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Is there any particular reason this won't work? Thanks

Discussion in 'General Electronics Discussion' started by Bluepoint SEO, Oct 7, 2016.

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  1. Bluepoint SEO

    Bluepoint SEO

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    diagram.png
    If the components of the correct values of course. Thanks guys.
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    R4 is possibly on the wrong side of the capacitor.
     
  3. Bluepoint SEO

    Bluepoint SEO

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    Nope :'(
     
  4. Minder

    Minder

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    If so, How is the base biased?
    M.
     
  5. duke37

    duke37

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    R2 is also wrong.
     
    davenn likes this.
  6. Arouse1973

    Arouse1973 Adam

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    What is it? How does it work?
    Adam
     
    (*steve*) likes this.
  7. dorke

    dorke

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    Looks like you are trying to build a two stage 5Mhz RF transmitter.
    If that is indeed what you are trying to do,it will not work.

    As said above:
    1.No bias for the transistors.

    Plus:
    2.R1,R3 values very high,should probably incorporate RF chocks.
    3. No tuning for transformer T1/T2.
    4. No antenna matching circuit.
    5.No input matching circuit.
     
    Last edited: Oct 8, 2016
  8. Kabelsalat

    Kabelsalat

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    The thing about having no bias is that the signal that the transistor see, Vbe would swing somewhere between 0V and 0.7V, and if the singnal peak voltage never exceeds 0.1V, then the transistor would never get to the point where Ik changes. That is - signal never goes past this point.
     
  9. Bluepoint SEO

    Bluepoint SEO

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    Okay sorry guys on one of my weekend missions and from what little I know so far and have heard from other members here (and now you may laugh) with the feedback coming from the transistors (of 100k) to the base from the collector I thought they 'self' biased? Actually that's differ net piece of information I read on another website or perhaps on this thread (use 47k to 100k perhaps rings a bell). I know I can get told off for this for not researching but Adam - a) partly your fault for telling me about LT Spice ;-) :D and b) Minder: when I said 'nope' I meant nope tried it in which I did x 2 for R2 & R4 thanks Minder, Steve and Dike37 also.

    I lost once again my book on electronics book that goes into more detail about how transistors function, I'm gutted but I have 27 days to pick it up at least before it's destroyed. I left it somewhere along with my bag which is at the local(ish) police station (they found it fewwww). Local is miles away in Wales.

    I will tell you the truth being quite new to this and please correct me. Current downhill direction is from negative to positive, so in the case of a transistor it goes though the emitter where the base signal is switching the transistor on and off generating an AC signal [again if I'm wrong here] E<sub>v</sub> to B<sub>e</sub> high and low constantly to make the signal amplitude larger on the collector? The resistor on the collector of the transistor (either one of the 1K on my design) is to dissipate any surplus power (product of V and I)?

    And Adam, finally - I'm trying to modulate my mobile phone stored music out to the first transistor to be amplified somewhat before it goes to the transformer. I was expecting the transformer (eBay job from Hong Kong so can't understand the writing) from 12V to go to any voltage higher for a good transmission through a 1.59... MHz tank circuit before it got to the aerial which is 30cm long from the collector of the final Q2 transistor. I worked out (don't pay attention to that diagram's tank circuit) 1mH and 10pF should create 1.59Mhz which I'd honestly thought my radio would have picked up? Maybe I'm not doing something right - in fact I'm not!

    All in all tolerance, parasitic (I think I've heard it coined) component tendencies... I can't find a problem voltmeter checks anall. Except (I tried on 2 transoformers in total)

    My transformer (240v to 12v) which is an audio one looks like this:

    -----red[|]blue--------
    [|]yellow-----
    -----red[|]blue--------

    So has 2 reds going in, or maybe out, and 2 blues with a yellow wire coming out of the other side.

    I'e tried so many combinations I've just had no output on either side when I attach the 12v terminals.

    Perhaps I don't need this for the circuit though I have tried.

    Adam, anyone - books for a dumb yet passionate person on the web ISBNs welcome thank you?

    Any help or questions much appreciated.

    Thanks
     
  10. Bluepoint SEO

    Bluepoint SEO

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    Hi guys, was writing that previous before you posted but let me read what you've said thanks.
     
  11. Bluepoint SEO

    Bluepoint SEO

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    Jul 28, 2016
    Hi Dorke, thank you but these questions: What's an RF Choke. Lower values for the 1k caps (1 k has been my magic number for electronics so far). 3, 4 and 5 I can learn about these. Am I right saying a choke is an inductor?
     
  12. Bluepoint SEO

    Bluepoint SEO

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    Sabelvat; can I confirm this then from what information I've gathered: 0.7v is typically a transistors point of either on or off through a base from emitter to collector?
     
  13. Bluepoint SEO

    Bluepoint SEO

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    Adam, also how I imagined it should work (I know it's a science but it's okay to be creative sometimes I guess when learning). Q1 amplifies the signal from the input device (mobile headphone jack) and this in turn is run through a transformer to create larger amplitude (in terms of voltage [if I'm correct saying that (voltage at the cost of current right?)]) which is overlay on on to a 1.59 MHz frequency from a tank circuit (1mH and 10pF in parallel), the frequency then propagates to the aerial on the collector and is transmitted as electro magnetic frequencies? As for oscillator feed back to keep it going, am I right in saying this gets its energy from the collector of Q2 to keep on burning?

    Thanks Adam and everyone else - I'm going to have a read up on some biasing basics now.
     
    Arouse1973 likes this.
  14. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    In the case of R4, there's a cap in the way so that won't work (same for R2).

    There is very unlikely to be a single fault given your level of knowledge.

    Electrons flow that way, but by convention we assume the opposite. This also means that all the arrows point in the right direction :)

    You really need to try not to design your own RF circuits. You're using inappropriate parts and circuits which almost certainly won't function like you expect.

    Perhaps start by finding a circuit that does work?

    That's about as sensible as using red wire because the colour has been lucky for you so far.

    It's way more complex than that. Whilst it's true that the voltage controls the transistor, because it is part of a forward biased junction you must have a mechanism of allowing current to flow. There is a relationship between the BE voltage and the BE current.
     
  15. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Maybe start a few chapters earlier than that...
     
    Arouse1973 likes this.
  16. Bluepoint SEO

    Bluepoint SEO

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    Okay this is all good stuff thank you Steve.

    Red wire is lucky for me Steve ;-) Hmmm, any recommendations from experience on circuits that do work please? Without extravagant parts as the few I've tried from Google are just a) not working b) I'm not doing it right c) gremlins are tricking me.

    I've used a 27MHz crystal (with earth, positive and aerial pins) to play back stuff on my radio in my room I think I could only pick up at around 108MHz though. The problem is I really want to learn and I've never felt comfortable unless I know the guts of the system starting with the basics of course!

    I clocked and changed the caps R2 and R4 to no avail thanks :)

    Right can you help me then Steve think of something useful to do with a tank circuit other than watching a flashing light please?

    I have these coils in ranges of values but they're like oversized transistors, sure they work though mind?

    I don't know why but oscillations seem so important to me.

    Thanks Steve
     
  17. Bluepoint SEO

    Bluepoint SEO

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    What I learn is blogged Steve: electronics-blog.bluepointseo.co.uk

    It's a forever work in progress feel free to comment.

    Cheers
     
  18. Bluepoint SEO

    Bluepoint SEO

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    Not been with it lately though illness in the family etc.. What chapter do you suggest I start at by the way? What topic?
     
  19. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    I see nothing on your blog about capacitors.

    And the first page on transistors is riddled with misconceptions.
     
  20. Bluepoint SEO

    Bluepoint SEO

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    Hi Steve, yeah it's a work in progress when and as I get time. I do know capacitors block DC and allow AC depending on the frequency. These are all things I'm learning. Please ignore the transistor section as I think I state that's something I'll get around too.
     
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