Just saw this - looks like it might be worth trying...



Roger

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One wonders if a copy/ based upon Ccw cardioid loop.. which itself is based upon a military 70’s loop if it is i run 2 on 160m ( but bigger.)

Cross country wireless

Google..

Simon g0zen

A loop with a resistor to produce a unidirectional pattern was patented by Harrold Beverage in 1941, since then the idea has been periodically "re-invented" by many individuals but the idea is very well known to people interested in Antennas. You can find the original patent at US 2,247,743, Beverage applied for the Patent in December 1938 so the examination took some time!

So when People claim to have discovered or invented the idea they are too late or? ignorant of the history. No one mentions the true originator although his very long wire on or just above ground is normally regarded as THE Beverage antenna.

Basically the added resistor is opposite the feed point ( it can be elsewhere though), the loop then becomes sensitive to the electric field as well as the magnetic. 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, at 90 degrees the former notches are replaced by a unity gain, 180 degrees from the null is a double level broad peak. It is a very simple pattern to calculate for an angle a ( for a small loop), the base figure of 8 is? A= Cos a,? the combination is? A=1 + Cos a as the vertical e-field component is omnidirectional ( 1 for any angle).


This is not a miracle antenna, it's simple physics in action. The resistively loaded loop IS e-field sensitive!! so the advantage of e-field noise suppression is lost.? One interesting application is as part of a very directional array. C & S Antennas used a cardioid R loaded broadband loop with an active amplifier as elements in an array to produce broadband directivity for Mil and Com applications. It's also been very widely used as a handheld DF antenna by R & S. Triangular and rectangular loops with resistors are also well known. Nothing new at all!

Regards,

Alan G8LCO

On Sun, Aug 21, 2022 at 03:16 PM, Alan wrote:

Triangular and
rectangular loops with resistors are also well known. Nothing new at all!

Regards,

Alan G8LCO

Thanks Alan for your interesting historical perspective.

Roger

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Andrew and Geoffrey both mention Keen's books. For anyone interested in Loop Antennas Ronald Keen's books are very interesting, there are three titles but updated versions can have more data! :-

• Direction and position finding by wireless 1922
• Wireless direction finding and directional reception 1927
• Wireless direction finding 1938 (revised 1947)

They all contain a lot of material which may be new to many people, some ideas long forgotten and a great deal of material? which is now called by different names.
In the 1938 edition you can find the Low Noise Vertical (before it was re- invented recently) , Twin crossed in-line loops and spaced loops ( now largely forgotten). You can also see the origins of E-Field active antennas which were used as the sense antenna ( using a valve amplifier).
The 1938 version can be found on-line. One problem is that the Ronald is miss-spelt by? ?to become? Donald, Roland and now Richard!
The last edition of 1947 included WW2 developments including Huff-Duff which was a CRT displayed automatic HF DF which played a very important role in defeating U-Boats. One of my fave tech books.

Regards, Alan G8LCO

The 1922 edition of Keen's 'Direction and Position Finding by Wireless' is here:

I found the 1922 book on archive.org and the PDF is a good file.
<https://archive.org/details/DirectionAndPositionFindingByWireless>
<https://archive.org/details/directionandpos00keengoog>
<https://www.google.com/books/edition/_/u6RRAAAAMAAJ?hl=en&gbpv=1>
It looks like the source book came from the University of Wisconsin - Madison
and was scanned by the Google books project.

The 1938 version of Keen's book available at this link...



Roger

Nice link, Roger.
Strip off the book name and the root directory has a lot of stuff to look at.
<https://archive.org/download/radio-direction-finding-documents/>

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

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

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.

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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".

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.

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?