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Possibility of using prop for a 216-220 Mhz Beacon — Parallax Forums

Possibility of using prop for a 216-220 Mhz Beacon

James LongJames Long Posts: 1,181
edited 2008-11-03 19:46 in Propeller 1
Ok, I'm a bit lacking on transmitter knowledge, so I thought I would ask.

Could the propeller be used to transmit a repeating pulse on a frequency of 216-220 Mhz?

I would like to hear the ideas, and information about possible drift.

Thanks,

James L

Edited title for mis-spelled words

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James L
Partner/Designer

Lil Brother SMT Assembly Services

Post Edited (James Long) : 11/4/2008 12:29:52 AM GMT

Comments

  • LeonLeon Posts: 7,620
    edited 2008-11-03 15:24
    That would be illegal in most countries, without an appropriate license.

    Leon

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    Amateur radio callsign: G1HSM
    Suzuki SV1000S motorcycle
  • Mike GreenMike Green Posts: 23,101
    edited 2008-11-03 16:08
    No, not realistically.

    The cog counters can produce an output up to about 128MHz which could be doubled to the 216-220MHz range, but the output would have a lot of noise and would need a lot of cleaning up. The high frequency (and the frequency multiplication) also multiplies any drift.

    The Propeller's oscillator is not designed for any kind of temperature stability. Crystals drift with temperature changes, with changes in capacitive load. There would be changes with any shift in power supply voltage, etc.

    You would be much better off using an external oscillator designed for that frequency range and using the Propeller just to gate it on and off.
  • James LongJames Long Posts: 1,181
    edited 2008-11-03 18:48
    Leon said...
    That would be illegal in most countries, without an appropriate license.

    Leon

    Leon,

    This was being designed as a part 15 compliant device, and it would need to be tested for certification.

    James L

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    James L
    Partner/Designer

    Lil Brother SMT Assembly Services
  • James LongJames Long Posts: 1,181
    edited 2008-11-03 18:50
    Mike Green said...
    No, not realistically.

    The cog counters can produce an output up to about 128MHz which could be doubled to the 216-220MHz range, but the output would have a lot of noise and would need a lot of cleaning up. The high frequency (and the frequency multiplication) also multiplies any drift.

    The Propeller's oscillator is not designed for any kind of temperature stability. Crystals drift with temperature changes, with changes in capacitive load. There would be changes with any shift in power supply voltage, etc.

    You would be much better off using an external oscillator designed for that frequency range and using the Propeller just to gate it on and off.

    Thanks for the info Mike, I didn't think the accuracy of the propeller would do in this situation.

    I wonder if I could tune it down into the FM range....and keep the cost down. Would still need an external oscillator to prevent major drift.

    James L

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    James L
    Partner/Designer

    Lil Brother SMT Assembly Services
  • LeonLeon Posts: 7,620
    edited 2008-11-03 19:12
    An overtone crystal and a Butler oscillator followed by a multiplier will be fine at 200 MHz, and should meet the certification requirements if it is properly designed. The Propeller is overkill for this application, you just need something like a PIC or AVR to key it. Another option would be the Si Labs Si570, which has an I2C interface for setting the frequency.

    Leon

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Amateur radio callsign: G1HSM
    Suzuki SV1000S motorcycle

    Post Edited (Leon) : 11/3/2008 7:45:15 PM GMT
  • Mike GreenMike Green Posts: 23,101
    edited 2008-11-03 19:20
    You would need to have the clock frequency as a submultiple of the output frequency to minimize PLL noise (like a 54.5MHz system clock for a 109MHz cog counter output doubled to a 218MHz output). A 6.8125MHz temperature compensated crystal would work with PLL8X to provide this.
  • James LongJames Long Posts: 1,181
    edited 2008-11-03 19:46
    Leon said...
    An overtone crystal and a Butler oscillator followed by a multiplier will be fine at 200 MHz, and should meet the certification requirements if it is properly designed. The Propeller is overkill for this application, you just need something like a PIC or AVR to key it. Another option would be the Si Labs Si570, which has an I2C interface for setting the frequency.

    Leon

    I agree, the Prop is way overkill for this project, but this is only a possible part of the project, the other parts have been designed, and are actually independent.

    James L

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    James L
    Partner/Designer

    Lil Brother SMT Assembly Services
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