[Elecraft] Upper limits of KPA500?

Mon May 4 14:11:00 EDT 2020

Hi John,

Pretty much every answer to the Duty Cycle question involved time, hence 
why I asked about RTTY, that forced the issue of time to come into the 
definition.

Based on the manual definition, 10 minutes out of every 15 can be in 
transmit.  That seems to constitute 100% duty cycle for the KPA500.  So 
I now have my question answered.

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

On 5/4/20 6:53 AM, John Simmons wrote:
> Nowadays manufacturers use 'ICAS'. One even specs their amp for '100% 
> duty cycle ICAS'. ICAS=Intermittent Continuous Amateur Service'. 
> Gobbledegook!
> 
> 100% duty cycle is what Alpha used to say.... brick on the key forever. 
> FT8, JT65 are 50% duty cycle modes. SSB is about 33% during transmit, CW 
> is 50% during transmit. Duty cycle has no time limit.
> 
> -de John NI0K
> 
> Dave Cole wrote on 5/4/2020 8:39 AM:
>> 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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> 
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