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Ordering on line

Discussion in 'Electrics UK' started by stem, 17 Apr 2019.

  1. Laurence Harvey

    Laurence Harvey

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    ...is the answer 42? :unsure:
     
  2. SUNRAY

    SUNRAY

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    are we talking about a front end, pi tank, 5/8ths whip etc or diameter?
     
  3. bernardgreen

    bernardgreen

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    Yes the answer could be 42 but for it to be 42 would require the invention of a new unit of length.


    Sunray is on the right wavelength............
     
  4. JohnW2

    JohnW2

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    Well, in the world I used to spend a lot of playing in, a "2 meter coil" would actually be a "144 MHz coil" (well, actually, a 144 Mc/s coil back then!) - or, more precisely, the coil of a 144 MHz tuned circuit .... and the 'coil' of a 144 MHz tuned circuit would be made of only a few inches of wire!

    Kind Regards, John
     
  5. JohnW2

    JohnW2

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    I can't add a pic by editing my previous post - so, here a "2m coil" which ""I made (nearly 55 years!) earlier" - with a bit of paper for clarity, and a 20p piece for scale.

    upload_2019-4-22_10-52-32.png

    Kind Regards, John
     
  6. bernardgreen

    bernardgreen

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    Thanks John, I was looking unsucessfully for an image to explain the answer,

    The good old days.......
     
  7. Laurence Harvey

    Laurence Harvey

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    Blimey, that resonates with me :D. My old college lecturer taught us this bonkers ‘resonant frequency’ mnemonic: “Down in the jungle having a look see,..1 over 2pi root LC” (y)
     
  8. JohnW2

    JohnW2

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    You're welcome.

    A "2 metre coil" is, of course, not necessarily a coil at all. What I posted before was the 'input' tuned circuit. If I turn the (dusty/rusty!) box over, you can see that the 'output' tuned circuit has a 'coil' which is not quite a single turn - just two copper rods, joined at the end ...

    upload_2019-4-22_12-4-19.png

    Indeed. It's nice/nostalgic to see a 1kΩ resistor which is big enough and with a light enough background to be able to read the 'rings' without struggling! The close-up photography, 50+ years on, does not say a lot for my soldering proficiency 'back then'!

    Kind Regards, John
     
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  10. JohnW2

    JohnW2

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    In context, the problem with that mnemonic is that, in relation to the first pic I posted, that there is no explicit "C", the capacitance of the tuned circuit just being the stray capacitance.

    In the second pic I've just posted, there is an explicit "C" (in addition to the stray capacitance), but it's just an improvised one (just two copper disks, one of which can be moved relative to the other) - so, without some calculations (which are unlikley to be very accurate!), one doesn't know the value of its capacitance!

    Kind Regards, John
     
  11. EddieM

    EddieM

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    What is it with resistors these days, do they print the band's on them in less definable colours, or is it just my eyesight, really struggle with them now :(
     
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  12. Laurence Harvey

    Laurence Harvey

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  13. Laurence Harvey

    Laurence Harvey

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    You’ve have to at least give me some credit for remembering that formula from my youth,...almost 2 centuries later :);...or perhaps it just feels that long ago. :eek:
     
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  14. JohnW2

    JohnW2

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    I recently asked exactly the same myself. I know that my eyesight is not what it was decades ago, but that's certainly not the entire answer.

    The resistors are, of course, generally a lot smaller than they used to be - which (from the point-of-view of 'reading' them) is not a good start. However, I think it's the actual colours they now use which is the main problem these days - coupled with the background colour. The ones (which are very common) that drive me most mad are those with dark blue backgrounds. With those, I often find it difficult (or impossible) to work out what colours the bands are meant to be.

    As I recently wrote, with resistors like that, these days I very often find myself reaching for my meter 'to check' (or even 'find out' in some cases!) the resistance - something I would never have had to do a few decades ago.

    Given that a high proportion of commercial/industrial assembly of electronic things is now done by 'robots', I wonder if the problem is that they are now prioritising 'machine readability', rather than 'human readability'?

    Kind Regards, John
     
  15. JohnW2

    JohnW2

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    Oh, sure, you get full credit.

    It's amazing how those things 'stick' in one's memory. I was initially educated in disciplines that were absolutely riddled with mnemonics (many/most of which {at least the 'student modifications' thereof} are not repeatable in front of a family audience!) - and I remember a fair proportion of them (and their meanings) ~50 years on.

    Indeed, I even remember some from before my uni education - like TWEGOLAPS (which was discussed here a while ago!), from my days in the cadet force at school :)

    Kind Regards, John
     
  16. EddieM

    EddieM

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    Good to know it's not just me, I'm used to the ones printed on a dark burgundy body, but I got some recently, where the body is light blue, I can't make head not tail of them. I've resorted to taking a photo of them and enlarging it, even then I can't really make out the colours properly.
     
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