[Elecraft] Upper limits of KPA500?

[Dave Cole]

Hi Rick,

This brings up a point I have been unsure about for years...  Duty 
Cycle...  What constitutes 100%?  Over how long a time frame?

If I run JT65, (one minute on one minute off), and I use a timeframe of 
say 5 minutes, I buy it is 50% duty cycle.

But if I use a timeframe of one minute it is 100% Duty Cycle...

So when stating duty cycle it is important to spec the timeframe, as you 
did...  Is there an actual timeframe stated someplace as a standard?

I do like the way you stated it by the way...  With time to 'catch the 
breath'...

73, and thanks,
Dave (NK7Z)
https://www.nk7z.net
ARRL Volunteer Examiner
ARRL Technical Specialist
ARRL Asst. Director, NW Division, Technical Resources

On 5/3/20 8:53 PM, Rick Bates, NK7I wrote:
> I didn't add the obvious, FT8 in that manner is a 50% duty cycle but 
> with enough time to 'catch the breath'.
> 
> I remember back when it first came out, Wayne suggested to 'run it with 
> all the LEDs lit' or something along that line but... it's capable of 
> MUCH more than 500 watts and wisely better limited by firmware upgrades 
> (in the early days I watched it put out almost 700, at which point I was 
> far more cautious).  It's nice to know there is a certain amount of 
> 'overhead'.
> 
> Rick NK7I
> 
> 
> On 5/3/2020 8:23 PM, Dave Cole wrote:
>> Hi Rick,
>> That is how mine behaves as well, almost exactly like that... However, 
>> I will be running SSTV, and that is hard on the amp...  I need to do a 
>> bit more testing prior to that.
>>
>> As someone else said upthread, half power is really tough on the amp...
>>
>> 73, and thanks,
>> Dave (NK7Z)
>> https://www.nk7z.net
>> ARRL Volunteer Examiner
>> ARRL Technical Specialist
>> ARRL Asst. Director, NW Division, Technical Resources
>>
>> On 5/3/20 7:52 PM, Rick Bates, NK7I wrote:
>>> I spent 15 minutes active on 20M FT8 this afternoon (some lurking).
>>>
>>> At 530 watts output (on the display and utility) into a 1.13:1 
>>> antenna load (SteppIR) for a ten minute calling period (Mongolia then 
>>> Oman), the temp rose to 66C; a few moments of elevated fan quickly 
>>> brought that down to the low 60's between transmissions.
>>>
>>> Ambient room temp 77F.  (Both calls succeeded.)
>>>
>>> Rick NK7I
>>> North Idaho
>>>
>>> On 5/3/2020 7:42 PM, Andy Durbin wrote:
>>>> "It is interesting to hear how others experience their KPA500s over 
>>>> various conditions."
>>>>
>>>> I have over a years's worth of KPA500 data recorded but it takes 
>>>> some effort to run it through the Excel templates to make pretty plots.
>>>>
>>>> My KPA500 temperatures are strongly influenced by ambient 
>>>> temperature.  Shack temperature is often over 30 deg C in the summer 
>>>> months and it's not at all unusual for my fan to run at level 3 in 
>>>> FT8 QSO.  I think I have only reached fan speed 5 twice and that was 
>>>> while running temperature tests not while operating.   I terminated 
>>>> those tests at fan speed 5 and didn't wish to push it any higher.
>>>>
>>>> So many people seem to think reducing the output power will keep the 
>>>> temperature down.  It does not.   Half power is about the worst heat 
>>>> dissipation condition for the KPA500.
>>>>
>>>> 73,
>>>> Andy, k3wyc
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