circuits, without opening the control loop and inserting an injection transformer like I have done in the past.
The trick here is to measure the output impedance of a PSU by injecting a known AC current and measuring the AC voltage change, both directly at the PSU terminals. Thus, the PSUs complex output impedance can be derived by Voltage/Current, measured by a scope (amplitude ratio plus phase). The gain and phase curves can be derived from this measured value.
Like the “Noise Figure Measurement Solution for the Poor” this project should end up with a little box containing the measurement electronics, plus some supporting software automating everything else.
Click here to see a Loop Stability Measurement Solution for the Poor …
… and the noise figure project can be seen here:
Click here to see a Noise Figure Measurement Solution for the Poor …
Simple nonlinear circuits can show unexpected und surprising complexity. I tried some varactor frequency divider (2 LC tanks, 1 diode, 1 resistor), and this very modest thing (shown at the top right of the picture) can create subharmonics (OK for a divider), but also chaos, like this:
Similar phenomena can also occur in less exotic circuitry like RF power amplifiers.
Click here for a Discussion of Making Chaos and some Practical Implications …
Apart from a lot of practical projects, I do have some interest in the underlying principles of electronics and electronics measurements as well. If I find some problem interesting from a theoretical point of view, I’ll document my understanding of the problem and possible solutions in a separate section.
Comments, critique and ideas are most welcome. Nothing (including my own products) is too silly to be published and considered here !
The first problem I had mind is how strongly nonlinear systems can be measured using a VNA, maybe by an extension of Keysights X-Parameter method.
Click here to see a Discussion about Measuring Nonlinear Circuits on a VNA …
For sensitive measurements, I needed a FET probe with very small capacitance and a frequency range of up to 1GHz, if possible. Of course, you can buy things like this, but they will have some shortcomings as a very limited voltage range (the faster ones only go up to a few volts), high sensivity to static discharge or even very short overloading, and an ugly price tag in the range of a few k€.
I wanted something robust, cheap and easy to use part instead – ultra precision was not important. When you look at the geometry of commercial probes, it is really hard to believe why things like this should deliver tenth-dB flatness values up into multi-GHz ranges. Most are used in digital environments anyway, and 10bit amplitude precision is unimportant there.
So, lets DIY this and see how far we get !
Click here to see some High Frequency Probes and Measurements …
I, (a long time ago, while being an EE student at the technical university of Vienna, Austria) read about parametric amplifiers and converters and got fascinated by the elegant principle of lossless, ultra low noise power conversion from one frequency to another. I decided to do a project of an LF upconverter as my master thesis, and it worked, but after quite some time of intense fiddling and prototying. Shortly after that I switched into the IT business, got completely absorbed there and did not do any electronics activity for more than 30 years.
Now, I’m back, and I wondered if (given a park of nice RF T&M equipment I did not have when I was a student) it would still be a challenge to make a Paramp in 2018. The result are:
- It is still a challenge. Nonlinear, time varying differential equations always are.
- Theory is plenty and elegant, but of limited use predicting circuit performance
- Results are usable, but at least today can be achieved by simpler circuits.
What I made was a parametric upconverter from the 40m band amateur band to a frequency of 73 MHz, which can be received by standard ham radio models like the ICOM IC-7300. I will ask some ham colleagues of mine to try this out in heavy IMD environments and tell me if this is useful today.
Click here to see some General Information about Parametric Amplifiers …
Click here to see a Parametric Upconverter for the 40m Band …
Probably an old hat for many, but new for me (from a practical point of view) I made my first steps into antenna design. I never was good at, I forgot it instantly after passing the exams. But anyway – ham radio without an antenna just does not work.
The antennas I have built (see link below) worked in practice, but I had no profound idea as to how. After buying EZNEC 6+ from Roy Lewallen W7EL and a seminar held by Chris OE1MVC my intellectual nakedness regarding antenna matters has been partially removed, so I hope.
Click here to see some Active Antennas I have Built, now with EZNEC Simulations …
Thanks again to Roy and Chris for the good support and the enlightning discussions !