The advantage I have is that it doesn't set off my fire alarm.
On Thu, 6 Feb 2020, Bob McGraw K4TAX wrote:
I've never seen much if any advantage in running a linear below its
rated output. I know the regulation state never run more power than
needed for adequate communications or terms like that. The difference
between 500 watts and 100 watts is 6.9 dB or about 1 S unit.
In fact, most all of the time, running at less than rated output is less
efficient. It saves nothing. Same for tube amps where I hear hams
say they are running at reduced power to "save the tubes". Nope, not
the case.
(RF output / DC input) * 100 = % efficiency DC input watts = DC
volts x DC amps
Do the math and you'll see what I mean.
A quick run of the numbers with my KPA500 into a dummy load. Output
measured with a Bird 43. DC values taken from the KPA500 display
450 W out, 819 W input, 64 volts @ 12.8 amps for 55% efficiency Drive
pwr = 16.5W 14.3 dB gain 819 - 450 = 369 watts = heating factor = 0.88
210 W out, 576 W input, 67 volts @ 8.6 amps for 37% efficiency Drive pwr
= 7.0 W 14.7 dB gain 576 - 210 = 366 watts = heating factor = 1.74
100 W out, 393 W input, 69 volts @ 5.7 amps for 25% efficiency Drive
pwr = 3.2 W 14.9 dB gain 393 - 100 = 293 watts = heating factor = 2.93
73
Bob, K4TAX
On 2/6/2020 3:07 PM, Rick Bates, NK7I wrote:
Running low output power from it, is far less efficient than pushing
it hard (compare wattages consumed to RF watts output delivered at
different output levels); which may have stressed the finals. Ideally
you run the previous stages at low-moderate power for lower IMD, then
punch it up with the amp.
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