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ON TOPIC ! A quick brain teaser.

Discussion in 'Electronic Design' started by Eeyore, Nov 6, 2006.

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  1. Eeyore

    Eeyore Guest

    The strain gauge thread reminded me of a product with an 'issue' I was once
    asked to take a look at.

    It was the receiver section of a marine radar.

    The detector was followed by several variable gain stages. These were wideband
    IC amplifiers made by Ferranti ( now Zetex ) with a control current / voltage
    that varied each IC's gain over about something like a 12-15dB range. The
    control ports were driven in parallel so that gain was swept equally between all
    the devices.

    They were at least 6 of these cascaded to provide the necessary gain before the
    signal went off for further processing.

    After the pulse was transmitted ( and the receiver input clamped ) the gain was
    ramped up with a triangle waveform to provide the necessary low gain for near
    targets and higher gain for distant targets.

    I took one look at the schematic, grinned and said I could fix it.

    What problems ( not less than 2 of them ) were they encountering ?

    Graham
     
  2. Let me guess, made in the U.S.A. ?
     
  3. Andrew Holme

    Andrew Holme Guest

    Was gain increasing as the 6th power of time? Could you improve the noise
    figure by running the first stage(s) at higher gain?
     
  4. J.A. Legris

    J.A. Legris Guest

    You've neglected to provide a vital piece of information (not counting
    the schematic) that you had that we do not: what was the complaint?
     
  5. Phil Allison

    Phil Allison Guest

    "J.A. Legris"


    ** Don't get sucked in.

    This is the silliest troll from the depressive bear in years.





    ........ Phil
     
  6. Tim Wescott

    Tim Wescott Guest

    1: Targets in the near range were coming through with a signal strength
    much less than expected (because the first amplifier(s) was saturating).

    2: I dunno, but I assume you'll illuminate us soon enough.

    --

    Tim Wescott
    Wescott Design Services
    http://www.wescottdesign.com

    Posting from Google? See http://cfaj.freeshell.org/google/

    "Applied Control Theory for Embedded Systems" came out in April.
    See details at http://www.wescottdesign.com/actfes/actfes.html
     
  7. Rich Grise

    Rich Grise Guest

    No way to tell - what was it not doing that it was supposed to be doing,
    and/or what was it doing that it wasn't supposed to do?

    Thanks,
    Rich
     
  8. Eeyore

    Eeyore Guest

    UK actually. Essex in fact.

    I also diagnosed the problem with the display for the same system after being
    woken up by the phone call.

    They didn't believe I could do it over the phone. That was a nice contract.

    Graham
     
  9. Eeyore

    Eeyore Guest

    Keep going. You're not quite there.

    Ideally, estimate the effect on the display.

    If you separate out all the effects there were 4 distinct ( inter-related )
    issues.

    Graahm
     
  10. Eeyore

    Eeyore Guest

    That's what I'm asking you to 'guess'. All the necessary info is there.

    Graham
     
  11. Eeyore

    Eeyore Guest

    LOL !

    It's a cute one.

    It took me only minutes to see the issues ( and the solution ) but I did have a
    display to view too.

    Graham
     
  12. Eeyore

    Eeyore Guest

    Keep going.

    A couple of you are on the right tracks but haven't yet got there.

    Graham
     
  13. Eeyore

    Eeyore Guest

    But there is. From first principles.

    It wasn't doing it as well as it should have.

    Imagine a classic radar display and how it's supposed to work.

    Graham
     
  14. DaveM

    DaveM Guest


    I'll bet that the gain ramp should have been a log ramp instead of a linear
    triangle.

    --
    Dave M
    MasonDG44 at comcast dot net (Just substitute the appropriate characters in the
    address)

    Some days you're the dog, some days the hydrant.
     
  15. Phil Allison

    Phil Allison Guest

    "Eeyore"

    ** It a FUCKING ASININE TROLL !!!


    - you ASD fucked pile of pommy shit .






    ........ Phil
     
  16. Eeyore

    Eeyore Guest

    Ok - so what was the fix then ?

    Graham
     
  17. Eeyore

    Eeyore Guest

    Keep going.

    Graham
     
  18. john jardine

    john jardine Guest

    Owz abouts, there's a forth power in the radar range equation. Yet the swept
    gain goes up as the 6th power. Distant objects look huge. ?

    Anyways, I changed to IDnet a month ago and if I can be arsed in
    persisting, it's now taking about 2 hours to connect. Did you have any
    problems?.
    john
     
  19. Eeyore

    Eeyore Guest

    If only it was that simple. You're on the right track of course but there's
    more.

    To 'connect' ???? What do you mean ?

    None at all. It was blisteringly fast at least initially. It may have slowed
    down a bit since. I'm synching at 8128/448 and it doesn't get any faster than
    that with BT's gear.

    http://www.adslguide.org.uk/tools/speedtest.asp
    Gives me 5464/378 kbps currentyl

    What are you coneecting with ? Details and stuff, router stats etc.....

    Graham
     
  20. Classic? A-scan, B-scan, or PPI?
     
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