Post · bonfire.cafe

This is my 2m band #HamRadio antenna amp I designed. It's quite different from my experiments a week ago. This one is a cascode layout with two BFR193s, a nearly perfect 50 ohm match on both sides across the whole band, and just shy of 18 dB of gain. Tuned with S-Params.

In theory! Now to build it and see how close I can get.

If you are looking at learning RF circuit design, take it from me: skip LTSpice and download Qucs-S. This is a really nice piece of software. #AmateurRadio

A circuit schematic showing a 2m ham radio band small signal amplifier and S-Parameter charts for stability, gain, and impedance.

remcycles

@remcycles@subdued.social replied · last month

@relistan Very cool! I failed to simulate an oscillator with Qucs years ago, so maybe I should try Qucs-S next time I need a sim. Good to know it also supports s-parameters.

Karl Matthias 🇺🇦

@relistan@mstdn.social replied · last month

@remcycles thanks!

Karl Matthias 🇺🇦

@relistan@mstdn.social replied · 2 months ago

Also, those are some TINY transistors.

Gary @N8DMT

@n8dmt@mastodon.radio replied · 2 months ago

@relistan Small parts forces the trade between making overall circuit tiny and keeping it big enough to work on (while unfortunately increasing parasitic effects).

Have kept it small in the past, but had to totally do over multiple times as learning occurred. Good prototyping and soldering practice. 😎

Karl Matthias 🇺🇦

@relistan@mstdn.social replied · 2 months ago

@n8dmt I can understand that. Yeah I soldered up a board with one of these to try things out. The 1206 size seems a good compromise for now for the resistors and capacitors. But these transistors are SOT323. Only 2mm on the long side. I managed it but no soldering awards will be won, for sure. We’ll see how it goes when I try this circuit for real.

Graham Sutherland / Polynomial

@gsuberland@chaos.social replied · 2 months ago

@relistan nice design! any idea if Qucs-S supports specifying S-parameter models for MLCCs?

Karl Matthias 🇺🇦

@relistan@mstdn.social replied · 2 months ago

@gsuberland thank you! Hard work getting there 😅. Hopefully I can do the design justice with a soldering iron.

Good question re:MLCCs. I actually don’t know. There are many layers I’ve just scratched the surface of. I picked it over regular Qucs because of the ngspice support. Anything you can do there it can do, too, but with nice UI.

Graham Sutherland / Polynomial

@gsuberland@chaos.social replied · 2 months ago

@relistan ooh, that's good to know, I've been meaning to find a good ngspice frontend anyway.

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