[AMRadio] Re: [AM Radio] 360 Watt class E transmitter - modified design for new MOSFETs

[Steve Cloutier, 978-597-3311]

At 11:21 AM 8/22/2002 -0700, you wrote:
>Does anyone have an audio file (.mp3 or .wav etc) of one of these 
>transmitters?  Being VERY new to AM and having a burning desire to build 
>something that keeps the smoke inside the parts, I would like to venture 
>out on this project!

Hi!

These babies sound REALLY good.  I've built LOTS of transmitters - PDM, 
series modulation, phase-to-amplitude - you name it, I've probably built it 
over the past 30 years or so :-)  I have *never* before built any 
transmitter which is as good as the current class E setup, with the class H 
modulator. And, it is reproducable.  Bob, K1KBW is operating this setup, 
and it sounds just fantastic.  The reason these things can sound so good is 
that there is nothing whatsoever to limit the frequency response or 
linearity.  There are no transformers, no high resistance devices, and in 
the case of class H, no switching (aliasing) products.  So, it's just about 
as good as it gets :-)

On the microphone (VERY important and a good question!), I use a condenser 
mic from Radio Shack - just the element (which costs a couple of bucks or 
so) mounted in an old microphone case.  I've been using this microphone for 
YEARS :-).  GREAT frequency response (down to a few cycles per second!) and 
real clean.

Any MP3 or similar file you might hear will be subject to the restrictions 
and limitations of the receiver in use at the time.  The detectors of most 
receivers leave much to be desired in the distortion department (this can 
spark a whole discussion just about receiver detector circuits - an art 
unto itself - with real experts to tell all (I am FAR from an expert in 
this area, although I did build a nice low distortion detector for my 
homebrew receiver). So, just something to think about, that's all...

With transmitters, I tend to like to use real measurements - waveforms, 
etc. to first prove audio designs.  Then add the equalization, etc. which 
is quite important to the overall "sound".  So, if a transmitter will 
modulate a triangle wave correctly, a square wave without tilt, and a sine 
wave, it's generally going to sound very good.  Very few transmitters are 
able to successfully (and without distortion) modulate a 400 cycle triangle 
wave, a 50 cycle square wave, and a sine wave from 20 to 10kHz with a more 
or less flat response.  The class E transmitter using the class H modulator 
described at the class E web site can do all of this.  It's not because my 
particular designs are so wonderful, it's just due to the fact that all of 
the limiting factors, by the very nature of class H, are eliminated.  It's 
just easier to get good sound.

Anyway, there's some info to chew on :-)

Regards, and talk later.

Steve