Radio transmission from Pyra

Discussion in 'General Discussions' started by Silent-Hunter, Feb 27, 2019.

  1. Silent-Hunter

    Silent-Hunter Hardcore Member

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  2. ò.Ó

    ò.Ó Member

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  3. levi

    levi Still fresh, damnit!

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    If you scroll down past the pictures to the bottom of the first table, you can see that they tested hooking it up to a USB2 host. A USB3 host is not required, although I don't know if you'd be able to transmit decent FM at only 14MSps. I make the nyquist rate of a 90MHz FM signal to be 180MSps, so I guess we're looking at medium wave there at best really.
     
  4. Silent-Hunter

    Silent-Hunter Hardcore Member

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    I wonder if the PiTx can be ported though, that does AM. I prefer that in cars, stereo sounds weird in cars to me. I'll have a look though!
     
  5. ingoreis

    ingoreis Advanced Member

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    What?
    Pyra has a Build In FM Transmitter?
    Cool Feature :D
     
  6. levi

    levi Still fresh, damnit!

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    No, you'd need towards the cheapest end to plug in a usb->vga adaptor and VGA cable. If there's a spare gpio or something, you might be able to attach a simple wire to that, but I'm not sure what sort of dipole length you need offhand for FM, and fitting that inside the case might be tricky.
     
  7. ingoreis

    ingoreis Advanced Member

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    Ah i see..okay than its more Easy to use an external FM Transmitter when i need that.
    ....or Bluetooth :)

    But a nice Idea.
    Thank you for explaining that.
     
  8. Silent-Hunter

    Silent-Hunter Hardcore Member

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    It might not even need an antenna if it's close enough to the radio! I know the one on the RPi doesn't need an antenna.
     
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  9. dTal

    dTal Still Fresh

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    You don't want to do this anyway, at least not without a lowpass filter on your antenna. It's a neat demo, but because you're modulating a square wave (pin on/off) it vomits harmonics all over the spectrum. If the power is large enough to be practically useful in the frequency you want, it's also large enough to cause a huge amount of noise in every odd multiple of that frequency.

    For the same reason, AM (amplitude modulation) is impossible without further circuitry. You can't generate a sine wave carrier signal, or modulate the amplitude of the wave you do generate. You could possibly do it with a lowpass filter again, by using PWM to approximate the analog signal (the same trick used to do things like make disk drive stepper motors play music - in this case the ear acts as the lowpass filter).
     
  10. Silent-Hunter

    Silent-Hunter Hardcore Member

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    Well ideally, I'd like something I can plug into the USB port and drape the wire across the dashboard of the car, near the antenna. But I just got one of those bluetooth FM repeater thingies. But this would still be neat to be able to play music from the Pyra on any radio. I might have to build something I can plug into it. With a filter, of course.
     
  11. Grench

    Grench Forum Addict!

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    https://www.canakit.com/usb-fm-transmitter-kit-ux300-ux300-ca-ux300-ex.html
     
  12. Silent-Hunter

    Silent-Hunter Hardcore Member

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    Unfortunately that's a bit big, and their site is broken so there doesn't appear to be a way to buy one, or even see how much it costs.
     
  13. Grench

    Grench Forum Addict!

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    I'm under the assumption that for some reason you would rather have a device that plugs into a Pyra then transmits FM to the radio instead of just using a Bluetooth - FM re-transmitter.

    How about this one that skips the USB and goes straight out of the headphone jack?
    Code:
    https://www.amazon.com/JETech-Wireless-Transmitter-Phones-Charger/dp/B01HXQYDH4
     
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  14. Silent-Hunter

    Silent-Hunter Hardcore Member

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    Well if it's going to plug into the car, I'd rather it be bluetooth. What I'm looking for is something that lets me basically use radios as speakers. So if I'm over at my aunt's for example I can play music from her radio without plugging anything into it. I gave up on the car thing already, and bought an FM thing.
     
  15. klapse

    klapse Central Scrutinizer

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    Eh what? I thought the heads were moving at the same frequency as whatever was in the source signal they were playing.
    --- Double Post Merged, Mar 1, 2019, Original Post Date: Mar 1, 2019 ---
    Quite sensible imo.
     
  16. ò.Ó

    ò.Ó Member

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  17. Silent-Hunter

    Silent-Hunter Hardcore Member

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