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Alternator RF

Discussion in 'Home Brew' started by Dolmetsch, Jan 19, 2011.

  1. Dolmetsch

    Dolmetsch Member

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    So I was thinking. You see I live in two worlds. Ham Radio and Drag Racing. I was thinking about early spark transmitters and why they were so dirty. Tig welders are too as they use the same technology or did 20 years ago. I was thinking about mechanical/electrical signal generation and the early days of Radio. Alternators were actually used but bandwidth was wide, probably because motor speed was not real controllable and the lack of a filter /tank circuit. That is not the case now. In a race engine we must have perfectly timed spark. In some case there is no room for error or all goes kaput. I did some quick math. I can make with what I have on hand, buying nothing, 8 times 20,000 cycles (ok Herz) Very low level powerwise. Almost any freq could be generated with a bit of ingenuity and if speed of the ELECTRIC motor can be held with in very narrow as near perfect as possible speed then it would be possible to mech/electrically generate a useable and clean Rf signal. With a proper tank circuit who knows. WHY?
    Now that is the $64 question.
    Don VE3LYX


     

  2. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    Any RF signal produced by any type of spark transmitter will be quite wideband Even a spark generated from a DC source can be heard all over the band. I'm not sure you could ever have a tank circuit narrow enough to filter it properly as even the old spark transmitters had a crude tuned circuit on the output.
     
  3. Dolmetsch

    Dolmetsch Member

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    spark transmitter ?
    I said "alternator" not spark. Spark is hopelssy dirty but an alternator produces an sinewave signal. Some electronic distributors also actually produce AC in the primary circuit. (In the distributor inself before it goes to the ign module and ign coil. Car alternators also prduce AC. Remove the rectifier bridge and you have pure AC .At high speed say 6000 rpm an alternator may be turning 15000 rpm (pulley is much smaller so speed is higher)with three phases =45KC (With three phases or three complete cycles per revolution.) Anyway tis to me an interesting thing. Someday when I am in the shop I may try it at the millivolt level to see. Still have my scope too so i can monitor it.
    Don VE3LYX
     
  4. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    I'm sorry. When you said you were thinking about spark transmitters I misunderstood you and thought you were thinking about spark transmitters. :whistle:

    Spark transmitters were fed from high frequency AC alternators to begin with. Are you thinking about coupling the output of a high frequency alternator directly to an antenna system via a tank circuit of some kind? If the motor speed was tightly controlled and the speed high enough you could generate some radiated RF but I doubt you could get it high enough to be in any ham band.
     
  5. W5LZ

    W5LZ Crotchety Old Bastard

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    Try a square wave generator! You could certainly get in the right frequency range, but oh my, would it be 'dirty'! Talking through someone's toaster isn't exactly impossible, but not exactly very desirable either. :)
    - 'Doc

    (The frequencies you can 'get to' with mechanical alternators/generators isn't ever going to be very high. That's why the typical frequency of use with those spark-gap transmitters was so very low.)
     
  6. T23

    T23 Active Member

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    Hey, look up a "Rotary Spark Gap Transmitter", if you look it up on google you can see one in use with someone running morse on it, very interesting to watch...

    Its exactly what your looking to do with a motor.


    T23
     
  7. Dolmetsch

    Dolmetsch Member

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    YEs CK that is what I was thinking. I dont think it would be dirty. I believe a spark is because it is unpredicable as to the exact moment. An Alternator isnt unpredicable. All our north american ac clocks for instance are synched in the power grid. if you use a Euro Ac clock here aside from the 220 it wuld lose I think it is a minute and a half or so each day because of the 50 vrs 60 cycle. So minute ac motor control we already have in some form. Nowadays even DC motor speeds can be well controlled I suspect. Powerwise suppose we used say a 35 Amp 3 phase alternator at 6000 RPM . Lots of power there. And a 100 amp alternator ?!
    I however think I will start with a magnetic reluctor type distributor I have in the shop. I will hook it to my Scope and make sure it generates a good sine wave. I should be able to tell also by the pattern stablity on the scope if it can be driven at a well controlled speed (I will use my lathe to drive it.) as the pattern will march if it is varying. Power will be pea power at best. How far I will go with this I dont know. It just seemed to me the possibilty that what was impractical bandwidth wise 100 years ago is now possible. Just curious I guess. It is what gets me up each day.
    Don VE3LYX
     
  8. Captain Kilowatt

    Captain Kilowatt Professional Amateur
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    May I recommend that you do NOT touch the antenna when the key is down? :D
     
  9. Dolmetsch

    Dolmetsch Member

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    I promise.
    This might work on LF . I was also thinking since I have a scope with inductive or capacitive pickup capabilty I can get some patterns. I have also an old tig welder maybe 40 years old that is if I understand correctly actually a spark gap Hf unit. HF in welding being a relative term meaning more than 60 cycles or higher rather than specifcally High Frequency. Since nether device will be hooked to an antenna but just in the shop running I could do a scope pattern on the tig with the inductive pickup and then on the mini alternator aka magnetic reluctor type distributor. I think it would be obvious instantly why spark gap transmitters are illegal but I am thinking the little alternator will be pretty stable well spaced clean symetrical pattern. If I get time we shall see. I dont think the scope has been lit since I retired in 1997. It is a pretty good unit though designed to read even fuel injector pulses without a direct connection so it is very flexible for output types and amplitude. When I used my scope even then I knew I was the last of a dying breed! Now they refer to me as the dynasoar
    Don VE3LYX
     
    #9 Dolmetsch, Jan 21, 2011
    Last edited: Jan 21, 2011
  10. Dolmetsch

    Dolmetsch Member

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    Alexanderson alternator Data ";

    Check this out! I am too late. The last Rf alternator radio station went off the air in Sweden , are you ready? in 1996.
    Don VE3LYX
    Decided to do a "RF alternator" search
     

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