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Author Topic: Why are digi signals rated to 30w on a 120w antenna  (Read 492 times)

Offline Coldwar kid

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Why are digi signals rated to 30w on a 120w antenna
« on: June 11, 2024, 0836 UTC »
On a SSB rated to TX at 120w, from an end feed antenna ?

Offline RobRich

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Tampa, FL USA | US Map Grid EL88
Airspy HF+ Discovery | KiwiSDR 2 | 2x Msi2500 Msi001 | 2x RTL-SDR V3 + NE602 | 2x RTL-SDR V4
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Offline Charlie_Dont_Surf

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Re: Why are digi signals rated to 30w on a 120w antenna
« Reply #2 on: July 04, 2024, 2315 UTC »
https://www.pa9x.com/pep-power-and-duty-cycle-in-amateur-radio :)

While he's not wrong in his basic points, in fact the duty cycle is actually more complicated than his table implies since the duration of an FT8 transmission is always ~12.5 seconds of on time (and FT4 is always ~4.5 seconds) but an AM or FM transmission often is much longer. FM will be "constant envelope" (no amplitude variation), FT8/4 can be close to constant, but AM will necessarily not be constant envelope and power output at 100% modulation will be four times the carrier power, i.e., the power with no modulation.

The overall time scale matters to the heat build up in the PA, baluns, tuners, etc.
I don't STRETCH the truth.

"Every minute I spend in this room, my signal gets weaker.
Every minute Charlie squats in the bush, his signal gets stronger."

 

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