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Steve ugly-build LZ1AQ using MPS2222 sweeps uploaded to Photos
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I linked the Duffy article in post#19752. The section at the end of that article is sub-titled "Diodes connected to antennas"
73, Chin-Leong Lim, 9W2LC
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Hi Martin,
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Well when you have a separate 50 ohms coupling loop ( your excitation loop ) coupled with a tuned loop:?
1. More separation betveen both loops - lower the magnetic coupling K coefficient, less induced power from excitation loop into the tuned loop.
2. Less separation, the coupling coefficient rises, induced power goes up and the resonant frequency of tuned loop goes up insignificantly in accordance with:? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? f= 1/2xpi x sqrt (( La (1-K^2)x Ca)) .
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Raphael
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I think the principle is good.
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It may be easier to place the transmission line balun on the 50 ohm side of the simulator.
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I suspect the divergence of the results above 20MHz may be associated with the balun.
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Do the results change significantly if the balun is omitted or changed in some other way ?
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I'll build up your circuit and perform some experiments.
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Incidentally, I'm surprised the MLA-30 produced that curve, since I examined one, I think they must have made some improvements to the design.
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Good work,
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Martin
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On Sat, Sep 28, 2024 at 09:21 AM, <biastee@...> wrote:
I have recorded the details of my dummy aerial in .? I will be grateful if you can critique it. Thanks. |
I have considered that, but gave up because the L-network would have to be a balanced / symmetrical? like the one described by Wasserman in reply #19710 & 19720; i.e. two inductors would be required instead of one.
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Are you referring to the table in fig. 9? If yes, the "measured" refers to your data, while "model" is the dummy aerial's simulated impedance. In other words, there is no measured data of the dummy aerial (my laziness shows!).
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It's good that you asked this question because it makes me realize that there is a need to present the information more clearly. Would renaming the aforementioned as "loop - measured" and "dummy - modelled" be a better alternative (see changed table below)? Previously, I didn't want to be verbose because it will increase the top table's row height.
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It's MLA-30+.
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Martin, Thanks for the useful feedback.
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73, Chin-leong Lim, 9W2LC
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Placing the transmission line transformer on the input or output makes no difference to the balance. All it does is act as a common mode choke. However on the input side the differential mode impedance is fixed at 50 ohms. On the output side it varies, and contributes to the impedance curve.
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The other issue is the low value of coupling capacitance (in a 50 ohm path) at the low frequency end of the frequency range. The amplifier measurements show this clearly, with a rapid decrease in ?S21. Real loops don't behave in this way.
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I still think an air wound inductor, brought to resonance with a parallel capacitor, and loaded to present the correct coupling and overall Q, by means of a closely coupled overwinding, provides a more accurate impedance curve and S21 plot, plus it is already pretty well balanced, but an extra choke balun, on the 50 ohm side, could help at the higher frequencies.
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The amount of coupling will "tame" the impedance excursion near resonance, so that is more like a actual loop. If not a parallel resistor could be added, to simulate other losses, such as radiation.
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Just my thoughts...
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Regards,
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Martin
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开云体育Hi Chin-leong Lim and All, ? I reviewed your article. What bothers me your conclusion about the equivalent ?circuitry of untuned unshielded small loop antenna and the proposed schematic diagram of dummy aerial to test it with an antenna amplifier. First, let's look at the taken graph of scattered parameter S11 of loop antenna where the impedance is shown as a value (R + jX). ???????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????We have at about 30 MHz a parallel circuit resonance not a series circuit resonance. Then your Thevenin representation of loop antenna as L – shaped circuit, where the series arm is inductive and shunt arm is capacitive will contradict an essence of parallel resonance ?but it will applicable to series circuit resonance nature. The trick is here, if you would represent it as Norton equivalent circuit then it is fine. However, for Norton circuit you would need to have physically a current source not a voltage source ! In our practice ?we use a frequency generator as a voltage source, so the dummy antenna equivalency circuit shall be built accordingly ?for the used voltage source. In my opinion, the dummy aerial for a balanced untuned small loop antenna shall consist of two series arms with ?connected in parallel elements 1/2 La and 2Ca and shunt arm Ra. You were right in my correspondence with this site I proposed to use a dummy antenna fixture for small loop antennae but I did not published a specific layout of it for our community. The reason for that ?there is no strict standards for design small loop antennae. There will be a great variation of La and Ca parameters ( when dummy antenna was proposed in last century for radio receivers in mind was a single couple meters long a wire antenna and later another dummy antenna for testing car radios ). For my individual usage I constructed one and successfully used it since then. Also, that suggested representation of dummy aerial will not contradict with Owen Duffy's concept of calculation SND for different input impedances of antenna amplifiers including antenna inductance for optimum match as (2 x pi x Fo x La / R input) to obtain an optimal power transmission from antenna to antenna amplifier. He uses La in series arm of his "Voltage Divider", where R input is in shunt arm. ? Regards, ? Raphael ? ? From: [email protected] <[email protected]> On Behalf Of biastee via groups.io
Sent: Saturday, September 28, 2024 5:21 AM To: [email protected] Subject: Re: [loopantennas] Steve ugly-build LZ1AQ using MPS2222 sweeps uploaded to Photos ?
Hi all, I have recorded the details of my dummy aerial in .? I will be grateful if you can critique it. Thanks. ? 73, Chin-leong Lim, 9W2LC |
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Hi Raphael,
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I agree there are no strict standards, but most broadband active loops tend to use a loop diameter of approx 1m, an inductance of 2.5uH and a self resonance just above 30MHz.
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I think that is good enough for comparative purposes on the bench, and it complements a purely restive measurement of S11 and S21 when applied to practical loop amplifiers.
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Something is better than nothing, “Strive for progress, not perfection.”
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This is my best attempt. A simple inductor with the same inductance as that of an actual typical 1m loop, at around 2.5uH. Brought to resonance at just above 30MHz, with a parallel connected capacitor. The coupling factor between the inductor and a few turns of wire providing an overwind, for connection to a 50 ohm signal source. The coupling can be varied, in order to achieve an impedance comparable to that of an actual loop at the resonant frequency.
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/g/loopantennas/photo/267767/3835135
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Comparison of the simulator vs. actual loop impedances.
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Does anyone have any counterproposals of another practical circuit that can be evaluated ?
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Regards,
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Martin
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On Sat, Sep 28, 2024 at 04:27 PM, Raphael Wasserman wrote:
he reason for that ?there is no strict standards for design small loop antennae |
开云体育Hi Martin, ? In my profession I always strived for perfection especially when someone wants to publish his work in a magazine by any means… Please take another look of Chin-leong Lim's article where he recommends a certain layout of dummy antenna equivalency for a small loop antenna: ?
He used two models: ?
? Regards, ? Raphael ? From: [email protected] <[email protected]> On Behalf Of Martin - Southwest UK via groups.io
Sent: Saturday, September 28, 2024 4:57 PM To: [email protected] Subject: Re: [loopantennas] Steve ugly-build LZ1AQ using MPS2222 sweeps uploaded to Photos ? Hi Raphael, ? I agree there are no strict standards, but most broadband active loops tend to use a loop diameter of approx 1m, an inductance of 2.5uH and a self resonance just above 30MHz. ? I think that is good enough for comparative purposes on the bench, and it complements a purely restive measurement of S11 and S21 when applied to practical loop amplifiers. ? Something is better than nothing, “Strive for progress, not perfection.” ? This is my best attempt. A simple inductor with the same inductance as that of an actual typical 1m loop, at around 2.5uH. Brought to resonance at just above 30MHz, with a parallel connected capacitor. The coupling factor between the inductor and a few turns of wire providing an overwind, for connection to a 50 ohm signal source. The coupling can be varied, in order to achieve an impedance comparable to that of an actual loop at the resonant frequency. ? ? Comparison of the simulator vs. actual loop impedances. ? ? Does anyone have any counterproposals of another practical circuit that can be evaluated ? ? Regards, ? Martin ? ? On Sat, Sep 28, 2024 at 04:27 PM, Raphael Wasserman wrote:
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On Sat, Sep 28, 2024 at 09:27 AM, Raphael Wasserman wrote:
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Hi Raphael,
Thanks for pointing out flaws that I have overlooked due to writer's tunnel vision. I know reviewing is very time consuming and so thank you from the bottom of my heart for the detailed review.?
There is a Guanella balun at the output of the proposed dummy aerial (L2 in fig. 5). Can that address your concerns?
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In case that balun doesn't fully address your concerns, there is still opportunity for a version 2 (V2) of the dummy that incorporates your recommended balanced L network with 2 series inductors. :-) And V3, V4 and so on... However, the current V1 is still useful because it has generated a set of baseline data that V2 can improve upon. The reason for V1 using the unbalanced L network (1 series inductor) is convenience. For completeness, I plan to revise the article to include a short discussion of your recommended balanced L network.?
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To Ehrenfest (I can't resist that :-)) Ehrenfried's? exhortation, I would like to add that imprecise or imperfect data can be useful to the scientific community.
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"The fact that Aristarchus and Huygens used imprecise data and derived imperfect answers hardly matters. They explained their methods so clearly that, when better observations were available, more accurate answers could be derived." - Carl Sagan, Cosmos, ch. 7.
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In the messy business of experimental work, a succession of progressively less imprecise results may be required before convergence at the correct final answer (see history of electron charge in graph below).
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The usefulness of imprecise results notwithstanding, it is important for reviewers to keep pointing out the flaws so that lab-rats can devise successively better experiments.?
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73, Chin-leong Lim, 9W2LC
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Hi Raphael,
Apologies in advance, as I once again embrace the role of “philosophical sage”. <sage> It’s basically the very old “Academia vs. Industry” debate. A lot depends upon the context, and in some instances accuracy and excellence are vital, in others much less so. We also need to distinguish between Excellence and Perfection. Chin-leong Lim’s example of the derivation of electron charge is a good one. Do you wait 50 years (1910-1960) for an accurate, stable, value to be obtained, or do you work with what you have got at any moment in time ?? Interestingly, an iterative process obtained the result, and this is the basis of the Agile methodology, in widespread use by software developers. It attempts to bridge the gap between excellence, and actually having something to sell. There are a number of key takeaways in the list of 12 Principles, some of which you may agree with, and others you may not. In phycology, there is a strong link between Perfectionism & Procrastination. My wife trained in phycology, and she taught me the mantra “Good is Good enough”. If you have certain traits, and most engineers, myself included, do, then we tend to be somewhere on the autistic spectrum. Embracing “Good is Good enough” can be empowering, free up a lot of your time, and reduce levels of stress and anxiety. ? That’s not to say you shouldn’t strive for excellence, but you need to temper it to suit the situation, otherwise the search for perfection can become a lifelong quest, with no actual outcome at the end. Especially for Chin-leong Lim. Here are some more “Ehrenfried's ?exhortation’s”, I genuinely wish I could say I originated them, but a quick search of the internet will reveal their true source. “Perfect is the enemy of good” “Better to do something imperfectly than to do nothing perfectly” “If you look for perfection, you’ll never be content” “Striving for excellence motivates you; striving for perfection is demoralizing” I’m currently reading a translation of The Tao Te Ching, so maybe my viewpoint will shift, once I fully embrace the Tao, but I suspect that will be another lifelong quest… </sage> My point is, let’s have something practical, as a starting point to build on, and then contribute alternatives or enhancements along the way. ?This means, in addition to theoretical designs, we need circuits we can build and test. ?
"Something is better than nothing"
Regards, Martin ?
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On Sat, Sep 28, 2024 at 11:11 PM, Raphael Wasserman wrote:
In my profession I always strived for perfection especially when someone wants to publish his work in a magazine by any means |
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Chin-leong LIm,
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A presence of writer's tunnel vision ? C'mon, don't be silly with that! You made my morning for a good laughing that positively effects the health. There I am on same page with Martin...
In order to design or propose a dummy antenna device, especially for small active antennae, I consider the antenna and its apmplifier should be as one integrated unit, where any elements between them shall not be altered ( that impedes comparison process between various SMA designs ). For example, if there exist balun, equilizer or filter they will stay unaltered ( not requiring additional elements ).?
If you experience issue of connection an unbalanced output of your VNA to balanced dummy antenna device input, worry about that connection correction exactly between these mentioned ports.
Your suggested dummy equivalent circuitry for SMA is wrong - the series element leg shall be inductance and shunt leg capacitor. In your design it is reversed.
There are some other shortcuts but I will allow you to find them on own.
In some extent it reminds me a story when I bought inexpensive chineese made SDR finding later that front end of preselectors perform funny. I discovered issues with their design - blindly copying western design and deciding to make a quick buck selling world wide. So, I redid that SDR. Later the owner of chineese outfit ask me to mail him all made corrections. I refused that because I do not like an idea of? stealing technical patents for profiting later. Anyone can reverse engineer some electronic devices but it should stay with that person.
Since you have been designed wrongly the dummy aerial, subsequentially all? your published graphs of frequency responses for a number of mentioned SMA shall be rerun as well.
Take a minute to suppress somehow your writer's tunnel vision. Your presentation of dummy antenna is a simplistic high pass filter with one section where the cutoff frequency is about the frequency of first parallel resonance of SMA. So, your frequency graphs should show attenuation between 0 and F0 ( resonance frequency ).
In actuality, the dummy antenna shall represent a low pass filter with same cutoff resonance frequency ( when it is used? as Thevenin's circuit presentation ).? All this discussion is for a bandwidth from LF up to resonant frequency unless you want to design a broadband dummy antenna beyond the resonance frequency.
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Good Day,
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Raphael
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Yeh well, excuse my digression.
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I used to manage a department full of different project teams, so this sort of thing interests me. How to motivate people, and at the same time, get stuff out of the door.
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One of my favourite questions to ask interview candidates, and get a discussion going was - Engineering, is it an Art or a Science ?
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I come from the North of England, and an old saying there is "'Owt's better than nowt."
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Number 30 on the list.
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Back to the mundane stuff...
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Regards,
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Martin
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On Sun, Sep 29, 2024 at 01:42 PM, Raphael Wasserman wrote:
Are we here to discuss philosophical trends or solve some technical-engineering issues ? |
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Hi Martin
To answer your question.. its an art. I, me Simon know no where near as much theory as most on here do… yet I can look at an antenna ( say a Marconi T for 160m) and know within a turn or two on loading coil how many required, plus what L/ C to add to matching network..I can just “ see it.” Or an amplifier and make it work..however my Mum ( no longer here.) and Sister and I are artists..( paint, ceramic, (metal in my case..)) Cant explain it..just can. So i say its an art.. Simon g0zen Ps main job is on maritime vessels as engineer..( art dont pay.) |
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Martin,
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You raised a good question how to motivate people in engineering profession who hits the door of your department.
My question to them always was the same - what you can bring new to us ??
Every person who selected engineering profession and rising through his ranks knows very well where is the border between art and science.
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Have a pleasant day,
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Raphael
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