No-Tune vs Amplifier and Tuner for non-Ham application - Page 1
Forum section: electronics / rf-microwave

author: Plasmateur
author_rank: Regular Contributor
timestamp: February 01, 2021, 10:05:19 pm
content: Hello everyone, I'm trying to build an experiment at home which requires 300W-600W of HF power.If I can get some amount of HF power, I can produce plasma in a vacuum chamber. The current equipment I use in a lap does not allow me to modulate or phase lock the HF signal which produces plasma. So I'd like to use some HAM equipment to enable me to do this. I'm just not sure if "No-Tune" amplifiers can actually do this.This would be my amplifier and tuner setup.1.)SDG2000Xfunction generator2.)10 Watt pre-amplifier3.)350W HF amplifier4.)TunerAnd this would be my setup with a no-tune amplifier1.)SDG2000Xfunction generator2.) Some cheap amplifier that gets me to 100W to drive the next amplifier (doubt it will be cheap)3.)No-tune amplifierSo I'm not sure about the inner workings of a no-tune amplifier. Maybe it works similar to a push-pull self resonant induction heater? I don't know. I'm not sure anyone has experience here producing plasma with HAM equipment or has an intuition on if a No-Tune amplifier could work. Just looking to pick some brains here. Thanks!

author: TheMG
author_rank: Frequent Contributor
timestamp: February 02, 2021, 02:25:54 am
content: No tune just means the amplifier is broadband and doesn't need any tuning adjustments when changing frequency bands. This is true of virtually all solid-state HF power amplifiers.This is in contrast with tube amplifiers, which require re-tuning of the plate and load whenever the frequency is changed in order to maintain optimum operation.With any amplifier, especially solid state ones, you need to keep the load as close to a matched 50 ohm load as possible (minimum SWR). If your load is not a good 50 ohm impedance match, you need a matching network (an antenna tuner is essentially a form of an adjustable matching network).An other important point to keep in mind is that most ham HF amplifiers are not intended for continuous duty. Most ham solid state amps will overheat after a few minutes at full power output. These amplifiers are linear so are not very efficient (lots of heat) and don't have the necessary cooling for continuous high power operation.For plasma generation you don't need a linear amplifier. A class C or E amplifier would be much more efficient, more suitable to this type of application.

author: fourfathom
author_rank: Super Contributor
timestamp: February 02, 2021, 05:39:02 am
content: Quote from: TheMG on February 02, 2021, 02:25:54 amYes, but this particular amplifier uses frequency-sensing to select a switchable low-pass filter section (to attenuate harmonics.) I don't know if this is designed for just the ham band frequencies, or if it will work over the entire HF range.Quote from: TheMG on February 02, 2021, 02:25:54 amVery true. What is the impedance that the power amp will be seeing?Quote from: TheMG on February 02, 2021, 02:25:54 amAgain, true, but it might be hard to find an off-the-shelf class C or E amp for the HF region, and these amps are definitely *not* broadband.

author: Plasmateur
author_rank: Regular Contributor
timestamp: February 11, 2021, 01:59:42 am
content: Thank you both for helping me with this project. It turns out I will have to build my own matching network for this application, which is simply made from two tunable air dielectric capacitors. Also, I was able to find some very cheap but quality components to build a 600W, wideband amplifier. Now I'm just trying to learn how the circuits work, which will be in another post on these forums. Thank you so much.