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Re: [Amps] Designing the Cleanest Linear with RF Negative Feedback

To: Karl-Arne Markström <>,<>, <>
Subject: Re: [Amps] Designing the Cleanest Linear with RF Negative Feedback
From: "Tom Cathey" <>
Date: Mon, 19 Dec 2005 16:29:00 -0500
List-post: <>

OK on the caution needed regarding obtaining these high IMD numbers. Good 
advice, OM.

I would say that the level of distortion I heard when listening to the 5mW 
level coming out of the FT-1000D was quite acceptable. At 3kc away, the 
trash went into the noise from a starting point of S9+40 over. When I turned 
it up to 10-15mW, it go noticably dirtier... about at the same IMD level as 
running the 1000D at 150W out.
It appears that the 15mW IMD level is "well matched"  for the PA... :-)  So 
the key appears to be to run each stage at a very low level and/or in class 
A. [5Mw for the 1000D]

ie, If I can get the rest of the linear chain to be anywhere near as clean 
as what the 5mW level is, even 12db worse in total, I will be happy.

Looks like you put in some real effort making up that block diagram. Thanks 
again, OM!!! . I will continue to study it, though, as you said, it may to 
be more than I need for the job. Maybe the 1000D is not clean enough. After 
thinking more, I believe I will build up a Norton pair of transisitors as 
the first stage after the 5Mw and go from there. Probably into a 6550 or 
4CX-350 pre driver, 4CX-350 driver and 4CXXXX final with feedback. That's 
how it stands for now.

We'll see how it goes.  Thanks guys, for all the help and starting me in the 
right direction. This is what I needed, and now I can focus on some real 
world applications.

Also, the archives are fat for the next guy considering a project like this. 
I'll post some results as I progress with building and testing.

73, and the best of  Xmas and 2006 to you all !!

Tom, K1JJ

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