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AM FM HD Radio with prop? — Parallax Forums

AM FM HD Radio with prop?

tonyp12tonyp12 Posts: 1,951
edited 2009-04-21 15:51 in Propeller 1
Just using minimal external items, no IC chips.

Would it be possible to digitize a AM/FM signal and play it back with prop.

This would be a good exercise in understanding AM/FM·Radio

Decompress HD (hybrid) maybe not be possible
as it's similar to MP3 and the prop may not have the horse power.

Comments

  • AleAle Posts: 2,363
    edited 2009-04-21 13:40
    What do you want to digitize... the modulated carrier or the audio after demodulation ? or after the intermediate frequency stages ?.
  • tonyp12tonyp12 Posts: 1,951
    edited 2009-04-21 13:43
    I guess modulated carrier.

    As few external component as possible, so the prop will handle all of the demodulation in software.
  • Oldbitcollector (Jeff)Oldbitcollector (Jeff) Posts: 8,091
    edited 2009-04-21 13:49
    I can't lay my hands on the thread, (Arrggg!) but didn't Phil do an
    AM radio receiver with the Propeller not long ago?

    Might be a helpful link if someone can lay hands on it.

    OBC

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  • virtuPICvirtuPIC Posts: 193
    edited 2009-04-21 14:13
    Yes, I remember an AM radio with only two or three passive components. I tried it at home - five miles from an AM station (720 kHz) at several ten kW power. It worked! However, I got no other station in a test of a few minutes.

    Actually I am wondering if the threshold of a prop input is precise enough to handle such small signals. microphone_to_headphone.spin delivers lots of noise on my demo board. Okay, in worst case you simply have to add a fast comparator.

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  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2009-04-21 14:25
    Here's the thread in question: http://forums.parallax.com/showthread.php?p=743002 It includes several RF preamp designs.

    For FM you would need an external downconverter, since the frequency band is much higher.

    -Phil
  • potatoheadpotatohead Posts: 10,261
    edited 2009-04-21 15:51
    HD Radio employs a propretary mp3 like codec. Specifically, it's a wavelet encoder with a perceptual filter (the mp3 part), combined with receiver side spectral replication. (kind of like mp3 pro)

    Compressed audio exists up to somewhere between 5Khz and 8Khz. Above that, spectral replication is used to convey those sounds.

    And that is why HD radio is more about the perception of high resolution, instead of actually being high resolution. Typical bitrates seen in real broadcasts range from 36Kbps (AM HD) to 96Kbps. (Most FM HD radio broadcasts)

    The actual HD radio broadcast rule making permits ANY codec to be used. They had to do this because of the public interest. Truth is, ALL HD broadcasts are done with the Ibiquity codec, and each receiver is a licensed work, payable to Ibiquity.

    If the codec were to be reverse engineered, the computational requirements are very high. That is why there are not yet any cheap, portable HD radios!!

    For a good overview of the tech, I wrote a paper on it, just as HD was beginning US broadcast trials. It can be found here: http://opengeek.blogspot.com/2005/03/hd-radio-thoughts-speculation-and.html

    IMHO, this is all off limits to the Prop I.

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