OK, seeing as my 'Simple SiC TX' post has been somewhat led astray, I thought I'd start a new post..
Having fiddled and tweaked most designs over the years I've found nothing is quite like the LuLu.
I still see posts showing other designs (bless you DM!) but there's nothing to compare to the LuLu.
If you want simplicity and efficiency there's nothing to touch it.
I've done little more than change some of the components to modern variants, the design is essentially the same.
I must apologise if I dont have the same ethics as some determined to use 'Junk box' parts that no-one other than the author posseses!
I will use the latest and best components out there, they're readily available from ALL the major component suppliers, cheap too!
As with anything RF, you cant just put it together and expect it to work, no matter how simple it is, the main 'problem' being one of the 'layout' of the components.
ANY RF design will NOT work on 'Veroboard' and the simplest method is to build above a copper groundplane, 'Ugly style'.
However the best way is to produce a PCB which simplifies the whole process and makes it repeatable.
OSHPARK is highly recommended for this as their quality and turnaround is good.
Learning to use a layout program will take some time, I use EasyPC and have for years as they're a local company.
PCB Layout
Schematic.
I'm no longer using IRF devices as they're too many clones around (of the IRF510) which either dont work and with a Vds of 100V you can only use 14V max and therefore limited to 10W carrier power.
With the SiC and Gan devices you can use 200+V so there's literally no limit to the output power of a single device.
With 14V you'll be able to acheive a 20W carrier and everytime you double the voltage you quadruple the power.
However this is when the Class E is tuned for maximum power and efficiency is fairly low (around 80%).
For maximum efficiency a 5W carrier (@14V) is about right. So at 28V you will acheive a 20W carrier and >95% efficiency.
So with 60V or so you will get 100W with the same high efficiency, clearly this is the way to go if you have lots of volts and want high power.
Whilst the SiC devices are decent the GaN devices (if a little pricey) are amazing and can be driven with <8V on the gates and the same design will go to above 14MHz.
To finish off we need to modulate the RF generator.
There seems to be some 'Mystique' around how this is done and quite simply there are 2 methods.
1, The 'Modulation Transformer' method.
The humblest of modulation methods and fine as long as powers are kept low (<50W carrier) otherwise the 'Mod Tranny' gets a bit silly, size wise.
These so much misinformation about modulation transformers and which one to use etc and the simpest answer is, build your own.
There's 1000's of transformer manufacturers worldwide who stock standard bobbins and laminations for making transformers.
Find one who stocks 'E160' bobbins and lams and use those.
The Mod tran needs to be wound with (approx) a 1:2 ratio, I wont go into the reason for that here but trust me it's right as I've wound dozens and experimented to find the best one too.
I now get them manufactured by the same company I purchased the parts from, a lot less hassle and a decent price too.
So using an audio amplifier, I'm not going to recommend any other than to say for $10 the TPA3116D2 designs all over the web from CH are fine and will push 100W in PBTL mode are class D and very efficient.
Drive the primary of the transformer with the amp (in PBTL aka mono mode), just like it would drive a speaker, the secondary of the mod tran goes between the modulating voltage and the RF generator, this enables the voltage to get waggled up and down with the audio.
Decent BASS response is an issue here as unless the modulation transformer is absolutely massive you will have to limit the low frequencies to 300Hz otherwise the MT will saturate, and genearate lots of heat and distortion.
Limiting yourself to a 20W carrier with the E160 size recommended you'll be fine to 100Hz however.
2, The 'PWM' method.
A somewhat more efficient method that has one 'minor' drawback.
However even the efficiency of this method is a bit of a mute point if youre using a class D amp as the modulator in method '1'!!
Apart from the 'Problem' of having to design/build your own PWM modulator, beause the PWM is in series with the supply and will ONLY allow the voltage to shift between zero and Vcc, you will have to run the carrier at half the supply, you don't get a voltage 'Swing' as you do with a Mod tranny. So if youre limited to 14V then the carrier wil run at half of this 7V and the power ONLY a quarter, so 5W in this design.
Clearly for low voltage systems this is NOT the way to go, but for high power systems with lots of volts it's fine and has no limits regarding BASS response etc and is far more linear & highly efficent, being class D.
There's a little a little trick you can use here and as long as you're happy with a 5W carrier (only having a 14V supply) or have a 24-28V supply, you can directly PWM Modulate the RF by using one of those TPA3116D2 amps run in PBTL mode. Simply connect any of the speaker O/P's directly to the RF, it will have half the supply present and waggle up and down with the audio. Simple eh!
See;
https://www.youtube.com/watch?v=lMMSw0kFHvwFor DEMO.
Please if I may ask this thread is kept with simplicity in mind.
Regards
Stretchy.
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