I frequently wonder just how much protection a typical SWR protection circuit can provide against an instantaneous discontinuity if it relies totally on a feedback approach. If the response time of the feedback circuit isn’t faster than the risetime of the voltage at the output transistors that results from a sudden failure, then it isn’t apparent to me how this approach can provide reliable protection. A well-designed feedback circuit can provide adequate protection during tune up into a high SWR. It can also provide adequate protection during CW or voice modulation since the bandwidth, and therefore the risetime, of the transmitted signal is limited by the transmitter circuitry. However, the voltage rise due to a sudden failure in an antenna or transmission line connection could conceivably result in a risetime in the 100 nsec range at the drains/collectors of the output transistors. I have never seen any specs on the response time of any SWR protection circuit, but I would be surprised if any of them can even approach the low nsec range. If the failure occurs when the transmitter is at full output, then I would expect the voltage to quickly exceed the max rating on the output transistors. This is clearly a worst-case scenario that probably doesn’t occur very often. However, I wonder how many (if any) manufacturers of ham transmitters have disconnected the antenna when their transmitter was putting out full power as part of their evaluation of their SWR protection circuit.
Bill N0CU -- View this message in context: http://elecraft.365791.n2.nabble.com/New-K3-K3S-Beta-Firmware-rev-5-57-Faster-response-to-high-reflected-power-tp7627082p7627122.html Sent from the Elecraft mailing list archive at Nabble.com. ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [email protected]
