[Amps] HV MOSFETs for RF

[Catherine James]

It's been very interesting to see that many users have strict linearity requirements.  I'm quite surprised that given all that industry experience, we still see ham rigs and amps with poor IMD and thoroughly outdated design techniques.

The users listed include the military, government labs, satellite ground station, commercial transmitters, and so forth.

One possible answer is that none of the uses listed by contributors to this thread are consumer products.  Consumer products will always be more price-elastic, and up-front costs will play a larger role vs. repair and replacement costs in driving decisions.  Industry and government are more able to spend more up front in return for lower lifecycle costs.

The problem seems to be that no other consumer products have a similar need for high power, and non-consumer devices are more willing to run at low efficiency with huge heat-sinks and cooling systems.  The non-consumer products aren't as willing to trade off other things for "inexpensive".

Manfred gave some good insight, which I excerpt below:

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There are two approaches: Either live with those problems, or use some high efficiency scheme to avoid them.

The "live with them" approach typically means using devices with high power dissipation rating at quite low power output. (BLF188XR has 85% efficiency in some applications, but only 29% efficiency in linear mode)

And the other group uses high efficiency techniques, like the Doherty method, Kahn's EER, or direct baseband PWM.

It has been with us for many decades, and the only thing we need to do is come up with a practical, inexpensive, good, hopefully reproducible design, that puts out legal limit power, using some of the recent high power devices!

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73,
Cathy
N5WVR