Talk:Halo antenna

Copied from my talk page: Thanks for making the halo antenna article more succinct!

Hello Interferometrist:

Thank you for your good emendations to the halo antenna article. I especially appreciate your skill at shortening the article without loosing substance, whereas I tend to put in too much. However there are a couple of things that I have issues with: One is already changed; the other will be in a few days.

I have reverted some of your more conservative reduction of the range of frequencies a small transmitting loop is capable of: Neither the upper nor the lower bound is "crisp"; both are based on what's tolerable, and what's feasible. The upper frequency limit at circumference = 1/3 λ comes from the difficulty tuning out the high reactances just above the frequency that gives circ. = 0.3 λ. The widely repeated 1/4 λ limit is a practical goal that most freshman antenna-builders can manage.

The lower frequency bound for small transmitting antennas is a matter of personal taste, and a consequence of skillful loop construction (or not). If you're a klutz, like me, you'll have to use a higher frequency limit around 1/8λ, since conductor resistance losses from poor construction will overwhelm the skimpy radiation resistance. If you can build or buy a very low-loss loop, and can tolerate the low R_R (and exceptionally dangerous voltages) you might be satisfied with performance at 1/10 λ, or push down to 1/20 λ, just to show off and / or see what it can do. At that extreme, of course, it might be the feedline that's successfully radiating, rather than the loop.

The point of this is that the bounds are subjective, based on what's practical for antenna building. As with all things in amateur radio, especially since some antenna designs and their names are now more than 100 years old, including small loops (think of Hertz's first experiments), the names people use now to describe antennas and radio parts are a mishmash of old and new, and strict and loose. Your pointed comments in your edit descriptions, though often valid, suggest that you think that the terms are or should be sharply defined. Some are (e.g. "balun" and "whip antenna"). Many are decidedly not precise (like "shortwave", "Windom antenna", "Marconi antenna", or "flat top"). (Another example: there is no frequency on the 40-meter band where the wavelength is actually 40 meters; likewise the 60, 20, 17, 15, & 10 m bands.) (And let us note that the so-called "UHF" (PL‑259 & SO‑239) connectors are not usable (with 50 Ω cable) on UHF or even upper VHF.)

As far as the definition of "small" loop, some (excessively) fussy writers declare that only 1/10 λ is sufficiently small, since they demand that for a loop to be a "small" loop, the current must be more nearly uniform than the current through a 1/4 λ loop, which is too uneven for formulas based on uniform current to be accurate. But please note: That is a subjective standard: The standard is based on how much error the objector finds tolerable in the impedance and radiation formula results. Even the dissatisfaction with a non-uniform current is based on the larger antenna not matching well the analytic assumption of uniform current. In essence it's as absurd as saying "Your feet are too big for your shoes." A better, less simple approximation is required (truncated sinusoidal, actually) for a 1/4 λ loop, rather than defining it off of the playing field for performance not conforming to the approximation. I say, make bigger shoes, don't demand smaller feet!

So please, temper your enthusiasm for precise amateur radio terminology; under this topic, precision is in short supply – not nearly available enough to suffice for your enthusiasm – and a lot of precise statements are based on personal, and arbitrary choices. I want your edits to keep on coming. I think almost all of the changes you made are legit and improved the article, but I fear you'll be frustrated to the point of switching to physics or mathematics, where the terms are (mostly) strict and clear. Some of your criticisms I found quite valuable: Like your demands for citations. I am indeed the one who wrote the footnote about half-wave and quarter-wave loops being merely a matter of frequency, because I've done it. You were very right to call me up short for using my own authority, rather than bothering to find a citation. That's why it's going to take a week or two over Christmas, digging through my reference books & articles, before I put the footnote back.

And please note that the point I was trying to hammer home with the remark in the footnote is exactly what I'm worried annoys you: The terms in use (like "halo" and "small loop") are just not that precise, and often are clearly flawed under minute technical examination. The "halo" fails the acid test by blissfully transmitting at half its design frequency, with just a bit more capacitance across the breakpoint, or an inductor near the feedpoint. (A wide reactance-range antenna tuner and high-impedance feedline help a lot.) As far as I can tell, in many cases, there are no authorities who present or enforce strict definitions. (For English terms the nominees might be the U.K. IEE and the U.S. IEEE, but my take on their online dictionaries of terms is that they're being carefully non-committal, and just trying to explain the gist of common use. I tried to include a link to the IEE glossary, but have lost track of it.)

Regards from soggy Oregon/
Dr. Tom Lougheed (K7TLI)

Astro-Tom-ical (talk) 05:34, 23 December 2020 (UTC)

@Astro-Tom-ical:Hi, thanks for the feedback. I'll quickly answer now and look at these questions again soon. Much of what you have written doesn't have to do with this page at all but with loop antennas, and only because of section 1 which compares the halo antenna to loop antennas which isn't the most important thing, in fact I only edited that section because it was already there and could be improved, whereas to understand the halo antenna one would learn about 1/2 wave dipoles which they are more similar to electrically.

I was not writing from a practical standpoint and perhaps you have much more practical experience with these (or with small loops) that could be put to use. I am starting from the standpoint of antenna theory and canonical designs, which for the small loop (or hertzian dipole) is VERY small (and impractical!) in order to justify the approximations involved and I haven't concerned myself with how large a small loop can get and still be "small" (nor is this dealt with in antenna theory books because I don't think there is a theory for it). Do go ahead and add practical info of this sort (that is, without theory but based on experience and rule of thumb etc.) but it should be subservient to the basic (albeit impractical) theoretical models.

I was a bit surprised that you all of a sudden started talking about transmitting small loops, because I believe that 99.99% of these are used for receiving (at least if they're still making AM radios), and a previous sentence specifically addresses "reception" with respect to pointing (as your edit reinforced!). Don't you think that sort of detail belongs on the Loop antenna page instead?

I'm afraid I have to leave now and will add to this further later, Interferometrist (talk) 04:55, 28 December 2020 (UTC)

Also copied from my talk page: Some suggestions on the halo article

I appreciate many of the changes you have made. I also agree with much of what Dr. Tom has said. However, I have a few comments.

I think we have more than enough information about small transmitting loops in this halo article. There is a reasonably good article on the small transmitting loop, and we do not need to overdo the comparison in this article, except to mention that the halo is close to a half wave in circumference, while the small transmitting loop is considerably smaller and thus need a large tuning capacitor. Actually a small transmitting loop becomes a halo as its tuning capacitor becomes very small. Thus I do not see them as radically different since one becomes the other in the limiting case. Of course as this limit is approached the pattern changes radically. So it really is true that definitions became a bit squishy.

As to the high voltage on the small transmitting loop, one of the serious design factors in a small loop is the voltage rating of the tuning capacitor. Voltages across it can be many thousands of volts. Most of the recent designs for small transmitting loops are fed with a small loop placed just across from the tuning capacitor. If properly sized, the feed loop has 50 ohms input impedance and no excessively high voltages anywhere near it. It is possible to feed a small transmitting loop by putting a relatively large capacitor in series with the smaller high voltage capacitor. In that case indeed there would be high voltage near the input terminals, but I haven't seen such a feed method used in practical antenna designs.(possibly because of the danger). Actually, since the current in the loop is taken to be nearly uniform, at least at the lower frequencies, a "matching" capacitor could be inserted anywhere, even on the opposite side from the tuning cap. But again, I haven't seen this done, since the loop feed method works so well. Or perhaps, I have misunderstood what you are saying about the matching method and high voltage points.

On very small receiving loops, a good rule of thumb is to make the diameter 1 meter or so regardless of frequency to guarentee that one hears "antenna noise". That is to say, the loop will pick up enough signal (or noise) to swamp the noise figure of the receiver input. However, many AM radios were built in the old days with considerably smaller loops. This was acceptable in most locations because man made noise was considerably more than the noise floor in a very quiet location, which was used to come up with the rule of thumb of 1 meter. If we take that rule at 540 KHz a 3.14 meter circumference divided by 555 meters wavelength is .0056 of a wavelength. Using the dimensions of the loops found in many radios of the era the number would be about .002 wavelength. Thus I don't think that the limiting value of 1/100 of a wavelength for small receiving loops is correct as mentioned in the article on loop antennas. The figure of 1/16 of a wavelength is very far off. Is it possible that you have in mind single turn receiving loops? Of course the small receiving loops consist of multiple turns. And in the old AM receivers,(and long wave direction finders) the multi-turn loop had a parallel capacitor and fed directly into the grid of the first tube as a high voltage, high Z source. JNRSTANLEY (talk) 13:00, 29 December 2020 (UTC)

I moved the discussion here and will get back to it, perhaps tomorrow, but I'm not feeling well and not up for it now. Till then, Interferometrist (talk) 07:43, 30 December 2020 (UTC)

I corrected a typo in my comments. JNRSTANLEY (talk) 12:36, 31 December 2020 (UTC)

Hello Interferometrist: Haven't heard from you, hope you are feeling OK again. I simply deleted the "advantage" related to high voltage, based on my comments above. Hope you find this OK.

JNRSTANLEY (talk) 12:29, 19 January 2021 (UTC)