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General Category => General Radio Discussion => Topic started by: JACE26 on June 11, 2024, 0836 UTC

Title: Why are digi signals rated to 30w on a 120w antenna
Post by: JACE26 on June 11, 2024, 0836 UTC
On a SSB rated to TX at 120w, from an end feed antenna ?
Title: Re: Why are digi signals rated to 30w on a 120w antenna
Post by: RobRich on June 11, 2024, 1430 UTC
https://www.pa9x.com/pep-power-and-duty-cycle-in-amateur-radio :)
Title: Re: Why are digi signals rated to 30w on a 120w antenna
Post by: Charlie_Dont_Surf on July 04, 2024, 2315 UTC
Quote from: RobRich on June 11, 2024, 1430 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.