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The RF Workbench / Re: Redhat's LULU build attempt
« on: January 16, 2023, 1953 UTC »
I didn't watch the whole thing but I did go through probably the high points. I'm fairly sure that you know this already but for the other folks watching, the reason why you have ended up lower in frequency is the unavoidable presence of parasitic capacitance on your "hand carved PC board."
The online calculators to determine component values are all fine and good*, but you have to understand that the models can't incorporate PCB parasitics because the the parasitic values depend upon the PCB layout, the PCB materials, the choice of transistor, the packaging of the transistor, etc. They work OK as starting points but there will be refinement later. This is why I recommend the "driving a car in deep snow" method: https://www.hfunderground.com/board/index.php/topic,92791.msg297947.html#msg297947 Make your first try, figure out how far off target you are and then make course corrections to get closer to the goal.
And, yes, as I heard you say in the video, Class E can be very picky about component values on the matching network. Whatever values you come up with may be suboptimal for someone else whose "hand-carved PCB" technique is a little different from yours. This is one place where a manufactured PCB may be helpful since it is likely to be more uniform from batch to batch, though that is not guaranteed either. (FR4 Er can be all over the map.)
Unless I missed it, you didn't show what the drain waveform at the frequency where the power output peaks (~5500-5600 KHz?). If the drain waveform looks kinda/sorta OK there, then I think your problem is simply a tuning issue and not anything else.
One more thing: if your PCB is dual-sided copper PCB material, you can try to cut away some of the bottom copper directly under the active components and the tuning/matching network. This may dramatically reduce the parasitic capacitance to ground. (On a quasi-related matter, on microstrip and grounded-coplanar waveguide, removing ground will raise the characteristic impedance of a transmission line for similar reasons.)
* Here's another one, also from Australia: https://people.physics.anu.edu.au/~dxt103/calculators/class-e.php
The online calculators to determine component values are all fine and good*, but you have to understand that the models can't incorporate PCB parasitics because the the parasitic values depend upon the PCB layout, the PCB materials, the choice of transistor, the packaging of the transistor, etc. They work OK as starting points but there will be refinement later. This is why I recommend the "driving a car in deep snow" method: https://www.hfunderground.com/board/index.php/topic,92791.msg297947.html#msg297947 Make your first try, figure out how far off target you are and then make course corrections to get closer to the goal.
And, yes, as I heard you say in the video, Class E can be very picky about component values on the matching network. Whatever values you come up with may be suboptimal for someone else whose "hand-carved PCB" technique is a little different from yours. This is one place where a manufactured PCB may be helpful since it is likely to be more uniform from batch to batch, though that is not guaranteed either. (FR4 Er can be all over the map.)
Unless I missed it, you didn't show what the drain waveform at the frequency where the power output peaks (~5500-5600 KHz?). If the drain waveform looks kinda/sorta OK there, then I think your problem is simply a tuning issue and not anything else.
One more thing: if your PCB is dual-sided copper PCB material, you can try to cut away some of the bottom copper directly under the active components and the tuning/matching network. This may dramatically reduce the parasitic capacitance to ground. (On a quasi-related matter, on microstrip and grounded-coplanar waveguide, removing ground will raise the characteristic impedance of a transmission line for similar reasons.)
* Here's another one, also from Australia: https://people.physics.anu.edu.au/~dxt103/calculators/class-e.php
