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Re: [TenTec] Ten-Tec PA design

To: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Subject: Re: [TenTec] Ten-Tec PA design
From: ron <roncasa@verizon.net>
Reply-to: roncasa@verizon.net,Discussion of Ten-Tec Equipment <tentec@contesting.com>
Date: Thu, 13 Jul 2006 13:34:44 -0400
List-post: <mailto:tentec@contesting.com>
Well put Jerry, I concur (smile)

Ron, wb1hga

Jerry Volpe wrote:

> Ten-Tec has for nearly 30 years included a very descriptive section in 
> their transceiver manuals regarding the effect of SWR on their rig's 
> transistor PA output states and how Ten-Tec chose to not use SWR 
> rollback circuits. Instead they used far healthier transistors (hence 
> the ability to run 100% duty cycle without a fan) and installed a 
> current limiter in either the rig itself, or more commonly, in the 
> matching power supplies. In the Ten-Tec description they refer to two 
> types of SWR, referring mainly to whether or not the ultimate (complex) 
> impedance at the transceiver output is higher, say 100 Zohm or lower 25 
> Zohm. In the first case there are no issues nor protection generally 
> necessary. In the second case, as the SWR increases, effectively taking 
> the output more closely to a condition similar to a dead short, the PA 
> will pull more and more current because of its design. Unless there is 
> some form of limit to the available current eventually the transistors 
> will be operating outside their design temperature range and of course 
> that is not good. This is not a shortcoming in design and actually a far 
> better choice than the SWR rollback and the less robust transistors 
> often used by competing brands. If the amateur had the appropriate 
> matching power supply the worst thing that might happen is the 
> occasional 'popping' of the power supply's power supply breaker.


> It does amaze me how many buy a used Transceiver and either never read 
> the manual, or may not even bother to obtain a manual in the first place 
> and then 'plug-n-play'.... all caution to the wind. Oh well.
> Once again, we are not talking about a design 'shorcoming' but rather a 
> design choice that has served thousands of Ten-Tec customers very well.

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