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Creating an RF Signal using analog methods

  1. Jan 26, 2014 #1
    How is this done. Been reading about sputtering and DC sputtering is extremely simple. However, i'm not very experienced with RF circuitry so understanding exactly how to design that circuit confuses me a bit. Been reading about RF circuits but to generate an RF signal every method I find uses DAC converters and is more suited for music then high voltage applications like this. I understand how the impedance matching unit works fairly well and they use variable vacuum capacitors to manage the high voltage.

    Given that the impedance matching unit is done with a simple L matching ciruit using analog components I imagine the power supply has to do with analog components also. My google fu isn't finding much. I know radio predates the digital transistor so exactly how using analog components do you create a radio signal and tune the frequency?
     
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  3. Jan 26, 2014 #2

    Simon Bridge

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    Surely you've looked for old-style radio transmitter circuits online?
     
  4. Jan 27, 2014 #3
    Yeah, I understand I need to amplify it and increase the frequency of the input signal. Looking into it I'm thinking one of the things confusing me is I saw a mosfet / transistor symbol in the circuit and it seems to correspond to a vacuum tube. Which I'm just realizing is the analog equivalent to the digital transistor. So that solves a bit of it. Now just need to figure out how to tune it and see if that is enough to get to 13.56 MHZ in one step. Though I might need a toroidal transformer as well to reach the desired voltage, but I have no idea how those are tuned either. Just that they are used for RF transformers.

    Is there another high power equivalent nowadays to the transistor or is the vacuum tube the only option? I still see people making vacuum capacitors but can't see anything about vacuum tubes in modern day stuff. So it has me questioning if that is what is actually used nowadays. Or if there is a more practical way then a vacuum tube to do it.
     
    Last edited: Jan 27, 2014
  5. Jan 27, 2014 #4

    sophiecentaur

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    I'm not sure what you mean by a "digital transistor". A transistor is, inherently, an analogue circuit element which needs to be driven appropriately to have discrete states.

    I think you are trying to leap into this subject with just not enough background knowledge. You introduce the idea of a toroidal transformer, out of nowhere. (??)
    There is no need to go digital for a project like this.
    If you want a source of 13MHz then you can probably buy a low cost signal generator (eBay) and you could also buy an amplifier to deliver sufficient power for whatever you want to do. If you want to DIY the project then you will need to start with some basic circuit theory and construction experience at lower frequencies. Otherwise you will not be able to know what is happening with any circuit you try to build. This is not a trivial task that you can do in an afternoon. (You may be able to find a helpful Radio Ham who lives nearby - some people like a challenge and, if the application is interesting enough, a hobbyist could be persuaded to get involved.

    The idea of sputtering is simple but do you have the vacuum equipment to do it with?
     
  6. Jan 27, 2014 #5

    Baluncore

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    Use a 13.56 MHZ crystal oscillator to drive an ex-amateur linear amplifier. That should give you between 500 W and 1 kW. How much power do you need?

    Alternatively, there are many diathermy units available on the 2nd hand market for the higher ISM bands such as 27MHz and 40.68 MHz. Typical power output is 5 kW. They are used for induction heating of metals and for dielectric heating in the plastics industries.
     
  7. Jan 27, 2014 #6
    Google this: "QRP"
    It will give you lots of hits from people who build low-power RF stuff from scratch, both discrete and integrated circuits. It sounds like you want to do very high power stuff, which is non-trivial.
     
  8. Jan 27, 2014 #7

    sophiecentaur

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    I think it's time to issue the PF Safety warning about dealing with high power levels and high voltages. Not so problematic when fed to an antenna but, when transformed to high voltages and used in non-standard gear, a potential for self harm.
     
  9. Jan 27, 2014 #8

    Simon Bridge

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    I think the question is still too vague and general for anyone to give good assistance.

    @ChaseRLewis:
    We have to assume some particular project, like you want to build a commercial-level AM radio transmitter maybe?

    DSE used to have a kitset FM radio microphone too - had a range of a few meters off a 1.5V battery.

    At the other end of the scale, ships at sea used to use spark-gap transmitters that could (reportedly) fry seaguls at close range. The Morse keys used to have big insulating skirts so the operator wouldn't accidentally touch the contacts.

    I was initially wondering if you just wanted to know the principles of analog RF generation - but you do seem to have a particular project in mind. What is it?

    If we know the purpose of the RF, we can direct you better to what sort of information you need to know.
     
  10. Jan 27, 2014 #9

    davenn

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    ChaseRLewis

    hi there,
    It appears as tho you have a bad misunderstanding of what digital and analog is

    Pretty much any transmitter from oscillator to final amplifier is an analog circuit
    what makes it a digital or analog transmitter is the modulation type applied to it

    just for an example .... here's a basic 3 transistor ANALOG FM transmitter

    attachment.php?attachmentid=66068&stc=1&d=1390874186.jpg

    here's a basic single transistor Colpitts Oscillator running at ~ 12MHz Also ANALOG

    attachment.php?attachmentid=66080&stc=1&d=1390894651.gif


    Dave

    EDIT ... got home and discovered the Colpitts osc diag wasnt there
     

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    Last edited: Jan 28, 2014
  11. Jan 27, 2014 #10

    Simon Bridge

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    For that matter you can buy RF transmitters in a chip - such devices usually have digital IO these days it seems.
    I have a feeling that is what OP wants to avoid.

    The 3 transistor circuit above would fit the bill - analog mic input and crank-cap tuning, the only arguably digital component is the switch - and so would many others circuits easily googleable so I still wonder what OP actually wants. You know - to narrow it down a bit?
     
  12. Jan 27, 2014 #11

    Baluncore

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    Are you just interested in RF transmitter design, or do you actually need to make an RF sputterer?
    Some idea of the magnitude of the application would be useful.
    Is it for one-off or production line use?
     
  13. Jan 28, 2014 #12

    sophiecentaur

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    As does Mr Dyson, with the "Digital Motor" in his cordless vacuum cleaner. Shockin'!
     
  14. Jan 28, 2014 #13

    davenn

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    hahaha We have Dyson vac's in Oz but I hadn't noticed the "Digital Motor" comment in the telecommercials, mind you I skip those ads pretty quickly. maybe I should have a listen and a laugh


    cheers
    Dave
     
  15. Jan 29, 2014 #14

    sophiecentaur

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    Quite ridiculous that you should be in the Antipodes. I thought I was conversing with someone just down the road. haha. Space and time travel.

    (Doesn't mean you're a bad person)
     
  16. Jan 29, 2014 #15

    Baluncore

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    All things are relative. For example, I think it quite ridiculous that sophiecentaur thought davenn was in England.

    I believe davenn, sophicentaur and baluncore are all geospatially located south of the Watford Gap. United we stand.

    Certainly not at cricket.

    It is only the forces of prejudice that prevent the web of optic fibre from causing the immediate collapse of our digital universe to singularity.

    No matter how strongly the web of optic fibre pulls us together, will prejudice always keep us apart?
     
  17. Jan 29, 2014 #16

    sophiecentaur

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    Do you think that, if I gave a good tug on my ethernet cable, all the PF members' computers would move a bit nearer the wall sockets?

    (I didn't like his comment about the cricket. But our girls are doing not too badly so yah boo. I never watch it aamof. Six nations is soon.)
     
  18. Jan 29, 2014 #17

    Baluncore

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    No. But knowing your interest in experimental physics and your appreciation of the PF, I believe you are ideally situated to carry out your proposed experiment. I am also convinced that it will be successful in better uniting the PF membership.
     
  19. Jan 29, 2014 #18

    sophiecentaur

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    . . . . . . . .Did you notice anything happen just then? My screen's gone blank. haha
     
  20. Jan 29, 2014 #19

    AlephZero

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    Of course it's a digital motor. At any instant in time, it's either "on" or "off" :biggrin:
     
  21. Jan 30, 2014 #20

    meBigGuy

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    It's off topic, but why can't a digitally controlled motor and driver module utilizing high frequency class D bridged drivers and processor control be termed a "digital motor". It's all ON-OFF with no "analog" drive. It certainly isn't classic analog.

    I don't know exactly how the dysan motor actually works, but it certainly looked cool on Charlie Rose the other day.

    Just asking.
     
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