[Elecraft] Duty Cycle of FT8 #Elecraft

[Rick NK7I]

The duty cycle of FTx is 43.3% and may be less than RTTY or PSK 
depending on the transmit:receive ratio; or long winded SSB.

I've run the KPA1500 at or near legal limit into a resonant antenna on 
Ftx, for hours at a time without issues.  It will warm the shack and I 
suggest headphones, the fan can make some noise.

The lower output that you run, the less efficient the amp is, which is 
total power used (presented as heat) to output power. Sometimes (30M), 
that's the cost (the K3/4 won't produce the US legal limit of 200 watts, 
without the amp).

73,
Rick nk7i


On 11/10/2023 11:14 AM, Victor Rosenthal wrote:
> I don't have a kpa1500, but I recall someone from Elecraft saying that
> since the efficiency decreases when power is reduced, backing off the power
> does not reduce the heat load.
>
> Victor 4X6GP
>
> On Fri, Nov 10, 2023, 16:28 Pete Smith N4ZR <pete.n4zr at gmail.com> wrote:
>
>> I started operating FT8 while my KPA-1500amp was out for repair.  Now
>> it's back and raising a question:
>>
>> Operating with just my K-3, set at 100 watts, I would see 100 watts
>> indicated on its meter through the whole 15-second FT8 transmission..
>> When I drive my amp, it only needs 30 watts for full CW power (on 24
>> MHz),  but the amp indicates 1200 watts input for the whole FT8 transmit
>> cycle.  I'm wondering if I should back off to protect the
>> amp,considering the duty cycle is so high - on the other hand, the
>> temperature reading profile of the amp seems to be pretty much the same
>> as on CW.
>>
>> 73, Pete N4ZR
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