KK9A wrote: "...if the heat generated is approximately the same with all power levels, why do RTTY ops use lower power..."
First, the heat generated is not actually approximately the same with all power levels. To a first crude approximation, the heat generated is made up of two components. One component is due to such things as biasing for linearity, and is approximately constant whenever the amp is in transmit (it's still non-zero, but quite a bit smaller, when the amp is in standby), and the other component is related to the actual signal being generated, and is approximately linear with output power. At low output powers, the first component dominates, while at higher powers the second component becomes significant. The power consumption efficiency goes from zero at zero power (some mains current being used but generating zero output) to a maximum when the signal-related component is largest compared to the constant component, i.e. at maximum power. Second, what is dissipated is the accumulated heat energy, not power. Heat removal processes are far slower than output power changes, so effectively they integrate the thermal power generation over a significant time interval. If the instantaneous power is the same in two modes, but the duty-cycle factor for one mode is twice the duty factor for the other mode, then the signal-related component of the energy to be dissipated in a given time period will be twice as high for the high-duty mode. The total energy to be dissipated will not be as much as twice as high because of the constant component, but it will still be higher in the higher duty cycle mode. Depending on the thermal design of the amplifier, that may or may not be enough of an increase to require derating. 73, Rich VE3KI ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
