Showing posts from December, 2021

A bit of Maths

Having another go at calculating the optimum output match for a generic LNA I had a play in MatLab, but being less than familiar with MatLab I wanted to double check my results. Perl is an easy to use programming language, and has an extenion for complex numbers, which makes things easy.  Supplying the input gamma, along with the S-parameters for the optimum input match for minimum noise from the datasheet, this attempts to calculate the optimum output match from the formula:  It is reasonably simple to use Perl to calculate this once the Math::Complex library is loaded, complex numbers can be manipulated with the same ease as real numbers, thanks to the wonders of operator overloading. To check the program, the values from the  paper which included a worked example. However when I ran the calculation, I did not get the published results ...infact, it was not even close ... and after two days of head scratching and questioning whether I could even do basic maths, I posted the question

13cm LNA design.

 When I did my electronics degree, all those years ago, I wasn't really paying much attention to RF design, so I've had to learn a lot of this from scratch, as I failed to pay sufficient attention way back then. I thought I would have a go at building an LNA for the 13cm band as I had a transverter that didn't really seem to perform as well as I wanted. 13cm/2320MHz is high enough to be interesting for design, yet should still be accessible with FR4 substrate for the circuit boards. Certainly, for higher bands, PTFE substrates are becoming more appropriate, but 13cm should still allow FR4, and as my initial attempts are likely to be needing fine tuning, FR4 is a much more "experimenter friendly" choice. There are essentially 3 parts to the design and evaluation process:            The basic schematic with the bias circuitry.          The RF design          Performance evaluation. The basic schematic and bias  scheme were as a result of my choice of active device f

KST2YOU - An alternative interface to KST

  If any of you use KST and want to try a slightly (hopefully) more friendly user interface, I have published one here:   Amongst the design requirements were that it should run from a phone or tablet, as I really can't be doing with dragging a laptop around for portable trips for microwave stuff. It all runs in a web browser, and obviously on any desktop with a web browser.   If you already have an account on KST, you can just log straight in, you usual username and password will work.   The message interface is familiar to you if you have used KST, however I've tried to fix a few of the oddities of the traditional KST interface. One of the problems in a busy contest day is if you are trying to organize contacts say in the north of England and have range of at most 300km, you probably don't need to see messages from stations chatting in Italy.  The "filter by distance" option allows you to ignore chat from stations beyond a certain di