“Leigh’s Wrap-up Conclusions”.

 

From: Leigh Turner [mailto:[email protected]]
Sent: Sunday, 28 September 2008 12:12 PM
To: 'Lloyd Butler'
Cc: 'John Elliote'; 'Rob & Carlein Gurr'
Subject: RE: 1.8MHz Loop some concluding words / few more words
Importance: High

 Hello Lloyd, 

This is such a fascinating subject, so a few more quick comments in relation to your latest references 1 and 2 below. 

I think G3LHZ’s main point is that critics of his findings of high intrinsic loop efficiency have been mistakenly ascribing these very significant external losses to the loop itself.  The ground losses immediately beneath the loop are universally accepted to be potentially high and can drastically alter performance; and any antenna, not just loops, deployed in such lossy environments will perform poorly / less than its capability compared to being sufficiently distanced from these deleterious losses.  However, the loop antenna (with its predominant and localized magnetic near field) is nearly always shown to be the best choice and by far the most environmentally tolerant when the antenna has to be of restricted size and mounted relatively close to the ground; this is particularly so for the low bands of 40/80/160m where small loops excel over almost any other alternative antenna type on a wide variety of propagation paths.  The ground loss under a loop antenna as a function of height can be readily assessed.  Excessive ground loss can of course be mitigated by placing a modest sized conductive ground plane underneath the loop. 

Vertically oriented small loop antennas perform very well at low heights because in the near field (confined to just a few loop diameters) most of the loop's field component is magnetic H-field and magnetic losses in ordinary ground are considerably less than the dielectric losses that most antennas (i.e. dipoles) with a large electric E-field component are subject to.  In a small loop antenna with a top-mounted tuning capacitor the displacement currents are instead highly concentrated in the small region of space between the capacitor plates, and the adjacent ground proximity plays little or no part in supporting those return RF currents.  However, at a larger distance from the antenna where the far-field has fully formed the far field energy will still be unavoidably affected by the lossy ground.  This is of course why HF loops work so exceptionally well onboard ships and sea vessels. 

We can also say that any RF power lost into the local environment (lossy ground or eddy currents in nearby ferrous objects) in proximity to the antenna must, by definition, have first been transmuted into EM fields; the reactive near-field / induction energy storage field, the radiating near field, and far-field radiation, and therefore such losses should not be mistakenly included in the Rr part of the antenna efficiency calculation, i.e. in calculating the 1.8 MHz small loop antenna efficiency they must be properly ascribed to loss resistance, not an artificial augmentation of the antenna’s radiation resistance*.  Now separating and quantifying these reflected / transferred loss components in the antenna’s equivalent circuit from the loop’s true radiation resistance is not always so easy! The amount of energy dissipated as heat by the external lossy medium directly and profoundly effects antenna efficiency. The ground induced losses can easily dwarf the loop’s very small radiation resistance at the lower frequencies.  Of course the induced ground currents also contribute to the antenna’s total radiation field.  Alas, nothing is simple.

 It is interesting to note that G3LHZ has observed large (approx 3:1) variations in the measured Q of a loop sitting on a wooden table as the ground moisture level / conductivity changes over the course of a hot sunny day after a previously wet night; indicative of how such transferred losses have a profound influence.  Such an empirical observation of environmental sensitivity is also highly suggestive the loop structure itself is indeed efficient.

 Now in relation to your reference 2 below, we can note that feeder radiation has a markedly different radiation pattern and polarization characteristic from that of the loop mode radiation and is easily differentiated, so attributing too high a loop efficiency solely to feeder radiation can be readily ascertained and oftentimes dispelled by simple measurements.  The definitive acid test of demonstrating precisely where the predominant radiation contribution is coming from is to elevate the small loop on a tall rotatable mast high above ground.  If the radiation were to be primarily emanating from unbalance currents on the vertical feeder coax, then rotating the loop would be a completely fruitless exercise.  Since it isn’t, and we typically experience useful sharp pattern nulls, we have a conundrum.

 I’ll make an additional concluding comment to encapsulate much of what I’ve already said in this chronology over the efficacy of an electrically small 1m diam loop for the 160m band (what I believe in this case is excessively small).  I accept that such a small loop is indeed intrinsically efficient as G3LHZ asserts; it’s an efficient modal transducer of electrical energy into EM fields, and will produce a useful far-field radiation component; particularly if it is sufficiently distanced from the external ground losses.  However, its practical utility is severely limited by the high Q and resultant narrow bandwidth. The Q of each antenna mode being formed by the ratio of its stored to its radiated energy.  While all modes contribute to the localized reactive power, the radiated power of a loop antenna is calculated from the propagating modes. As the loop becomes very small in relation to a wavelength, eventually no propagating modes exist hence the Q of the system becomes very large because all modes are evanescent / below cutoff and contribute very little power.  However, unlike closed waveguides, each evanescent mode does have a real part, albeit very small. In the extreme case an infinitesimally small loop (Diam << λ) will behave as a lumped L-C tank circuit element with no radiation field.

 The limit of a very small loop’s practical utility is therefore determined by its instantaneous bandwidth (whether or not it supports the desired modulation signal components) and whether it produces a strong enough component of far-field radiation / sky or ground wave signal to yield a sufficient SNR over a given communication link / 1.8 MHz propagation path.

 Kind regards,
Leigh
VK5KLT

 

* Note; many antenna neophytes fall into this trap when improperly installing Vertical antennas or electrically-short mobile HF monopole whip antennas without a sufficient ground system or efficacious number of radials to adequately image the missing half of the radiating element; they are deluded by the extra transferred ground loss yielding a perfect VSWR match and the illusion of their being a large amount of power radiated in the antenna’s (usually small) radiation resistance!

 


From: Lloyd Butler [mailto:[email protected]]
Sent: Tuesday, 23 September 2008 10:42 PM
To: Leigh Turner
Cc: 'John Elliote'; 'Rob & Carlein Gurr'
Subject: Re: 1.8MHz Loop some concluding words
 

Hello Leigh 

Thanks for your comments on my Concluding Words
Just a few added comments relative some of your own further dialog:    
 

Reference: [VK5KLT comment]  Mike’s 70 % figure for the small 1m diameter loop is the intrinsic efficiency of the loop resonator itself;  

Well I can't say I really understand what you mean to imply by using the adjective "intrinsic" to qualify "efficiency". (My old Oxford dictionary equates ""intrinsic" to "inherent"). But I think we are talking about radiation efficiency of the loop itself assuming it is not influenced in any way by the surrounding objects. (But as I have said before, I think it actually has to be influenced operating at 1.8 MHz in the home backyard).    

If I read efficiency of an antenna, I assume radiation efficiency, that is, ratio of power directly radiated from the loop itself to power fed into it. If much of the power is being coupled into something else by induction, it is not being radiated by the loop itself, even if the secondary object (which accepts the power) is regenerating that energy as radiation. 

Take away the secondary object and the coupled energy will not occur and you are left with the real radiation which the loop is able to emit.   Real radiation efficiency of the loop is the ratio of that radiation to power fed into it. 

Even if one considers the radiation efficiency of the loop assembly as a system, taking into account regenerated radiation energy via coupling into a secondary object, the efficiency of the system is somewhat undefined. If the object were a surrounding low resistance loop, maybe most of the coupled energy would be regenerated as radiation. (In fact this precise phenomena is applied in the OH3FER coupled loop idea). But if the secondary object had high loss resistance (such as a lossy earth), then most of the coupled energy would be dissipated in the loss resistance.  

About all one can say is that the 70% is the proportion of power not dissipated in the loop resistance of the loop. It certainly cannot be taken as the proportion of power radiated directly from the loop nor the proportion of power assumed to be radiated from the loop system in the practical environment anticipated for the 160 metre installation.  

Again on the other question I previously raised, if part of the 70% is due to radiation from an unbalanced feedline, that part is certainly relevant to the radiation efficiency of the antenna as a system but not relevant to the radiation efficiency of the loop itself in isolation. 

Reference: " I’d expect that Mike would have deployed a current balun or ferrite choke of sufficient impedance at 1.8 MHz to choke off any imbalance currents flowing on the coax feedline outer conductor. " 

Well there is nothing in his document supplied with his talk to indicate that he did in fact use such a choke. But assuming that he did, from my own experience with in line coax chokes, I know that it would be very difficult to produce sufficient inductive reactance at 18 MHz to be high compared to the unbalanced longitudinal circuit impedance at the coupled end of the coax line.

 I now know from my own measurements that a surprisingly high degree of current unbalance is generated in the coax feeder when a resonant antenna (very small compared to a wavelength) is coupled unbalanced. This might certainly be the case in using the 1 metre loop at 1.8 MHz with the gamma match.

 Before I could accept that this did not happen in Mike's experiment, I would want to see evidence that the currents in the legs of his coax feedline were balanced. Having nicely established that they get 1:1 SWR on their feedline, it is not something that most experimenters  would then proceed to carry out.      

In support of that last sentence, I recall that in the large discussion group on the EH antenna, including both those who figured it must be radiating from the feeder and those who were not prepared to accept that, only one person in the group took the trouble to measure for the presence (and/or magnitude)of current unbalance in the coax line. That person was able to confirm my own measurement results.

If I was still living Panorama with ample space and plenty of trees to hang up a 1 metre loop with the gamma match, I guess I could  make some coax balance measurements with test loop to check all this out for myself.  But I guess I will just have to wait and see if someone else gets around to looking at this more carefully.    

OK about your forthcoming visit to UK and the chance to look up Mike and see for yourself his gear and experimental set up. That should be good. 

My wife and I have been twice to tour around Europe and UK. But I think our increasing age gradually puts a few restrictions on our ability to withstand long overseas trips and I don't think we will be traveling too far away from home in the years ahead.  But that's life - eventually elapsed time catches up with all of us.    

 Best Regards
Lloyd
 

----- Original Message -----

From: "Leigh Turner" <[email protected]>
To: "'Lloyd Butler'" <
[email protected]>
Cc: "'John Elliote'" <
[email protected]>;
"'Rob & Carlein Gurr'" <
[email protected]>

Sent: Thursday, September 11, 2008 10:25 PM
Subject: RE: 1.8MHz Loop some concluding words

 Dear Lloyd,
Many thanks for sharing your well considered and highly compelling conclusions; I have commented on them tonight in some considerable detail in the attached document (my various comments in blue text interwoven with yours).

First of all I must explain the recent hiatus in our lengthy and most enjoyable discussions; rather than running their course, the fascinating subject of small loop efficacy had merely taken a back seat position over the past month or so. I'd spent a good portion of July and August away on separate trips to the USA, as well as being immersed in a complex landmark US patent infringement litigation case that's consumed an inordinate amount of my time and focused attention with numerous reports, depositions and court testimony in Chicago.

Nevertheless I always find a welcome diversion such as this into fun amateur radio and antenna topics quite irresistible.  :-)
 
I think you'll find our views on the subject are pretty much aligned.
73
Leigh
VK5KLT

 ATTACHMENT 

COMMENTS & DISCUSSIONS ON THE SMALL TRANSMITTING LOOP ANTENNA

SOME FINAL CONCLUSIONS

Lloyd VK5BR

A lot of discussion has taken place between Leigh Turner (VK5KLT) and myself concerning the small transmitting loop antenna essentially following on from questions I had raised concerning the talk by Mike Underhill G3LHZ on small antennas. My questions, in particular, concerned test results from Mike which seemed to indicate that a 70% radiation efficiency could be achieved at 1.8 MHz using a 1 metre diameter loop.

[VK5KLT comment] Mike’s 70 % figure for the small 1m diameter loop is the intrinsic efficiency of the loop resonator itself; it is not intended to include and take into account any external loss factors such as that caused by the immediate environment. In many practical deployment scenarios these "extrinsic" factors will of course greatly influence losses and have a profound bearing on where RF power is distributed. The only way to escape these deleterious and dominant influences would be to elevate the loop under test to a great height above ground on a sky hook or some such contrivance to achieve a pseudo free space environment; or at least a distance well outside of the loop’s near-field boundary approximated by λ/2π. Alternatively, the loop could be mounted in a vertical orientation over a large expanse of conductive ground plane / ground mat at a more modest height of a just few loop diameters. Since the antenna is so electrically small a relatively small ground plane is adequate. HF loops are often deployed in professional applications on elevated building rooftops with short masts mounted on copper foil / mesh or aluminium ground sheets.

The essence of Mike’s measurements and observations is that the majority of the RF input power is not dissipated in either the loop conductor or the tuning capacitor, i.e. the antenna structure per se. This assertion seems to have created quite a controversy amongst the experts and antenna commentators.

Low and behold the energy is going into EM field creation; the sole purpose and function of any antenna.

LEIGH'S RECOMMENDATIONS

Leigh Turner has studied the theory of the Loop in depth and has had a lot experience with practical loops. Based on many factors including such as radiation efficiency, operating Q suitable for SSB operation, he has come up with recommendations for design. I copied two paragraphs from one of his articles: 

"Transmitting loop antennas intended for optimal coverage of the HF spectrum from 3.5 MHz to 30 MHz are best segregated into at least 2 distinct loop sizes. A nominal 0.9m diameter loop for covering all the upper HF bands from 20m through to 10m (and perhaps also tuneable down to 30m depending on capacitor min/max ratio), and a 2m diameter loop for covering the lower bands 80m through to 30m. For best operation down at 160m and improved 80m performance an increased loop diameter of 3.4m should be considered."

"The conductor diameter is determined by the desired loss resistance due to skin-effect, and choices can range from 6mm copper tubing to large bore 100mm copper or aluminium tube. Commonly used conductor diameters used to fashion the loop are 20mm and 32mm soft copper tube."

Of course Leigh's complete article is much more comprehensive than that but I thought the two paragraphs on their own give a good initial feel to the sort of sized loops one should build to get good results on the amateur bands. This is excellent material and I certainly accept his recommendations.

INDUCTION INTO GROUND OR NEARBY OBJECTS

But I am still concerned about this 70% at 1.8 MHz. First of all let me relate some practical tests on short fat dipoles and effects of direct induction the lower frequency HF bands:

I constructed short fat dipoles for 10, 20, 40 and 80 metres. For each of these, the dipole length was around 2% to 2.5% of the wavelength and each dipole was loaded balanced with inductors in each leg to bring the antenna to resonance at the relevant frequency. Based on formula used to calculate radiation resistance (Rr) for a basic short dipole, a value of Rr was anticipated of about 0.1 to 0.2 ohms for the simple dipole mode.

Loss resistance (RL) was assumed to be mainly that presented by the summed loss resistance of two coils in connected in series. The values measured were as follows:

10 metres RL = 4 ohms

20 metres RL = 8 ohms

40 metres RL = 9 ohms

80 metres RL = 14 ohms

Each antenna was hung up under a bow of my willow tree about 2 to 3 metres above the ground and the resonant series resistance directly into the dipole via the inductors was measured using an impedance analyser. The resistive components measured as follows:

10 metres - close to the 4 ohms loss resistance

20 metres - slightly greater than the 8 ohms loss resistance

40 metres - 14 ohms

80 metres - 25 to 44 ohms (very variable depending on the precise height the antenna was above the ground.).

The simple dipole mode radiation resistance is so small that it is negligible compared to the coils loss resistances. So what we see at 10 metres is simply the loss resistance presented by the loading coils.

But what is happening at 80 metres to provide such a large value of measured resistance? Surely not radiation because it does not occur on the similarly constructed 10 metre antenna! But for the 80 metre antenna, the distance between the antenna and the ground (and the tree) is a much smaller proportion of a wavelength than that for the 10 metre antenna. My conclusion was that in the case of the lower frequency (or longer wavelength) antennas, considerable power was being coupled by direct induction into the ground and the tree.

[VK5KLT] Wholeheartedly agree with this assertion. Such induction losses were certainly occurring.

I didn't make a 160 metre short dipole but my guess is that if made in the same form and measured in the same location, an even higher resistance would have been measured.

[VK5KLT] Yes, this even higher loss component with a 160m dipole would have certainly been the case.

Now let' get back to Mike's 160 metre loop of about 1 metre in diameter or about 3 metres in circumference. We might think of this as a dipole length of about 2% of a wavelength folded around and in this case, brought to resonance by capacitance across its folded ends. Clearly a different pattern for the two induction fields. But (like the short dipole) why should coupling not occur via these fields into the nearby earth or objects which, for 160 metres, are most likely to be spaced a mere fraction of a wave length from the test antenna.

[VK5KLT] Near field coupling of power into the adjacent ground and other nearby objects would indeed occur. See my above comment #1 for techniques to avert or mitigate these deleterious influences.

Mike was able to prove by measurement that 70% of the power fed to his loop was not lost in the resistance of the loop. He assumed this was power radiated but we are talking about a wavelength of 160 metres. Unless it were possible to make the measurements far enough away from ground or other objects relevant to this wavelength, radiation as the only reason for the 70% can hardly be assumed.

[VK5KLT] Agreed. However, there are only 3 places the input power can go:

1)  I2R self-heating of the loop conductor / tuning capacitor and the ultimate destruction of the loop

2)  into the loop’s radiation field

3)  into adjacent lossy ground or nearby objects

I think Mike was asserting the input power was going into field creation; a proportion of which is the radiation far-field useful for HF communication purposes. Now assuming the normal lossless energy exchange is allowed to occur in the loop’s surrounding near-field in a relatively unimpeded manner, a large proportion of this localized stored energy will be transmuted to the radiation far-field and formation of the loop’s lobe pattern.

Now of course any usefulness for radio communication purposes presupposes the loop’s radiation Q and associated instantaneous bandwidth are capable of supporting the desired Tx modulation mode. This aspect will inevitably be problematic if the loop dimensions are too small and the structure has a too high a Q. These factors are encapsulated in my practical design recommendations cited above. 

Had I not detected from measurement the increase in antenna resistance in the short dipoles at low HF frequencies, I would not have had reason to wonder whether the same thing occurred at low frequencies with the small loop. As the direct induction effect did not occur for the 10 metre short dipole, I have wondered what the results of Mike's tests would show if his loop (operating at 1.8 MHz) were scaled down for an efficiency test on 10 metres so that proximity to ground or surrounding objects was much larger when compared to the wavelength. (The loop would be scaled down by a factor 160/10 so that the loop diameter was 6.25cm in diameter and the copper tube diameter was 0.625mm). This would seem to be the way to either prove the existence of coupling due to direct induction at the lower frequencies (such as at 1.8 MHz) or eliminate it as a factor.

[VK5KLT] Lloyd, this was a good and highly pertinent empirical observation about the 10m short dipole. What I deduce from this experience is the lossy ground and the tree was outside of the λ/2π boundary zone distance from the antenna structure. I don’t see any need at all to prove the existence of direct induction coupling losses at the lower frequencies; that is taken as a given whenever lossy materials such as ground or moisture laden trees are introduced in adjacent proximity to the antenna’s near field!

It’s all about the localized extent and orientation of the antenna’s near field in respect of proximity to these lossy materials; 160m electric dipoles and magnetic loops differ greatly in this regard and is one of the reasons why well designed and appropriately sited small loop antennas give such good accounts of themselves. Their performance always belies their diminutive size compared to a full resonant length λ/2 dipole for 160m.

Unfortunately trying to scale a loop is fraught with difficulties and complications as the various loop radiation modes do not scale with frequency. The skin effect conductor losses increase as the square root of frequency and the radiation Q is inversely proportional to absolute size and not to frequency. 

RADIATION FROM THE COAX LINE

Another question I raised concerned the degree of balance which might be achieved in using the gamma match for coupling the coax line as used in Mike's loop. The question raised was whether some of the 70% of power assumed radiated from the loop might have actually been radiated from a longitudinal current component in the transmission line. This could develop a longitudinal current component running in the line.

[VK5KLT] This is a valid concern and potential issue, and we are reliant here on Mike’s presumed efficacious attempts to control and limit such incidental radiation from the feedline. I’d expect that Mike would have deployed a current balun or ferrite choke of sufficient impedance at 1.8 MHz to choke off any imbalance currents flowing on the coax feedline outer conductor. This was my understanding from past conversation with Mike on this aspect of his experimental setup.

Leigh supplied data on commercial loops where the makers went to pains to ensure the coupling was well balanced and chokes were placed in the transmission line to inhibit a longitudinal component. However, Mike's test antenna appeared to be gamma matched and this form of coupling doesn't appear to be immune to the development of some radiation from the line. The unbalanced bi-directional radiation pattern (as supplied by Leigh) for one commercially made antenna seemed to demonstrate this.

[VK5KLT] The gamma matched loop feed structure would be more vulnerable to developing an unbalanced longitudinal current flowing on the coaxial feedline outer shield conducive to producing spurious feeder radiation.

I will again refer back to my short dipoles. Connected in the balanced form via a transmission line, currents in the two legs of the line were measured as equal. However if connected unbalanced, current in one leg was read as about double the other. As explained in some of my articles, the effect of the high Q tuned antenna at the end of the line seemed to multiply the degree of current unbalance. I further suspect that if the high Q loop were not quite balanced, the same effect might occur in multiplying the degree of current unbalance in the coax line legs.

[VK5KLT] Yes indeed, this phenomenon may well be coming into play with some of Mike’s loop feed configurations.

A check for current balance in the legs of the coax line could easily be made inserting RF ammeters in each leg of the line feeding the antenna. If the currents were measured as unequal then at least some of the assumed radiation from the loop must surely originate from the line rather than the loop itself.

[VK5KLT] Lloyd, I guess much depends upon Mike’s relative proportions of loop and feedline radiation. Hopefully Mike had configured his measurement setup to minimize the latter. I’m sure Mike is experienced and savvy enough in his experimental procedure so as to not screw up on such a fundamental issue as this.

This is where the critics of Ted Hart W5QJR over his EH antenna embodiment and the controversial CFA may well have a valid point. I think that anybody proposing and advocating an unusually small antenna whose operation and performance appears to defy that predicted by traditional antenna theory must bear a considerable additional burden of proof to show and disprove that such "magic" radiation is not emanating from the feedline!

Many antenna designs work because of common-mode currents, rather than working in spite of them; and the acid test is whether or not they become significantly poorer radiators (wet string?) if common-mode currents <http://www.w8ji.com/common-mode_noise.htm> on their feedline are eliminated with an effective choke balun. Such as how the small EH antennas perform poorly compared against full sized benchmarks when these feed choke precautions are taken.

There are many small "miracle HF antennas" on the market whose performance is predominantly based on unbalance currents on the coaxial feed line. These "antennas" are in reality not antennas in the proper sense of the term; it is more correct to call them "top mounted coupler or tuning devices" which couple to the coax screen outer conductor via displacement current from antenna surfaces with a high RF potential. Here the misguided inventors and untruthful vendors not only make a virtue from necessity; they have essentially swallowed their technical pride.

Installations using such diminutive "miracle antennas" may work fairly satisfactorily for HF communication if a mainly vertical feed line of appropriate length and a good RF ground connection are used - at least this declaration must be said to be honest! Often these miracle antennas are marketed by fancy and loquacious "Mickey Mouse" theories about new laws of nature which have never been verified in the laboratory - attempts by hapless amateurs to successfully apply them will only make an experimenter annoyed and disappointed when eventually realising they been mislead or "taken for a ride," considering the cost of the so called "breakthrough" small antenna device.

 FINALE

(1) The 70% efficiency for Mike's loop at 1.8 MHz was derived from practical tests and measurement. His methods of separating power lost in the loop resistance from the total power are fine. What seems to be missing is any form of further testing to verify that the 70% of power (assumed as direct radiation from the loop) is not due (at least in part) to direct induction into the ground or nearby objects. As I have demonstrated with my short dipoles, one way this can be done is to scale down the operating wavelength and the proportional loop dimensions, to a point where direct induction effects can be considered minimal.

[VK5KLT] Agreed; I think the test procedures required to throw light on this important matter of where the power is going with these small 1.8 MHz loops are straightforward and have been outlined in my various comments above. As mentioned, scaling the loop has severe limitations impacting on the validity of the results.

We must also recognise that power being absorbed into lossy ground is not a problem that’s confined to magnetic loop antennas; it’s a universal problem influencing all antennas at the longer wavelengths where insufficient separation distance from the structure’s near-field zone cannot be easily achieved.

(2) There is also the suspicion that some of the 70% power might be radiated from the feedline in Mike's gamma matched loop. An RF ammeter in each feedline leg could easily check this. (I note that this must have been of some concern in feeding these loops - refer to the inclusion of the balun in the coax line of the Tampere OH3FER sample).

[VK5KLT] Yes, there’s probably some additional radiation from Mike’s preferred and often deployed gamma match feed mechanism; but probably not a great / dominant amount as the lobe patterns and null locations pretty much follow classic form. I think the OH3FER design included a ferrite balun for good measure to ensure purity of the pattern and keep any RF from getting back into the rig. It’s almost a routine habit at my QTH to include a toroidal core common-mode choke in any HF antenna coax feedline.

My wife Glenda and I are planning a vacation in the UK scheduled for early 2009 and visiting with Mike and Jill down in Surrey is on our travel itinerary. I will therefore have an opportunity to see Mike’s home laboratory and experimental antenna setup and plenty of time to leisurely discuss and debate many of these practical and philosophical questions about his findings on loop antenna characteristics.

Lloyd



-----Original Message-----
From: Lloyd Butler [mailto:[email protected]]
Sent: Monday, 8 September 2008 11:24 PM
To: Leigh Turner
Cc: 'John Elliote'; 'Rob & Carlein Gurr'
Subject: 1.8MHz Loop some concluding words

To Leigh, Rob, & John
 
The lengthy email discussions on loops seem to have run their course.

But my original doubts on the conclusions drawn from Mike's tests of his 1
metre loop at 1.8 MHz still remain.

The attached doc file discusses why.

Best Regards
Lloyd VK5BR