Novel Compact Antenna for VLF

Discussion in 'Amateur Radio News' started by AE4G, Apr 12, 2019.

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  1. W0AEW

    W0AEW Ham Member QRZ Page

    Then your crystal cracks.
     
  2. MKEMP

    MKEMP QRZ Member

    Hi All: I’m one of the authors of this study. I’m glad to see this topic is of interest and am very happy to answer questions about the technical part of the project.

    I can only speak for our research and not some of the popular articles out three (I’ve even noticed some of my “quotes” are skewed). Most of those are intended for a broad audience and might not go into the details that a specialist would appreciate. Also, as someone noted, in an attempt to broaden interest, sometimes the details go… wrong. Also, we are undertaking fundamental research, so we are not claiming a ruggedized, fieldable system.

    We are in the middle of this development program, and we have published measurements in the near field to estimate the dipole moment. If you would like to know more about the program’s goals, if you google “DARPA AMEBA BAA,” the original programs metrics will come up. We do have further measurements at range in various environments (some in the middle of a field with cow patties everywhere), but have not yet published.

    We are coming from the perspective of, "If we must make this transmitter portable (within strict specified SWaP constraints), what is the maximum efficiency achievable with a useable bandwidth?" We are still undergoing basic research, but end of program metrics are 100 fTrms @ 10 km. Also, to clarify, what might be qualified as “useful” for our sponsor won’t check all the boxes for the broad utility of VLF/LF.

    We are maximizing the system Qm to reduce losses in the transmitter. Our total Q is between 300,000-600,000 in laboratory demonstrations. We are using “direct antenna modulation” to demonstrate a bandwidth beyond the passive Bode-Fano limit. The use of piezoelectricity allows us to not need an external impedance matching network. We operate at the acoustic resonance.

    We are always looking for ways to improve our approach and of course are open to suggestions to increase the precision of our characterization. If there is a particular test or setup you guys might be interested in, I’d be happy to try it out. Next step for our program is increasing the power out by 10x and increasing the modulation depth. In phase 3, we increase power by another factor of 100x.

    Regards,

    Mark
     
    WR2E, KQ6XA, AE4G and 2 others like this.
  3. W0TDH

    W0TDH Ham Member QRZ Page

    Mark,

    I certainly am not any sort of Guru.....but, if this concept could be utilized as a receiving apparatus, tuned to one
    of the Earth's fundamental Freq's, that might be most interesting as well.
    Short range communications for trapped Miners and Mariners, most certainly would be of great value in rescue missions.
    73, Tom
     
  4. WB5WPA

    WB5WPA Ham Member QRZ Page

    re: "Well I strung up a end fed 9:1 bauln with 285 feet of wire as high as my trees, which are about 35 feet. I guess the Rx-Tx is ok - but id like to talk to anybody out of the 350 mile area.."

    What is distance Texas to Michigan? Over 1000 miles? Made regular sked with WW8II and others over that distance. Also, a group that meets on 1895 kHz in WI area in the mornings, 6 AM local on 160 meters. I have a lot less than 285 ft of wire, too.

    re: "Next ill try a vertical antenna for 160 - spirally wound."

    Good luck. When that 'fails to deliver' look up my bio page here on QRZ. One should try all losing solutions before finding 'the winner'. We had a guy down near San Antonio try that one, he was weak up here near Dallas compared to other stations down south here in Texas.
     
    Last edited: Apr 15, 2019 at 12:04 AM
  5. N2FVB

    N2FVB Ham Member QRZ Page

    A piezoelectric crystal driven at 30Khz will emit ultrasonic sound that should be easily detected by a similar crystal 100 feet away.
    Quite efficient? Yes. Send data? Sure! And you couldn't hear it.
    A piezo transducer in the VLF audio range could be deafening with enough power.
    How would it sound "thousands of miles beyond the horizon"?
    Probably not.
     
  6. MKEMP

    MKEMP QRZ Member

    A quick note: we are not sending sound. For many tests we have the piezo in vacuum. This is an electromagnetic transmitter.
     
  7. WD5JKO

    WD5JKO Ham Member QRZ Page

    Maybe we should introduce the term dbi, but here we rate the antenna gain in db referenced to an Isotron.;)
     
  8. W0IW

    W0IW Premium Subscriber QRZ Page

    It ,looks ,sounds like they are just copying off of Nickolas Tesla, but a smaller version
     
  9. W0IW

    W0IW Premium Subscriber QRZ Page

    .

    Hey guys
    ,looks ,sounds like they just copying off of Nickolas Tesla, but a smaller version
     
  10. AE4G

    AE4G Ham Member QRZ Page

    Hi Mark,

    Thanks for dropping by. It is great to have one of the authors engaging with us.

    If you don't know, below are the Amateur Radio allocations that may be the most compatible with the experimental device.

    - 2200 meter band: 135.7 - 137.8 kHz.
    - 630 meter band: 472 - 479 kHz.

    Power is limited to 1W EIRP (5W EIRP on the 630 meter band in some areas).

    With what you know so far about this method, do you think 1W EIRP may be feasible at some point? Do you yet have an idea of what the maximum radiated power may be for a similar device?​



     

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