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Thanks Bob, Steve and John for your suggestions.

A couple of days ago I received a message "Your Groups.i.o Account is Bouncing" and email delivery to my account has been suspended.? The problem is that I have no way of knowing who responded to my request. So if anyone other than the three gentlemen mentioned has responded, I would be grateful if they could repeat their reply.

Thanks again to those who did respond and cheers,

Chris VK4CVL

It seems that the inline images in my last message did not come through, so I uploaded them to the files section as described below.

Far field cardioid response:
/g/loopantennas/files/Unidirectional%20Coplanar%20Twin%20Loop%20%28CTL%29%20by%20Dr.%20Mike%20Villard/CTL-outer-loop-only-far-field-horizontal.png
/g/loopantennas/files/Unidirectional%20Coplanar%20Twin%20Loop%20%28CTL%29%20by%20Dr.%20Mike%20Villard/CTL-outer-loop-only-far-field-vertical.png

Magnetic near-field when illuminated from a far-field antenna located on the non-null side of the loop at x=100:
/g/loopantennas/files/Unidirectional%20Coplanar%20Twin%20Loop%20%28CTL%29%20by%20Dr.%20Mike%20Villard/CTL-outer-loop-only-magnetic-shadow-front-illumination.png

Magnetic near-field when illuminated from a far-field antenna located on the null side of the loop at x=-100, showing the "magnetic shadow" effect:
/g/loopantennas/files/Unidirectional%20Coplanar%20Twin%20Loop%20%28CTL%29%20by%20Dr.%20Mike%20Villard/CTL-outer-loop-only-magnetic-shadow-rear-illumination.png

Best regards,
--
qrp.gaijin@...

On Sat, Oct 15, 2022 at 12:43 PM, SP2BPD wrote:

The outer, larger-diameter high-impedance loop is resonant and is resistively loaded. As was already pointed out before, this resistive loading creates a unidirectional response. So the outer, high-impedance loop by itself produces a unidirectional response. I have confirmed this in 4nec2.

How did you get it? Where did you put the source on the outer loop? Could you provide nec file for it?

Good questions. The precise nature of your inquiry suggests to me that perhaps you have tried yourself to investigate this phenomenon in NEC, and perhaps you have encountered the same challenges that I have. I shall attempt to answer your questions in sequence.

How did you get it? (the unidirectional response shown by the outer loop of the CTL, without using the inner loop of the CTL)

I obtained the unidirectional far-field response of a single loop (the outer loop of the CTL) as follows. First, I modeled a CTL as described in Villard's article -- an outer, resonant, high-impedance loop with additional loading inductance and loading resistance; inside of which is mounted an inner, coplanar, resonant, low-impedance loop -- and adjusted it as described in Villard's aricle: tune the inner loop to resonance, then adjust the outer loop's resonating capacitance and loading resistance for best F/B ratio. For this procedure, the excitational current source is placed on the inner resonant loop, opposite of the resonating capacitance.

Then, to see the far-field cardioid response of the outer loop only, I removed the resonating capacitance from the inner loop, causing the inner loop to become a simple untuned excitational loop, as is often used with small transmitting loop antennas. I re-adjusted the outer loop's resonating capacitance and load resistance for best F/B ratio, plotted the far-field data, and observed the cardioid response.

Furthermore, to see the magnetic near-field shadow, I deleted the inner loop completely, and added a small vertical dipole (10 cm long) located 100 meters from the loop, either at x=100 for front illumination (from the non-null side of the loop) or x=-100 for rear illumination (from the null side of the loop). Front illumination causes a noticeable magnetic near field intensity to be generated in the interior of the loop. In contrast, rear illumination (from the unidirectional null side of the loop) can only cause a lower magnetic near field intensity in the interior loop -- this visibly lower magnetic near field intensity is the manifestation of the "magnetic shadow" that Villard repeatedly mentioned in his CTL articles that I referenced in my earlier post.

Where did you put the source on the outer loop?

As described before, I placed the excitational current source on a separate, untuned excitational loop, not directly on the CTL outer loop. I have not been able to generate the far-field cardioid response when exciting the CTL outer loop directly. It seems necessary to use a separate excitational element -- like a separate drive loop inside the outer loop -- in order to see the far-field cardioid pattern. The separate excitational element need not be a loop; it can also be a small dipole.

Could you provide nec file for it?

With pleasure. I am attaching (as inline text in this message, pasted below) two NEC files, created with 4nec2. The first file shows the far-field cardioid response of the outer loop, when driven by an untuned inner loop. The second file shows the magnetic shadow in the magnetic near-field, by using a far-field small dipole antenna to illuminate the CTL's outer loop, with illumination coming either from the front (non-null) side or from the rear (null) side. Each NEC file contains instructions on how to run the simulation.

For reference, here are the results I obtained from simulating these files in 4nec2.

Far field cardioid response:




Magnetic near-field when illuminated from a far-field antenna located on the non-null side of the loop at x=100:



Magnetic near-field when illuminated from a far-field antenna located on the null side of the loop at x=-100, showing the "magnetic shadow" effect:


I would be interested in hearing about any further research you might conduct in this area. Villard mentioned in his CTL articles that the load resistor on the outer loop is actually unnecessary, and that placing the smaller second loop a small distance away from the outer loop also allows the magnetic shadow to be generated. In other words, the magnetic shadow in the magnetic near field seems to be not necessarily confined to lie within the plane of the outer loop, but instead seems to extend (under some conditions?) outward from the plane as well. The exact shape of the 3D shadow region is still unclear to me, and it may be influenced by the exact position of the second loop.

Best regards,
--
qrp.gaijin@...


----------
File attachments follow.

----------

File 1: simplified-CTL-oneloop-with-untuned-excitation-loop.NEC

CM Partial model of Coplanar Twin Loop antenna at 7 MHz showing unidirectional far-field response from a single outer loop, corresponding to the outer loop of the CTL.
CM
CM The inner loop in this model is a simple untuned (non-resonant) excitational loop. The inner loop is not the resonant inner loop of the CTL. The use of an untuned, non-resonant excitational loop proves that the unidirectional null is caused primarily by the outer loop of the CTL, and does not depend on the CTL's resonant inner loop.
CM
CM Created in 4nec2 by qrp-gaijin@... (https://qrp-gaijin.blogspot.com).
CM 2022/10
CM
CE
GW??? 1??? 5??? -0.357143??? 0??? 1.1428571??? 0.3571429??? 0??? 1.1428571??? 5.e-4
GW??? 2??? 5??? 0.3571429??? 0??? 1.1428571??? 0.3571429??? 0??? 1.8571429??? 5.e-4
GW??? 3??? 5??? 0.3571429??? 0??? 1.8571429??? -0.357143??? 0??? 1.8571429??? 5.e-4
GW??? 4??? 5??? -0.357143??? 0??? 1.8571429??? -0.357143??? 0??? 1.1428571??? 5.e-4
GW??? 10??? 13??? -0.928571??? 0??? 0.5714286??? 0.9285714??? 0??? 0.5714286??? 5.e-4
GW??? 11??? 13??? 0.9285714??? 0??? 0.5714286??? 0.9285714??? 0??? 2.4285714??? 5.e-4
GW??? 12??? 13??? 0.9285714??? 0??? 2.4285714??? -0.928571??? 0??? 2.4285714??? 5.e-4
GW??? 13??? 13??? -0.928571??? 0??? 2.4285714??? -0.928571??? 0??? 0.5714286??? 5.e-4
GE??? -1
LD??? 0??? 11??? 7??? 7??? 0.1??? 0??? 7.337e-12
LD??? 0??? 13??? 7??? 7??? 1.10361e2??? 2E-05
LD??? 5??? 0??? 0??? 0??? 58000000
GN??? 2??? 0??? 0??? 0??? 13??? 0.005
EK
EX??? 6??? 4??? 3??? 0??? 1??? 0??? 0??? 0
FR??? 0??? 0??? 0??? 0??? 7??? 0
EN

----------

File 2: simplified-CTL-oneloop-near-field-illumination-from-far-field.NEC

CM Partial model of Coplanar Twin Loop antenna at 7 MHz, showing a unidirectional magnetic shadow.
CM Created in 4nec2 by qrp-gaijin@... (https://qrp-gaijin.blogspot.com).
CM 2022/10
CM
CM ---------------------
CM To view the near-field magnetic shadow:
CM
CM 1. For wire tag 100 (a distant signal source to excite the loop from the far field), set X1 and X2 coordinates to 100, placing the source antenna far along the positive X axis for illumination of the loop antenna from the front (non-null) side.
CM
CM 2. Run a magnetic near-field simulation over the domain x=[-2,2], y=[0.001,0.001], z=[0.5,2.5], with resolution of 0.01 meters in every dimension. In the results window, click anywhere in the plot to activate it, then from the menu set the maximum scale value on the plot to 0.010 A/m, and observe that the interior of the loop is brightly illuminated by the signal from the vertical dipole, as shown by a comparatively high magnetic near field intensity inside the loop. (The maximum scale value may need to be adjusted based on the actual field strengths.)
CM
CM 3. For wire tag 100 (a distant signal source to excite the loop from the far field), set X1 and X2 coordinates to -100, placing the source antenna far along the negative X axis for illumination of the loop antenna from the rear (null) side.
CM
CM 4. Run a magnetic near-field simulation identical to step 2, and observe that the interior of the loop is darker, indicating a lack of illumination by the signal from the vertical dipole, as shown by a comparatively low magnetic near field intensity inside the loop. This lack of illumination is the effect caused by the "magnetic shadow" effect of the outer loop.
CM
CM This is a proof-of-concept model to prove that a single, resonant, resistively-loaded loop (the outer loop in the CTL) can produce a unidirectional effect and can produce a magnetic shadow when illuminated from the rear (null) side.
CM
CM However, the magnetic shadow effect (as observed in the magnetic near field) seems to be stronger when using a second, low-Z, resonant loop inside the first loop -- this is the CTL configuration as originally proposed by its designer (the late Dr. Mike Villard). Perhaps, the magnetically-induced currents in the resonant inner loop serve to strengthen the magnetic shadow (further reinforcing the magnetic field in the non-null direction, and further canceling the magnetic field in the null direction).
CM
CE
GW??? 10??? 13??? -0.928571??? 0??? 0.5714286??? 0.9285714??? 0??? 0.5714286??? 5.e-4
GW??? 11??? 13??? 0.9285714??? 0??? 0.5714286??? 0.9285714??? 0??? 2.4285714??? 5.e-4
GW??? 12??? 13??? 0.9285714??? 0??? 2.4285714??? -0.928571??? 0??? 2.4285714??? 5.e-4
GW??? 13??? 13??? -0.928571??? 0??? 2.4285714??? -0.928571??? 0??? 0.5714286??? 5.e-4
GW??? 100??? 1??? 100??? 0??? 1.45??? 100??? 0??? 1.55??? 5.e-4
GE??? -1
LD??? 0??? 11??? 7??? 7??? 0.1??? 0??? 7.437e-12
LD??? 0??? 13??? 7??? 7??? 7.27259e1??? 2E-05
LD??? 5??? 0??? 0??? 0??? 58000000
GN??? 2??? 0??? 0??? 0??? 13??? 0.005
EK
EX??? 6??? 100??? 1??? 0??? 1??? 0??? 0
FR??? 0??? 0??? 0??? 0??? 7??? 0
EN

The outer, larger-diameter high-impedance loop is resonant and is resistively loaded. As was already pointed out before, this resistive loading creates a unidirectional response. So the outer, high-impedance loop by itself produces a unidirectional response. I have confirmed this in 4nec2.

How did you get it? Where did you put the source on the outer loop? Could you provide nec file for it?

Did you publish this on your Earthlink webpage??
If so, I know someone who probably saved it because he was impressed with all of your designs.
Do you recall the name?

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Hi Chris
G4AON published a 4 port active distribution amplifier recently.
There is a link on his QSL web page



Regards
Stephen, G4VBD

Hi all,

Decades ago I built a 4 port antenna splitter for the 10 - 30MHz range.? It is working quite well, but I find myself in a position where I need an additional one.? In the meantime I have lost the circuit diagram and coil winding details and tracing the circuit is going to be a nightmare. I wonder if anyone can point me to a 4 port HF antenna splitter (in a perfect world an active one to make up for the 6dB/port loss), but of course a passive version is also fine?

Cheers,

Chris

The CTL was one of several easy to make devices promoted by Villard as an external paid " Consultant" to the Voice of America to increase their audience numbers. So that's why these constructional projects feature consumer domestic radio's.

The CTL antenna has died a death as did the CFA, it has no magic new secrets, it's nulls are ill defined but? mostly much worse than a conventional loop if the given plots are anything to go by.

The CTL is a small inductively loaded loop resonated with a capacitor and loaded with a resistor. The outer loop is the major element.? Output comes from the inner loop which can also be resonated. Resonating the inner loop increases the signal amplitude by the working Q? value to couple into the high impedance broadcast radio.

Very surprising that QST published an article about broadcast reception in a Ham Radio journal where almost every reader would be very well able to receive extremely strong broadcast signals. The article contains so many misleading remarks, it is the exact opposite of good technical writing, it uses verbose pseudo terms and takes 6 + sides when two would be sufficient.


The Beverage Second Antenna ( r loaded Cardioid Loop) is ground independent but the modern versions use a ground with a vertical loop. This gives a higher e-field contribution. An extension of this idea is to use reactive as well as resistive termination to allow steerable sky wave nulling.

Interesting to note that the original Beverage in it's normal form is a resistively loaded vertical loop with the ground as a return path. It is desirable NOT to use the ground return for several reasons but that's another topic.

I am saddened that some people think the CTL is a wonder antenna capable of? further development, it is nothing of the kind. They have been misdirected by a bad article.

Regards,

Alan G8LCO.

On Thu, Oct 13, 2022 at 12:59 AM, Martin wrote:

The Low Z loop works as a standard H field 'magnetic' loop, and the second larger diameter Hi Z loop is more like an E field 'whip' antenna. When the outputs are combined (physical spacing) the resultant pattern is likely to be cardioid.

After thinking about the results of some old 4nec2 simulations, I think I have finally figured it out.

The outer, larger-diameter high-impedance loop is resonant and is resistively loaded. As was already pointed out before, this resistive loading creates a unidirectional response. So the outer, high-impedance loop by itself produces a unidirectional response. I have confirmed this in 4nec2.

What, then, is the purpose of the inner loop?

As was mentioned in post #16631 (/g/loopantennas/message/16631), on Sun, Aug 21, 2022 at 03:16 PM, Alan wrote:

When the resistor is added the original two nulls are filled in, at 90 degrees to the notches a new minima appears as the magnetic and electric fields partially cancel, increasing the resistor leads to a deep null when the two components cancel.? At this R value the cardioid ( heart shaped) pattern is formed [...]
The resistively loaded loop IS e-field sensitive!! so the advantage of e-field noise suppression is lost.?

We could take the unidirectional antenna signal off of the outer loop directly with a preamp or a toroidal transformer. But no, the CTL does something creative. The creator, Dr. Villard, seems to have realized that the interior region of the resistively-loaded outer loop exhibits a "magnetic shadow" effect -- the magnetic field for incoming signals from the null direction excites almost no magnetic field in the interior region of the loop (the "shadow area"), whereas incoming signals from the non-null direction excites a significant magnetic field in the same shadow area. So, there is a unidirectional "magnetic shadow" in the interior region of the loop, which I also confirmed in 4nec2 by plotting the magnetic near field data and exciting the loop with a distantly-located vertical dipole either on the null-side or on the non-null-side of the loop.

So: inside the magnetic shadow region, only magnetic signals from the null direction are suppressed, while magnetic signals from other directions are allowed to pass. All that remains to be done is to sense this local and shadowed magnetic field from the interior region of the large loop -- and this is the function of the interior, low-impedance loop, which is then connected directly to the receiver.

The same sensing of the local and shadowed magnetic field could probably be done with a simple and non-resonant inductive pick-up loop, but this would likely lead to a large loss of signal due to the lack of resonance. Making the interior loop resonant likely boosts the signal -- Dr. Villard (the CTL's creator) said that the sensitivity of the very small (table-top-sized) CTL was comparable to the sensitivity of the internal whip antenna of a portable receiver, indicating no drastic loss of sensitivity, even though no active antenna amplification is used.

Because the interior sensing loop responds primarily to the local magnetic field (thanks to its low impedance), it retains the advantage of suppression of local E-field noise -- which would not be the case if we attempted to extract the signal directly from the outer, resistively-loaded loop.

So Dr. Villard's main contribution seems to have been the recognition of the spatial existence of a magnetic shadow region in the interior of a unidirectional, resistively-loaded loop (which happens to be resonant, in the case of the CTL), and the use of a second, resonant, low-impedance loop (sensitive primarily to the magnetic field) to sense the shadowed (unidirectional) magnetic field.

I've been considering if it is possible to add regeneration to the CTL, and I think that adding regeneration to the interior loop only will boost performance while preserving the unidirectional property.

----

As an interesting aside, Dr. Villard also designed an antenna to exploit an electric-field "shadow region", although such an antenna, being E-field sensitive, is more prone to detuning by nearby objects and persons. This antenna uses two whip antennas (similar to the two loop antennas in the CTL) and is described at the top of this page: . Another detailed description, with a picture of the antenna, is here: . This two-whip-antenna is also briefly described here: -- see the section titled "Antennas Generating Nulls in the Ambient Electric Field".

At a quick first glance I think it is operating pretty much as a standard cardioid loop.

The Low Z loop works as a standard H field 'magnetic' loop, and the second larger diameter Hi Z loop is more like an E field 'whip' antenna. When the outputs are combined (physical spacing) the resultant pattern is likely to be cardioid.

As an example of something similar, I have an old NDB band DF antenna that uses a tuned ferrite rod, and it has a small metal tab which you touch to unbalance the antenna, and which will (hopefully) allow you to resolve the 0/180 degree ambiguity.

Just a theory, but I'm fairly sure it's something like that.

Regards,

Martin

I'm late to this discussion, but would like to add a comment about another unidirectional small loop antenna design.

Steve, I apologize for giving an incorrect description of this group to the OP. I stand corrected! Thank you.

73, Joe K9LY

On Tue, Oct 4, 2022 at 08:51 AM, John wrote:

The 1788 covers 10-30 Mhz and the 1788 covers 7 Mhz to 21Mhz

Should be?1786?covers 10-30 Mhz and the 1788 covers 7 Mhz to 21Mhz

John VE3IPS

Double check all solder joints as the QC can be? poor at MFJ

Can you believe the minimum wage in Mississippi is $7.25 an hour and congress wonders why there is such poverty??

I don't want to be forced to pay a guy to fix my loop antenna more than he is worth.

The 1788 covers 10-30 Mhz and the 1788 covers 7 Mhz to 21Mhz

John VE3IPS

Double check all solder joints as the QC can be? poor at MFJ

Can you believe the minimum wage in Mississippi is $7.25 an hour and congress wonders why there is such poverty??

Hi

Yes mag loop group is all about trx loops, HOWEVER the knowledge on here is supreme.. I see no issues with posts about mfj or whatever here..

Think about it..no one with real estate in middle of nowhere would use a loop of any kind..why would you?

So if using small active rx loops or tunable rx loops then one may well have experience on trx loops..I do..I have to due to my location..

Also original poster was quite clear in request..yes?

Just my 1penny worth..Simon g0zen

开云体育

Agree, but I was responding to the list owner's posting on this thread.? Gets complicated.

Dexter

Being the OP of this thread, I was subsequently reminded that for "transmitting loops" I should have posted my question on the "Mag Loop" Group forum instead of to this Group.? However, my reference to MFJ-1786 and MFJ-1788 (the Subject line of Dexter's post) are well known models that I did not believe required further elaboration. Perhaps Dexter's post needed a new Subject heading such as "Suggestion to describe type of antenna" or some such rather than a continuation of the MFJ thread.