Lately I have been asking myself if I should bite the bullet and just go class E. For mediumwave it is a sure fire bet that it will work great. Issue I have with it is that most class E designs are frequency specific. It is more work to go with class AB linear to amplify a modulated exciter, but if designed right and not asking for too much power output it can be made for much wider band operation and reasonable efficiency and will require far less output filtering compared to class E. Once you get beyond a few 10s of watts carrier with linear amplifiers it just doesn't become practical anymore since the heat generated and the efficiency being so low starts to show its ugly head. Class E amplifiers carry their own set of issues though, one being how touchy they are in design practice in my opinion. Also if you want an amp that covers a wide range for multipurpose use it becomes and issue with output filter tuning. The most sane way to go about this is to either outright use class E if you only plan on using one frequency for transmission so you can fine tune it to that, or use a class C amplifier that has modulated power going to it, aka: high level modulation. It becomes questionable though if class C used in that respect is actually more efficient than class AB given that you have to factor in the heat and power generated by the modulator which many people rarely do.
Class E is a piece of piss. The only reason anyone would think it was difficult is coz they've never done it before. In reality it's way simpler than class AB and similar to C but even more efficient. It's a no brainer. Also the though of using 3 chips to make a PLL is so old ffs. DDS has been around for years and again a no brainer. Likewise the mere mention of a modulation transformer makes me cringe.
Class E is a piece of piss. The only reason anyone would think it was difficult is coz they've never done it before. In reality it's way simpler than class AB and similar to C but even more efficient. It's a no brainer. Also the though of using 3 chips to make a PLL is so old ffs. DDS has been around for years and again a no brainer. Likewise the mere mention of a modulation transformer makes me cringe.
Time to move on.
CLASS E + DDS + PWM.
VERY SIMPLE = VERY GOOD!
stretchyman2k@googlemail.com.
Well given that this is an old thread much of my experience experimenting with and building transmitters confirms your position that Class E RF with PWM modulation is the way to go for simplicity and efficiency.
One thing I think you may have overlooked is that the OP was asking about amplifying his transmitter linearly given what he had at the time to work with. Of course there are far better ways to setup a broadcast transmitter but sometimes people work with what they have and learn along the way.
Another point is that many of us come from a background in RF where tubes were king and class C and high level transformer modulation was the standard so moving into Class D/E designs is a whole new ballpark relearning how the final output impedance is transformed and filtered, how to drive the gates properly, and then the digital aspect with the fet drivers and DDS which might not be common knowledge to those who were use to older technological concepts of RF.
I realize you are trying to sell transmitters and I see why you think what you do about the simplicity of Class E designs. Heck I do too after building a few of my own now, but I hope you realize not everyone started there or has the means to at a given moment. That's not even including the guys who like to use boatanchors or classic designs on purpose for whatever nostalgic reason they have.
PS: The old three IC PLL may be ancient but it works and many of us already have those parts in our bin so if they want to whip up the circuit quick and get something working what is the harm? Even with the latest remake of that old PLL chip like the TI 74xx 4046 series it's possible to get frequencies up to 16MHz which makes it possible to divide that to drive a push pull Class E stage from say 100kHz to 8MHz. Not bad for a 3 chip solution that many people have laying around waiting for a fun midnight project.
People do what they do because it's fun, educational, or because it is within their means and part bins. Not everyone goes for the most modern design for simplicity and cost to sell a product so of course it would be silly to someone doing so like yourself given the hassle.
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