[RTTY] Bright Idea #99

[Kok Chen]

On Dec 19, 2004, at 3:43 PM, Jerry Flanders wrote:
> A few years ago QST ran an article on a class "E" amp (might have been 
> "D"). VERY efficient - better than 90%, I think (so cooling problems 
> are minimized). A "switcher" at the operating freq, as I recall.

There have been a few articles on Class E amps in the past couple of 
years of QEX, mostly from a Caltech bunch (bachelors and masters 
theses), and one or two of them have been watered down for QST 
consumption.

The operating principle is not like the Class D (basically pwm, I 
think); Class E instead turns the transistor on right at the point the 
tank circuit has swung the voltage across the source/drain to zero, 
thus dissipating very little power in the transistor itself.

But take a look at the amount of current flowing through some of the 
capacitors -- in one case they had to parallel a whole bunch of caps 
together because a single one would run so hot it melted the solder the 
surface mounted cap itself was mounted to the circuit board with :-).  
And they seem to need a keyed power supply in conjunction with the 
input CW, which might be easier on RTTY using a PTT relay.  But I 
suspect you may need to drive the amp with FSK that is phase continuous 
as it switches between mark and space; you might lose some efficiency 
during the mark/space keying otherwise.

The good news is that QEX is available in pdf form on CD-ROM and you 
can find the index to past articles at the ARRL web site.

73
Chen, W7AY