[Elecraft] Does KPA1500 have these KPA500 characteristics?

[Wes Stewart]

Violating guidelines and replying inline.

On 5/25/2018 2:25 PM, Jim Brown wrote:
> On 5/25/2018 1:43 PM, Wes Stewart wrote:
>> I have no idea what you are actually measuring but it certainly isn't IMD in 
>> the classical sense. 
>
> I think I made it plain that I was measuring the "envelope" of keying 
> sidebands, usually described as "clicks." This envelope is due to a 
> combination of the shape of the keying waveform and IMD.

Actually, you said below, "I evaluate IMD blah blah..."
>
> FWIW, I really don't care about IMD as a number. What I'm concerned with is 
> clicks, splatter, and phase noise from another station that's loud covering a 
> weaker station I want to work.

Since the numbers are more-or-less specified by Elecraft I'll go by them.  I say 
more-or-less because they don't actually have a firm specs.
>
>> While it might be "well known" that IMD decreases at lower power, it isn't 
>> necessarily true. 
>
> Right -- it depends on the transmitter design and implementation. K6XX's work 
> shows that to be true of the K3, and my measurements (done on 20M as I recall) 
> confirmed it.  I also recall that you noted increased IMD around 15W, which is 
> likely the result of the K3 firmware causing the power amp to be turned off 
> and the QRP output stage to be driving the load at it's full rated power. 
> Under that condition it is consistent with my (and K6XX's) observations that 
> IMD is often lower at reduced power output.

You recall incorrectly.  First, I've never stated that and second, the HPA 
engages at 12 W.  I have however, stated in strong terms several times in this 
and other forums that a K3 should never be operated above 10W on the LPA.  I and 
others have asked for a firmware change that would insure this.
>
>> What is really not well known is that in the K3(S) IMD is highly frequency 
>> sensitive. 
>
> That's news to me.

Well even experts can learn something new now and again.
>
>> The 3rd order IMD in my K3S at 10W output varies 18 dB with respect to 
>> frequency.
>
> Again, the power amp is not engaged and you're running on the driver. But that 
> much variation also implies a problem. Have you sent the rig back to Elecraft?

Just four times.  (Actually, three times and I changed the HPA once.)
>
>> Furthermore, my K3S on 10, 17, 20, 30 and 40-meters has higher IMD at 20W 
>> than at 100W.
>
> Interesting.

Yep.  Which is why I state that I can't with reasonable confidence measure 
KPA500 IMD.

Wes  N7WS
>
> 73, Jim
>>
>> 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
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