[Elecraft] KPA500 Power In Digital Modes

[Joe Subich, W4TV]

> Joe made this statement assuming that the KPA500 produced FAR more
> distortion than it actually does. A few days later, I showed
> measurements with a K3 driving a KPA500 to 500W with PSK31 showing
> that the distortion was EXTREMELY low.

Jim, is misconstruing what I wrote.  I specifically said "*average*
power from the KPA-500 should be kept 6-10 dB below the maximum".
Jim made his measurements at PEP which *includes* the crest factor
(PEP = average power X Crest factor or alternately Average Power =
PEP/Crest Factor).  If his measurements were made at average power,
the results would have been considerably different.

With most PSK, MFSK, PACTOR, etc. modes, it is important that the
average power output be kept low enough that none of the amplifier
stages is driven into saturation on the peaks which can be anywhere
from 3 dB to 13 dB greater than average depending on the digital
modulation.   Note: FSK, JT65 and JT9 modes are "saturated" - their
crest factor is 1 (0 dB).  Like CW, for those modes, PEP = average
power.

73,

    ... Joe, W4TV


On 2014-11-19 11:49 AM, Jim Brown wrote:
> On Wed,11/19/2014 3:50 AM, Ken wrote:
>> On Nov 10, 2014, at 7:30 PM, Joe Subich, W4TV wrote:
>>
>>> >Depending on the crest factor (peak to average ratio) of the mode
>>> >in use, the average power from the KPA-5000 should be kept 6 to 10
>>> >dB below the rated maximum (e.g., 60 to 150 watts) just as a 100W
>>> >transceiver should be kept between 10 and 25 watts average.
>
> Joe made this statement assuming that the KPA500 produced FAR more
> distortion than it actually does. A few days later, I showed
> measurements with a K3 driving a KPA500 to 500W with PSK31 showing that
> the distortion was EXTREMELY low. I had already published comparable
> measurements for CW and SSB, with the same result.
>
> P3SpectrumMeasurementsSlides.pdf
>
> 73, Jim K9YC
>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Elecraft at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to lists at subich.com
>