[hpsdr] class E

[mike]

Frank,

Are you using the modulators you've been talking about for AM only, or 
do you have EER on the air with SSB?

As for sources (pun not intended) for cheap FETs you might check out the 
ST Microelectronics product line. Mouser has stock of some pretty rugged 
devices in the under $5 each range.

Mike
WO1U

FRANCIS CARCIA wrote:
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> Hi all, Usually a class E final wants a specific drain shunt c on
> each band. I know you can get away with maybe 2 bands but beyond that
> you become class D or inefficient class E. It is actually pretty easy
> to build a final for each band. I would be interested in any
> published data out there. My concern with Penelope driving a pdm
> modulator is the phase shift through the pdm filter. I used a uc1846
> current mode PWM in my 160 meter rig and a discrete modulator in my
> old Viking 2 tube TX. Some of my smarter friends put a bit of bias on
> the gates of a class E final to reduce the drive required. I have not
> tried this yet because I rely on the zero bias to assure less than
> 50% duty cycle drive to my push pull final. This guarantees no cross
> over currents due to the delay differences between turn on and turn
> off of the final FETs. The best cheap FETs out there today are the
> Fairchild FQA11N90s but I hear they are being discontinued. These are
> power supply FETs that work up to 40 meters. I'm working on a linear
> amplifier design and found positive bias with drain current requires
> a bit of source resistance. I just did a design for a friend and I
> put a pair of 1 ohm 2 watt resistors in parallel on each source to
> keep them linear. Also added a bit of RF feedback. The 11N90s seem to
> lose a bit of efficiency at 40 meters but still look linear at with
> the two forms of feedback.. I plan to start with an old 3 stage 100
> watt strip out of an old Raytheon marine rig modified to go to 10
> meters. The IXYS fet line was solt to I think microsemi. They are
> much more expensive but will cover the whole hF spectrum. There are a
> couple different sources of the old Motorola style FETs that drop
> right into CCI boards. frank
> 
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