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Lock me in, Scotty!

Discussion in 'Discussions, Opinions & Editorials' started by KL7AJ, Jan 5, 2013.

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  1. KL7AJ

    KL7AJ Ham Member

    So, how does one detect a radio signal >60 dB below the noise floor? Further, how does one do this without exotic digital signal processing?

    The traditional method for doing this is with the "Lock-In Amplifier" which is nothing more than a pair of direct conversion receivers operated in quadrature. The "binaural" I/Q receiver described a while back in QST is just such a beast...with one major difference.

    For such extreme low level signals, one must restrict the bandwidth, post-detection. Most lock-in methods work in the millihertz range....i.e, the "audio" bandwidth is .00i Hz or less.

    Of course, one can't receive very high data rates with such methods. So where does one use millihertz bandwidth receivers?

    At Hipas Observatory, we used the method extensively for detecting ELF signals generated by "pumping" the ionosphere with HF signals...the returns were generally in the 200 Hz range. We also used them for looking at Schumann resonances, which are naturally occurring ELF emanations excited by distant lightning strokes. Schumann resonance is at around 7-1/2 Hz, and is a good "test" signal for elf detection methods and equipment calibration.

    Lock-in methods will undoubtedly prove quite useful on our upcoming 630 meter allocation. It's an easy method to use and doesn't require any expensive hardware.

    Eric
     
  2. WB5WPA

    WB5WPA Ham Member

    Have you written any FORTRAN number-crunching apps that we can hack together under a GPL'd GUI so's we can have the same kinda fun?

    /mild humor

    Jim WB5WPA
     
  3. KL7AJ

    KL7AJ Ham Member

    Actually, FORTRAN is the engine under Octave. The latest version of Octave also uses GPL graphics!

    Eric
     
  4. WB5WPA

    WB5WPA Ham Member

    I was poking fun at WSPR and Joe T's work ... but I didn't know what was under the hood of Octave (nor had I ever looked!) ...

    Jim WB5WPA
     
  5. KL7AJ

    KL7AJ Ham Member

    WSPR is indeed amazing, but there will always be a place for top end analog methods....or in addition to!

    Stanford Research Systems builds a Lock-In amplifier with DSP. :)
     
  6. WB5WPA

    WB5WPA Ham Member

    Back to the question at hand ... have you cranked out any code that the greater (or lesser) amateur community can make some practical use of?

    Side Q: Are you close in any manner, way, shape or form to win/place/show on a Nobel prize (like Joe)?


    /all in jest don't ya know!


    Jim WB5WPA
     
  7. KL7AJ

    KL7AJ Ham Member

    I don't think I'm near a Nobel Prize, but maybe someone who reads Radio Science for the Radio Amateur WILL be. Then I can take some credit. :)
     
  8. KL7AJ

    KL7AJ Ham Member


    However...since you did ask (don't tell anyone)...I'm working (under the radar) with the FlexRadio folks on a pet project. I got to meet them at Dayton last year, and thought of a whole bunch of scientific applications for FlexRadios. They are ready made for a lot of the ideas I have. In fact, one of the fellers has a very similar background to mine....lots of ionospheric research and such.

    Eric
     
  9. WB5WPA

    WB5WPA Ham Member

    Does the project involve more than just one pair of I-Q channels at a time?
     
  10. KL7AJ

    KL7AJ Ham Member

    Yes it does....and the fact that you ask tells me you already know what I'm thinking. :) You are sworn to secrecy!
     
  11. WB5WPA

    WB5WPA Ham Member

    Better make the entire site ... :eek:
     
  12. KL7AJ

    KL7AJ Ham Member

    Nahh....95% of hams probably wouldn't give a rip. :)
     
  13. WB5WPA

    WB5WPA Ham Member

    Its the balance (the remaining 5 pct) that one would have to worry about (landsharks anyone?) ... but not seriously. I would not, of course, include myself in that balance, so, please, the juicy details; hold nothing back ... :D :D :D
     
  14. KL7AJ

    KL7AJ Ham Member

    You'll have to read Radio Science for the Radio Amateur. It comes out next month. :) I describe all the juicy deteils therein.
     
  15. WB5WPA

    WB5WPA Ham Member

    Which means ... you probably have a pre-release copy and certainly the manuscript as they used to say: "in hand". Faxing is so last century, but if you have a pdf copy ... :)


    On a more serious note, you have whet some appetites here.


    Jim WB5WPA
     
  16. K8ERV

    K8ERV Ham Member

    Minus 60 dB? No problem, I just crank up the volume control.

    TOM K8ERV Montrose Colo
     
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