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Author Topic: Villard Cage: very accurate electrical noise locator  (Read 4288 times)
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km6sn
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« on: October 16, 2020, 11:08:08 PM »

This is to describe a direction finding device is called a Villard Cage("CAGE" herein).

The CAGE is sharp enough you can find an offending power pole, and identify
which crossarm is the noise source, and even which side of the crossarm
is the noise source.

It was developed by Oswald Villard, probably while he was doing early
research on over-the-horizon radar.

Google Oswald_Garrison_Villard_Jr

I have tried in vain, but documentation on the CAGE is apparently lost to history.

WHAT IT IS

It is an electrostatically shielded dipole, with a VHF AM  receiver.

Imagine a section of rain-downspout, about 36 inches long. Now cap each end
with a pyramid of sheet metal. With that view in mind, image the CAGE being
built with wire-frame construction instead of a downspout-and-sheet-metal-pyramids,

SEE SOME PICTURES

See the attached pictures. Please be aware the four "box" shaped wire stiffeners
are for mechanical convenience only. You can place as many as you like in arbitrary
positions down the length of the CAGE.

A dipole is deployed down the center-line of the cage. At the center of the dipole
install a radio listening device where the red letter 'O' appears.

HOW I BUILT IT

I used #10 bare copper wire from Home Depot. I made the CAGE an arbitrary length, about
30 inches (limited by mechanical constraints). I made the cross section of the CAGE square,
but I am sure that is not critical. I suspended a dipole along the centerline
by using monofilament fishing line for end insulators. I used an old Radio Shack VHF AM
aircraft radio reciever, which I kind of jam-fitted inside the cage. Instead you could use
the $80 SA for EMI testing. The sensing receiver must be an AM receiver, or a device that
shows signal amplitude. IT IS IMPERATIVE THAT THE DIPOLE AND SENSING RECEIVER ARE
COMPLETELY INSIDE THE CAGE WITH NO CONDUCTORS EXITING THE CAGE!!

HOW TO USE IT

To use it, tune the VHF receiver to a frequency that sounds like the interference
you are getting at HF. Grasp the CAGE at the middle, at hold it at shoulder level,
pointing front-and-back, with the receiver near your ear so you can hear the
offending signal and see the direction the CAGE is pointing.

To find a noise source, rotate the CAGE both in azimuth and elevation until you find a deep null.
The CAGE has EXTREMELY deep and sharp nulls off each end. So,When the null is found, the CAGE end is pointing directly at the noise source.

In another post I will provide the 4nec2 file I used to create the geometric images. The 4nec2 file may not be
valid for modeling; I just used it as a convenient 3d visual model.

73, Rod KM6SN


* v1.png (17.41 KB, 1280x1000 - viewed 384 times.)

* v2.png (22.79 KB, 1280x1000 - viewed 333 times.)

* v3.png (28.21 KB, 1280x1024 - viewed 339 times.)
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km6sn
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« Reply #1 on: October 16, 2020, 11:10:15 PM »

The attached file is a 4nec2 file. Change the .txt file extension to .NEC

This model is for visual illustration only. It may not be a legitimate electrical model.

73,
Rod

* villard.txt (1.33 KB - downloaded 136 times.)
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km6sn
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« Reply #2 on: October 16, 2020, 11:13:00 PM »

a fascinating read about Villard and early radio/electronics, including HP:

https://ethw.org/Oral-History:Oswald_Garrison_Villard
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Steve - K4HX
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« Reply #3 on: October 17, 2020, 12:24:09 PM »

Very interesting. Had read some of Villard's stuff in the past, but was not aware of this antenna. He worked at Stanford and SRI and had a lot to do with the development of over-the-horizon radar. Has also work with/for the legendary Fred Terman.
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WBear2GCR
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« Reply #4 on: October 17, 2020, 12:29:22 PM »

Curious - if there is no documentation on this antenna design, how did you come up with it??

Also where does one connect the antenna terminals of the receiver? ground to the cage, hot to
the center of the wire in the center?
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« Reply #5 on: October 17, 2020, 12:42:16 PM »

Interesting!  I've had a lot of luck locating RFI with a VHF-AM hand held scanner (aircraft band, for example) as those frequencies don't carry along power lines very far. A rapid increase in signal strength is truly an accurate indication of getting close.
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km6sn
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« Reply #6 on: October 17, 2020, 01:06:11 PM »

I found the description in an  obscure radio book somewhere over 30 years ago.

The noise receiver is connected to the dipole in standard fashion; install a center insulator and connect a feedline. I did not use a balun, but I did coil about 6 turns of the RG174 feedline to about a 1 1/2inch diameter. The receiver was placed at the  center of the dipole.

You can see an article about similar DF equipment here:

https://www.arrl.org/files/file/Technology/tis/info/pdf/9408033.pdf

The concept is similar, but a strikingly different implementation.
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« Reply #7 on: October 19, 2020, 05:09:55 PM »

Seems essentially the same as Fig 4...?
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Tom WA3KLR
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« Reply #8 on: October 19, 2020, 05:36:13 PM »

Hi Rod,

I looked through my books, the closest thing I found was this 'frame antenna' in 'Radio Receiver Design, Part 1' by K. R. Sturley, John Wiley and Sons, Inc., 1947; first published in 1943, Author's Preface dated August 1942.  The antenna construction is totally absent to me.

* frame ant1.pdf (931 KB - downloaded 148 times.)
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73 de Tom WA3KLR  AMI # 77   Amplitude Modulation - a force Now and for the Future!
km6sn
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« Reply #9 on: October 19, 2020, 06:38:46 PM »

Tom.
Very interesting article.  Thank you for digging it out.

I could not understand the frame antenna; did not see how to feed it.
From the diagram, the feed looks like PFM.
Also confusing to me was the notion of "number of turns". It is not
clear to me where the turns are, and how they are deployed.
Could the frame be essentially an axial-mode helix?

It appears to me the frame has maximum response end-on, with a broadside null.
Is that your understanding, as well? That pattern agrees with an axial-mode helix pattern.

If so, the frame antenna pattern is in stark contrast to the Villard cage.

Any thoughts on that?
 
Rod
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Tom WA3KLR
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« Reply #10 on: October 23, 2020, 04:08:17 PM »

Rod,

I don’t think the frame antenna is a helix.

Since your cage antenna came out in the tube days, its implementation wasn’t too practical. But for the last 40 years with good, small solid state receivers it has revived merit as you found.

The frame aerial is from chapter 3 on aerials. Section 3.3 is Types of Aerials. What is mentioned – the vertical aerial, the inverted L, the T aerial, the dipole aerial, and the frame aerial. I think it was a meager attempt to throw in something else also.

You’re right that the Villard cage has its null in-line with the cage and the frame loop has is peak in-line with the major axis of the loop.  It appears that the frame loop is unshielded, multi-turns allowed, close spaced, although the diagram does not show the feed, I am thinking it was fed at the end.  I believe it has to be tilted a bit.

The ‘Radio Receiver Design’ books by Sturley are interesting to browse through though. I own Part I.  I don’t think that Part II was as popular. Below are the books, available as pdfs:

Part I R.F. Amplification and Detection

http://www.tubebooks.org/Books/Atwood/Sturley%201943%20Radio%20Reciever%20Design%201.pdf

Part II – A.F. amplifiers, TV, and FM Receiver Design

http://www.tubebooks.org/Books/Atwood/Sturley%201943%20Radio%20Reciever%20Design%202.pdf

Diverging from the topic, another old radio book I have that I really like is ‘Short Waves’ circa 1930 which I mentioned in another thread previously.
I couldn't find a pdf of it on-line and it is probably rare.  It is full of great photographs.

http://amfone.net/Amforum/index.php?topic=8615.0
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73 de Tom WA3KLR  AMI # 77   Amplitude Modulation - a force Now and for the Future!
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