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Author Topic: SLAC develops novel compact VLF antenna for communicating where radios fail  (Read 2563 times)

N8FNR

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Well this is interesting: https://phys.org/news/2019-04-slac-compact-antenna-radios.html

A new type of pocket-sized antenna, developed at the Department of Energy's SLAC National Accelerator Laboratory, could enable mobile communication in situations where conventional radios don't work, such as under water, through the ground and over very long distances through air. The device emits very low frequency (VLF) radiation with wavelengths of tens to hundreds of miles. These waves travel long distances beyond the horizon and can penetrate environments that would block radio waves with shorter wavelengths. While today's most powerful VLF technology requires gigantic emitters, this antenna is only four inches tall, so it could potentially be used for tasks that demand high mobility, including rescue and defense missions. 
"Our device is also hundreds of times more efficient and can transmit data faster than previous devices of comparable size," said SLAC's Mark Kemp, the project's principal investigator. "Its performance pushes the limits of what's technologically possible and puts portable VLF applications, like sending short text messages in challenging situations, within reach."
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KD0REQ

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looks like a big ceramic resonator (buzzer) in a metal cage, no details in the article I saw on Apple News, but I have a Useful Working Theory (tm) that the resonator generates RF by exciting the metal cage. not being a solid state theorist, it's probably wrong. be interesting to have an RF emission plot to look at, and some practical contact information. if they are measuring sound, not RF, it's not very useful to us.
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AK0B

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I also found it interesting.  However, a crystal generates physical vibrations and not sure how a 6 inch one could be used to excite even a metal cage -  lot of questions note they indicated a long range but did not give any details. 

Stan AK0B
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WA7SGS

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One has to wonder if very small antennas could be developed for HF transmission which would actually be effective?  Never in my wildest imagination did I think something like this kind of antenna would work on VLF frequencies. 
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WD8OQX

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If this were APRIL, I'd think this a GAG!!!
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AF5CC

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RE: SLAC develops novel compact VLF antenna for communicating where radios fail
« Reply #6 on: September 02, 2019, 05:15:35 PM »

Is Gotham making the antennas?  That could explain a lot.

73 John W5TD
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KM1H

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RE: SLAC develops novel compact VLF antenna for communicating where radios fail
« Reply #7 on: September 03, 2019, 11:12:27 AM »

Yeah, but Gotham vertical antennas actually worked if you ignored the ads and used a good radial field. I knew several down on LI NY in the 50's who did just that.

I was using a 40M dipole at about 15'  fed with 72 Ohm twin lead tied together at the rig, with NO ground, and even worked KH6IJ on the 80M Novice band with about 20W. I never bothered to model it in later years but it likely wasnt very pretty.

Carl
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KH6AQ

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WA8NVW

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RE: SLAC develops novel compact VLF antenna for communicating where radios fail
« Reply #9 on: September 03, 2019, 06:58:01 PM »

Sounds like it was pirated from research conducted by U S Bureau of Mines back in the 1970's and early 1980s for mine rescue teams.  Your tax dollars at work. 
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VK6HP

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RE: SLAC develops novel compact VLF antenna for communicating where radios fail
« Reply #10 on: September 04, 2019, 02:18:58 AM »

I don't see the need for the negativity.  The research is from a respectable group and is published in a very good, peer reviewed journal. The efficacy of electrically short dipoles and small loops has long been known but the matching complexity, and attendant losses, have been huge problems.  This work is a new way of feeding energy to a short dipole and, using the fairly well known technique of direct antenna modulation, simultaneously overcoming some of the issues arising from the inherently high Q of the acoustic resonator dipole. It's early days, but everything has a starting point.  

Another useful commentary is available at: https://physicstoday.scitation.org/do/10.1063/pt.6.1.20190530a/full/

LiNbO3 is of course very widely known and used in radio engineering, and the techniques for making resonators, couplers and other elements are robust.  My own graduate work, many years ago, used the material in dispersive delay lines to make phase coherent multi-channel spectrometers. The gravitational radiation community also use lots of the stuff, for the obvious application of converting mechanical strain to electrical signals.

Hopefully there are still amateurs who, wishing to be on the forefront of radio science, actively embrace new ideas.

73, Peter.
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W9IQ

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RE: SLAC develops novel compact VLF antenna for communicating where radios fail
« Reply #11 on: September 04, 2019, 05:39:42 AM »

What does seem odd is the statement that they haven't yet measured the far field directly. Given the simplicity of that exercise, I wonder if the announcement is a bit premature.

- Glenn W9IQ
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- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

VK6HP

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RE: SLAC develops novel compact VLF antenna for communicating where radios fail
« Reply #12 on: September 04, 2019, 06:27:06 AM »

Glenn

Yes, I would have done that, and as a reviewer I would have suggested it, even if only in the form of an indicative measurement to segue into the next paper.  However, I suspect that the group is of a strong physics bent and that their key interest was probing the fields around the radiator to establish the equivalence to a very short dipole.

I don't think it detracts much from an otherwise interesting first paper, overcoming substantial hurdles, and I look forward to a follow-up.

73, Peter.
« Last Edit: September 04, 2019, 06:29:52 AM by VK6HP »
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G8HQP

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RE: SLAC develops novel compact VLF antenna for communicating where radios fail
« Reply #13 on: September 06, 2019, 06:40:33 AM »

As I understand it, this antenna gets round the Chu-Wheeler limit by modulating the antenna as well as the signal. The C-H limit says that a compact antenna cannot be efficient, small and wide bandwidth - you can only choose two of these. What they have done is choose small and efficient, and then got around the narrow bandwidth limitation by modulating the tuning of the antenna. It is a dielectric antenna, not a metallic antenna, so the radiation comes not from conduction electrons being moved by currents but by bound electrons being displaced by a voltage.
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