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Re: [Amps] Tuned Input - IMD and efficiency

To: "Tony King - W4ZT" <amps071806@w4zt.com>,"AMPS" <amps@contesting.com>
Subject: Re: [Amps] Tuned Input - IMD and efficiency
From: "Tom W8JI" <w8ji@w8ji.com>
Date: Wed, 9 Aug 2006 13:26:17 -0400
List-post: <mailto:amps@contesting.com>
> Ok, here we have finally gotten a documented number; 4 to 
> 6 dB HIGHER
> with an untuned cathode driven amp than a tuned input. 6 
> dB is a
> significant amount in my book.

I wouldn't take that number to the bank since the result 
would have to depend heavily on the impedance seen at the 
cathode, how the exciter behaves, and even cable lengths.

> Now it would be nice to see validation of these numbers on 
> real amps
> that we find in use today.

It might be something that never happens because there are 
too many variables.

> It is also very interesting reading in the last paragraph 
> regarding the
> coax used to connect the exciter to the amp.

If it affects efficiency, and I know it does without a tuned 
input or with an incorrect type of tuned input, it would 
also have some effect on IM.

Quite frankly I've never measured the IM change because not 
having a tuned input causes too many other headaches.

I highly doubt a simple shunt capacitor can be effective 
from 1.8 to 30MHz.

73 Tom 


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