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.
"snip"
> 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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