liquid paper, liquid wrench, and now...

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sofaspud
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liquid paper, liquid wrench, and now...

Post by sofaspud » Fri Dec 18, 2009 6:32 pm

liquid antennas
An interesting new technology, one I can envision having ubiquitous applications. There's
already N&V-type stuff from the ham radio bunch. It's worth a look.

denkiguy
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Re: liquid paper, liquid wrench, and now...

Post by denkiguy » Fri Dec 18, 2009 9:06 pm

The article mentions the possible use of a liquid antenna as an ultra sensitive strain guage. I assume the idea is that the strain on a bridge support can be inferred from the change of length of one of these stretchy antennas. Where in the world do they get the figure 0.3 percent accuracy and what does it mean? Is the claim that a change in mechanical strain can be measured remotely with an accuracy of 0.3 percent? I wonder how accurately the actual antenna length can be measured? It sounds like there would be RFID applications also.

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Bob Scott
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Re: liquid paper, liquid wrench, and now...

Post by Bob Scott » Sat Dec 19, 2009 10:31 am

denkiguy wrote:Where in the world do they get the figure 0.3 percent accuracy and what does it mean?
I noticed that too. I guess it means that it's 99.7% inaccurate or that the author made mistakes. I think those ads are just filled with speculation and the rag is not a stickler for accuracy.

Think about ham antennas and how the skin effect of tiny wire would make it highly resistive. I think that this stuff would make a poor antenna if made skinny.

:idea: That's odd: Skinny people have less skin. I wonder why our ancestors came to call them skinny. (?)
-=VA7KOR=- My solar system includes Pluto.

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reloadron
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Re: liquid paper, liquid wrench, and now...

Post by reloadron » Sat Dec 19, 2009 10:44 am

I never got that entire accuracy thing :???: To me accuracy is a qualitative term and not generally expressed in numbers. Error on the other hand is a quantitative term generally expressed as a numeric value. If someone tells me the accuracy of something is for example +/- 0.3% then I see the allowable error as +/- 99.7% or not something I want to rely on. Accuracy is unbiased precision, we can't have accuracy without having precision. The error of 99.7% exactly as Bob states it.

I would state the above as the error (or uncertainty) is not to exceed +/- 0.3% so beats the heck out of me.

<EDIT> Edited my text to read "Accuracy is unbiased precision, we can't have accuracy without precision". </EDIT>

Ron

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Re: liquid paper, liquid wrench, and now...

Post by KC8LWW » Sat Dec 19, 2009 11:43 am

Like most specifications, accuracy means nothing without a range. Antennas are spec'ed for gain in dB(d) against the gain of a perfect dipole at the same frequency. If you had a ham radio 2 meter antenna (144-148 MHz) and the gain was stated as 10dB(d) with 0.03% accuracy, then the gain could vary from 9.97 dB to 10.03 dB.

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reloadron
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Re: liquid paper, liquid wrench, and now...

Post by reloadron » Sat Dec 19, 2009 4:21 pm

KC8LWW wrote:Like most specifications, accuracy means nothing without a range. Antennas are spec'ed for gain in dB(d) against the gain of a perfect dipole at the same frequency. If you had a ham radio 2 meter antenna (144-148 MHz) and the gain was stated as 10dB(d) with 0.03% accuracy, then the gain could vary from 9.97 dB to 10.03 dB.
Yes, but would that be the best way to state it, using the word accuracy? Would it be better stated if we said the antenna has a gain of 10dB with an error not to exceed +/- .03 dB? Just seems if someone states an accuracy of for example +/- .03% with a range of 10 and the accuracy is a percentage of Full Scale then the inaccuracy is 99.97%.

Ron

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Re: liquid paper, liquid wrench, and now...

Post by CeaSaR » Sat Dec 19, 2009 5:47 pm

The definition of accuracy is the ability to hit a target, whether it be physical or mathematical.
Precision is defined as the degree of repeatability. So, if an archer can place an arrow in the center
of the target when aimed as such, then he is accurate. If the archer shoots to the left 2" consistently,
then he is precise, but not accurate. If, in the first case, he consistently puts the arrow in the center,
then he is BOTH accurate and precise.

This explanation comes from my son's teacher earlier this year when she taught precision and accuracy
in relation to science. I believe it is a very apt analogy.

Hope it helps,

CeaSaR
Hey, what do I know?

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Re: liquid paper, liquid wrench, and now...

Post by KC8LWW » Sat Dec 19, 2009 8:41 pm

Then using CeaSar's analogy, if my example antenna exibited a gain within the range 9.97 dB and 10.03 dB consistently, it is said to be within the specified accuracy, or within specification. If it consistently measured 9.5 dB, then it is precise, but not accurate. We say it is out of specification.

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Re: liquid paper, liquid wrench, and now...

Post by reloadron » Sun Dec 20, 2009 3:17 am

KC8LWW wrote:Then using CeaSar's analogy, if my example antenna exibited a gain within the range 9.97 dB and 10.03 dB consistently, it is said to be within the specified accuracy, or within specification. If it consistently measured 9.5 dB, then it is precise, but not accurate. We say it is out of specification.
That's how I see it. Out of specification or out of tolerance as the deviation from nominal exceeds the stated allowable uncertainty.

Ron

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Re: liquid paper, liquid wrench, and now...

Post by jwax » Sun Dec 20, 2009 2:38 pm

My math says 10 db +/- 0.03% = 9.997-10.003 db.

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reloadron
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Re: liquid paper, liquid wrench, and now...

Post by reloadron » Sun Dec 20, 2009 3:17 pm

Uh Oh, :smile:

Following advanced calculations...

.0003 x 10 = .003

I do believe jwax has a point there.

Ron

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