locked Re: Duty cycle question


And I might add, What power level you can run is 100% determined by how well you can get rid of this heat being generated.

Example. My Kenwood TS-430S

I can run FT-8, RTTY, etc. at full output ~110 watts.

At full output ~110 watts after about 10 minutes of operating the heat sink fan turns on.
And unless I stop transmitting it never turns off.  So I am assuming I am making more heat than the system can remove.

at 90 to 95 watts, I can operate about 15 minutes and then the fan turns on,  it runs for about 5 minutes then shuts off. Then about 5 minutes later it turns on again, and so on repeating the on off cycle.  So at that power level I can remove the heat generated, but the heat sink alone is not enough it needs some help from the fan.

at 80 watts or lower,  The heat sink alone is enough the fan never ever turns on.


The Original Rolling Ball Clock
Idle Tyme

On 8/16/2020 10:08 AM, Kai-KE4PT wrote:

It's not a yes /no question. It depends on the measurement duration.
FT8 is 100% duty FACTOR: when transmitter is ON, Paverage = PEP; this is the same as for FM voice, and RTTY. and carrier key-down.
FT8 is also has a duty CYCLE: this is the percentage of time that the transmitter is ON over a TX/RX cycle; (how long is the cycle of transmission durations and reception durations do you care about, and how much OFF time between cycles do you want to include?)

By comparison, SSB voice (no processing) duty FACTOR is about 20%, and its duty CYCLE is the percentage of time transmitting (lets say 50% of time TX, 50% RX for a chatty QSO), then SSB duty factor for that scenario is 50%. The average power of that scenario is 0.20 X 0.50 X PEP = 10% of PEP over the TX+RX duration.

You have to multiply (duty factor) X (duty cycle) X (transmitter PEP) to get the average power over the time cycle you care about - one that affects the transmitter thermal safety parameters. How long can you safely key the TX at full power (100% duty factor)?

The practical answer for FT8 might well be:
If the thermal problem occurs in just a few seconds of transmitter ON time, then duty cycle is irrelevant, and the prudent thing is to use the FT8 duty factor alone, which like RTTY and FMvoice is 100%, but for SSB voice is 20%).

Kai, KE4PT

On 8/16/2020 10:10, John G0GCD wrote:
Is FT8 100% duty cycle? Yes, no and possibly. It depends on the definition of duty cycle you mean

John G0GCD


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