[Elecraft] Does KPA1500 have these KPA500 characteristics?

[Wes Stewart]

I have no idea what you are actually measuring but it certainly isn't IMD in the 
classical sense. While it might be "well known" that IMD decreases at lower 
power, it isn't necessarily true.  What is really not well known is that in the 
K3(S) IMD is highly frequency sensitive.  The 3rd order IMD in my K3S at 10W 
output varies 18 dB with respect to frequency.

Furthermore, my K3S on 10, 17, 20, 30 and 40-meters has higher IMD at 20W than 
at 100W.

Wes  N7WS

On 5/24/2018 8:17 PM, Jim Brown wrote:
> On 5/24/2018 7:30 PM, Wes Stewart wrote:
>> I haven't measured IMD on my KPA500 either since I don't own two generators 
>> that are clean enough with the necessary power to do so. 
>
> I evaluate IMD by looking at keying sidebands of a long series of dits, as I 
> posted hear yesterday. Details of the measurement setup and  method, and lots 
> of results, are here. http://k9yc.com/P3_Spectrum_Measurements.pdf
>
> It's well known that IMD in the K3/K3S increases at rated output, and is a lot 
> lower at the levels needed to drive a power amp. It takes 25-30W to drive the 
> KPA500 to full power, and about twice that to drive my Ten Tec Titans. The 
> K3/K3S is pretty clean at these levels. The plots for the two amps look almost 
> exactly the same, and have the same shape as the K3 at those drive levels.In 
> other words, neither amp is increasing bandwidth. Note that these measurements 
> are of the envelope of peaks, so they are, in essence, capturing clicks.
>
> IMD also increases with low DC supply voltage. I've not done any disciplined 
> measurements to put numbers to it, but K6XX has. His data is in this pdf slide 
> show. http://k9yc.com/K6XXAmpTalk.pdf
>
> 73, Jim K9YC