Dave,
Probably one of the best VNAs for the money?is the SDR-Kits?VNWA 3SE Automatic 2 Port VNA - N-Connector Version. I own 2 of them and use one almost every day. They have great support and there is a good groups.io group that are very helpful.?
On Saturday, October 5, 2024, 5:49 PM, W0LEV <davearea51a@...> wrote:
Since I and many others are totally unaware of the origins or derivation of that "formula", I believe the best path forward is to start over.? Is anyone aware of the origin or derivation of it?? Forget the undocumented "formula" which may be just a sloppy curve fit to some questionable data.? I don't know.? But let's make measurements and keep the lines of communications and analysis open to our measurements even if our conclusions are based on empirically derived data.? Personally, I digested and put a lot of faith in the recent EZNEC analysis.? Thank your for that effort!? I've used EZNEC and 4NEC2 for some 3 decades.? My physics background forbids me from accepting random "formulas" without a derivation of good fit to empirically derived and properly measured and presented data.? Remember, statistics can render data to imply anything the statistician requires.? Even with good data.......? I've seen it too many times in my career! ? Take arguments for/against global warming and/or analysis of the Colorado River water flow (I live in N. Colorado).
What does the denominator in that formula represent with:? c x L?? Does basic unit analysis prove it's "real"?? In my physics and EE classes, many times the prof would stress unit analysis to indicate things "might" be correct.??
I believe one extremely useful instrument in this respect would be one of the NANOVNAs (they're cost is considerably less [no recent Chinese entries, please - I have three] than an amateur radio HT).? And, of course, the knowledge of how to properly use them - not a simple and short learning curve.? I've been using "professional" VNAs for some 40-years - the expensive ones.? The present offerings give those a real run for their money!!? Believe me, I have the HP 8753C with the S-parameter test set and have done comparisons.? If I were one of the "big boys" I would be embarrassed to offer them at the prices they do.? Of course, they laugh all the way to the bank.? Enough of a "pep talk" on the usefulness of the VNAs.? I can make some proposed measurements if needed and contribute to the group.
Also, the TINYSAs enable us to make quantitative measurements of currents, voltages in free space with known "antennas" and probes.? Again, today they cost less than the previously referred to amateur HTs.? And....the same quality arguments apply.??
Maybe it's time we get "down and dirty", abandon the undocumented formula, and make our own measurements.
This got MUCH longer than I initially intended.
Dave - W?LEV ? ??
On Sat, Oct 5, 2024 at 5:27?PM Raphael Wasserman via <wassermanr46=
[email protected]> wrote:
Hi Chavdar,
?
What bothers me in your published article signals-mag_loop_engl.htm where using known equations you concluded in the? short current mode the induced current in the loop is independant from frequency, using the proposed equivalent model of SML:
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?I = w x S x u / c x L , where w - number of loop turns, S - square area of loop, u - magnetic constant, c -velocity of light and L - loop inductance.
?
Also, this postulate does not suit with your "dummy" aerial model? with a parallel LCR circuit across amplifier input? because it is frequency dependant.
Let's for a sake of argument? forget about the mathematical description of small loop antenna behaviour.
We have a metallic loop where a magnetical filed induces current and that loop has distributed ohmic resistance and inductance. Across loop terminal points we connect a 3 ohms resistive load ( for short current mode ) to close this loop. Only when the reactive element? in series, namely the inductance, is significantly less than the ohmic resistance of the loop I suppose we can say we have a flat independant frequency response of antenna.
The frequency rises so the reactive resistance of loop antenna and the current through the load diminishes.
Now let's go back to test circuit ( dummy aerial layout ) proposed by you:
1. Where is there the current Norton's source ?
2. For lower frequencies the parallel circuit shall? shunt away more current from the 3 ohms load than for higher frequencies ( less applied signal to the amplifier ).
? ? In reality the AF for SMA is greater at lower frequencies than at higher frequencies ( more signal is applied to the amplifier ).
Your detailed response is appreciated.
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Regards,
?
Raphael
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Everett N4CY