ORIGINAL MESSAGE:
On Thu, 02 Jul 2009 13:38:08 -0700, Kevin Normoyle <knormoyle@surfnetusa.com>
wrote:
>
>I don't think it's that simple. You can't average over arbitrarily long
>times and say it's 50%. My point was that my macros limit max ON time to
>maybe 7 seconds.
>The max ON time, as well as averages over short and long periods, are
>important for understanding what causes things to melt.
>
>Like I would never do 1 minute ON, even if OFF for the next 3 minutes.
REPLY:
Correct. If you transmit for 24 hours straight and listen for 24 hours straight,
that would not really count as a 50% duty cycle, would it? :-)
No doubt the IEEE has a more scientific definition, but I would say you have
reached the limit when all parts inside the box reach a maximum temp and
stabilize there. At that point you are effectively at 100% duty cycle,
regardless of how much longer you continue to transmit.
At a lower duty cycle, you would not reach that max temp, and it shouldn't
matter whether it was one second on, one second off or ten seconds on, ten off
and so on. Either way would be 50% and the box should stabilize at the same
average temp. I say "average" because the longer period would have more "ripple"
on the temp graph. How much "ripple" depends mainly on the physical mass of the
parts in the box, but whether the "ripple" is significant depends entirely on
the particular design and susceptibility of individual parts to heat damage.
Electronics can be as much art as science.
73, Bill W6WRT
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