Hi Peter,
you wrote:
> I guess my objection is to taking a technical term that has a definition
> and then simplifying without (as Ian ended up doing) ensuring that the
> simplification and the situation of its applicability is spelled out.
>
> Supposing that for some reason amateurs started using OFDM with M-ary QAM.
> You could well end up on the low bands with the PEP existing for only one
> cycle of RF; this certainly happens at the base band. Thus the definition
> is generally correct, while the application allows latitude. But unless
> one recognises that this latitude is not generally applicable, it easily
> leads to misunderstanding.
That's right Peter. I fully agree.
If you are using a wider bandwidth due to amplitude changing rapidly,
the meter has to be designed to respond to the more rapidly
changing envelope.
> Like bit freaks and 'bandwidth'!
> For all practical purposes, the assumption for amateurs at the moment is
> valid. And the fundamental power measurement as I think it was you that
> said, is the bomb calorimeter. Can you see the sweep tube linears running
> for long enough to reach thermal stability in the calorimeter??
That's why we calibrate the meter against the calorimeter, and then
read the meter.
> Interestingly enough, for purposes of Type Approval, the European
> standards allow a maximum measurement uncertainty to 95% confidence level
> of 1,5dB on conducted RF power, which seems a big tolerance. However, the
> measurement inaccuracy build up justifies this - just because the Bird is
> accurate to 5% of FSD, it doesn't mean that the measurement over all is
> that good.
Be careful with that 5%. While you and I and the rest of the world
think it is true, an expert up in two-land will give you a thrashing for
saying that. I believe he concludes the reading error is 16%, at
least in Electric Ladyland.
73, Tom W8JI
w8ji@contesting.com
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