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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