Quote:
Originally Posted by regenfreak
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Quote:
Originally Posted by nemo_07
]o you think you have measured the OPI3 for the MAR-1+ with this little-tiny-weeny toy made in China. And all this in a single step?
You should perhaps look for informations supplied by reliable sites, not by wanna-be experts (remember the "negative group delay"?) like these:
https://tinysa.org/wiki/pmwiki.php?n=Main.OIP3
So they start with "After activating the OIP3 measuring mode ..."
They even didn't bother to realize the meaning of the term "intercept point" (which was explained in the math lessons in elementary school, but they obviously were absent).
So, what their gadget actually does when they talk of "OIP3 measuring mode" is visualizing 3-rd order intermodulation products (measuring their levels and calculating exact locations).
There is laking understanding of some fundamentals. And it is pandemic on the internet these days.
This exposes the simple truth, that the idea of "learning by doing" is fairly incompatible with the very basic principles of electronics (which is in essence the teritory of physics); and any careless and sloppy idea will be rigorously penalized. |
Clearly one of your assumption was that Erik Kaashoek (the creator of the TinySA) and myself are clueless about the definition of the OPI3. I dont care if you call the TinySA a piece of cheap chinese junk, we deserve a public hanging, good beatings or whatever. Whether he is right or wrong, Erik deserves better respect. I thought this is a civilised forum  . Erik should get a pat on his shoulder instead of being bashed and labelled as "wanna-be experts". His TinySA makes RF experiments accessible to students and hobbyists at a very low costs... |
Would I try to call the TinySA a junk or discredit its creator? Certainly not.
I like all these tiny/nano toys and find the ideas standing behind brilliant. We've had yet few words on TinySA
https://www.vintage-radio.net/forum/...1&postcount=69
I did not mean to insult anyone but this text
https://tinysa.org/wiki/pmwiki.php?n=Main.OIP3
as it stands there reads like written by a wanna-be expert, I can't help.
What I actually intended was to point out, that their single-step "OIP3 measurement" is misguided.
Firstly, there is no mention that the basic uncertainty of this feature with the TinySA amounts to +/- 4dB.
Then, there is no warning that the errors of this method are generally not systematic and not predictable, thus turning the "OIP3 measurement" into a Random Number Generation when applied to a DUT with poor linearity.
This (over)simplified method can be safely used with restricted range of device types (some Variable/Programmable Gain Amplifiers, X-Amps, FET devices, vacuum tubes) for which the assumption that the slope of 3-rd order products will be a pretty straight 3dB/dB line is justified.
Taken for granted as general, this assumption is illegitimate, especially in the case of bipolar transistors, where these slopes will most of the time depart more or less from 3dB/dB, depending on bias, drive level and frequency.
In worst case this departure can generate results missed by many, perhaps tens of dB.
Can it be a "learning experience"? Definitely maybe.
Therefore not a quick-and-easy method, but a multipoint measurement with driving levels located around projected bias point with the frequency of interest, and then interpolation would be required to arrive at more or less plausible intercept level.
And then, this tedious procedure will show only one of multitude of possible plots for given device which would be necessary to reveal its true performance.