Richard Clark wrote:

On Fri, 04 Mar 2005 01:13:39 GMT, "Thomas Magma"
wrote:

Wow this is a long thread. Don't really know where I should put my two bits
in, but here it goes.

I have designed several RF PA sections in the past. 500MHz at about 50W.
Pretty easy stuff if you have the right tools and know how to use them. The
tools I like using for matching the power output FET is two triple stub
tuners. One on the input of the FET and one on the output. So it
goes...pre-amp (50 ohm output) - stub tuner - FET - stub tuner - 50 ohm
dummy pad - spectrum analyzer. Then just tune the stubs for the performance
you desire, these include: efficiency (thermal issues), harmonic content,
spurious emissions, load VSWR considerations, cold start, ect. Then remove
the FET and look into the triple stub tuners with the network analyzer.
Model and duplicate the network out of discrete components that can handle
the voltage/power, send the design off to the enviro test lab, and head home
early for the day.

Cheers,
Thomas

Hi Thomas,

Thanx, your two bits were worth more than the academic plug nickel.
This is something that our original poster should hearken to as his
needs were obviously production oriented.

I doubt you understand what he wrote. I can't fathom why you would be concerned
with the OP when your own difficulties are so acute.

Bench experience will trump
cut-and-paste theory in a heart-beat.

How would you know?

However, triple stub is pretty aggressive. How long did it take you
to flatten response?

How long will it take you to figure out that he wrote not a wisp of a word on
what the "output-Z" of the amplifier is? He did write that he determines how
the amp was loaded to acheive power, something I've been saying is the prime
concern.