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TX/RX on 108kHz need a lot of help.

  1. Oct 25, 2004 #1
    I’m wanting to first build a transmitter for 108kHz (later a reciever). I started by asking for a quote from a company for a custom made 108kHz crystal. Now they meantion that I need to give them the “load capacitance” before they cut it.

    So in one single request, I’ve already gotten way over my head - I’ve no idea what to do now. I don’t know what they’re talking about, or what numbers I can give without actually having a TX curcuit design in mind.

    Searching 108kHz on google brings up nothing about actually transmitting/recieving on that frequency... is there anyone here who could help me design these?
     
  2. jcsd
  3. Oct 25, 2004 #2

    chroot

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    By transmit, I assume you mean transmit via radio. 108 kHz is going to be very difficult to transmit, as it's extremely low. Why do you want to transmit on 108 kHz?

    The load capacitance is the capacitance of whatever circuit is connected to the crystal. You'd need to either estimate the value of whatever circuitry you're going to connect to it, or you need to pick a nominal value and then design the circuitry to approximate that nominal value.

    Getting a crystal custom-cut is an expensive business. Why are you doing this?

    - Warren
     
  4. Oct 25, 2004 #3
    Yes TX/RX via CW only (due to low frequency).

    So, as I thought, I’'ll need to design the circuit first and find out its capacitance before ordering the crystal?

    The price I was quoted was $104.58 and production time of six weeks. This is acceptable to me.

    I’m doing this as an extremely-long-distance communication experiment. Also wanting to test out different modified antenna designs for this frequency.
     
  5. Oct 26, 2004 #4

    chroot

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    What kind of transmitter design have you worked out so far? Maybe we can help you refine it.

    A $100 crystal... yikes.

    - Warren
     
  6. Oct 26, 2004 #5
    Well, since this was to be my first attempt at a transmitter, I was going to try something simple... something even I could understand from start:
    http://www.scitoys.com/scitoys/scitoys/radio/computer/computer_controlled_transmitter.html

    In fact, I’m quite embarassed on just how simple this example is, but I’m hoping to learn quick. An RF amplifier is also in my thoughts, but will come much later.
     
  7. Oct 26, 2004 #6

    chroot

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    Arctic Fox:

    I suggest you spend some more time educating yourself before attempting to build anything, particularly at 108 kHz. Radio Shack offers a number of good books for beginners.

    - Warren
     
  8. Oct 26, 2004 #7
    LOL! That’s why i’m posting here - to learn more. :D

    I am familiar with the employees and products of RatShak - I’ve no interest in them.

    What’s wrong with building something at 108kHz?
     
  9. Oct 26, 2004 #8

    chroot

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    As I've already said, RadioShack sells a couple of decent books on radio design. They are worth buying, even though the average Radio Shack employee doesn't know how to spell 'radio.'

    You should really look into joining a ham radio club in your area. The ARRL offers a number of fine books on beginner radio design, also.

    - Warren
     
  10. Oct 27, 2004 #9

    NoTime

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    I agree with chroot.
    Particuarly on joining a ham radio club.

    The club could help you avoid a visit from the MIB (in this case the FCC) should your project actually work :smile:
     
  11. Oct 27, 2004 #10
    I’ll have a look at RatShak again - maybe there’s something different I haven’t seen there (I used to work at one years ago).

    I hate to sound mean, but HAM operators have always been a problem for me. I’ve yet to find one who isn’t full of himself or self-righteous. I’ve also yet to find one who can think outside the box. If I was to meantion to them that I need to build a transmitter for 108kHz, like vomit they’d spew out every rule and regulation on the FCC and insist on my taking years out of my life to get (probably) a general-class permit before anything else. (read: blah blah, blah blah blah...)

    Who’s to say this transmitter is to be used in the US? As far as I’m concerned, the FCC, DOT, FBI, USSS, ABC, XYZ... have no bearing on this project. It’s a free experiment that will be done outside any red-taped borders. :)

    *calming down*
    Chroot, I will take a look at any ARRL books I find, as well as checking out RS. I feel it would be a lot easier to learn from people here as apposed to having to go out and search for info or learn from scratch...
     
  12. Oct 27, 2004 #11

    chroot

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    You're always within some government's borders -- unless you're in Antarctica, I guess -- so you are always obliged to obey that government's regulations. I wasn't really concerned with the legality of it.

    For the record, I got my general class license after studying Morse for approximately a week.

    So you just want to use CW? Just encoding information with the presence or absence of a carrier?

    - Warren
     
  13. Oct 27, 2004 #12
    LOL! You've got it - TX at the magnetic north pole with RX at the magnetic south. :biggrin:


    I thought about trying both - carrier on AM and no carrier on SSB. Is FM possible on this low of a frequency?
     
  14. Oct 27, 2004 #13

    chroot

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    I hope you're not serious. :frown:
    What kind of information are you planning on transmitting? You should pick your modulation based on that.

    - Warren
     
  15. Oct 29, 2004 #14
    I am. I’m wanting to see if the magnetic fields, Van Allen belts, or Auroras have any positive or negative effects on these frequencies and what effects they might be.



    I was thinking of just CW for person-to-person communications, but I’d be curious to see data through at that frequency; maybe start at 300baud and see how high it can go before complete failure.
     
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