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NRG Pro5 TX

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  • Gareth Parker
    Here is a photo of my NRG Pro5 TX prototype. IÆm hoping to have this in production very soon. This new version uses an ôat frequencyö oscillator so there
    Message 1 of 3 , 26 Mar
    Here is a photo of my NRG Pro5 TX prototype. I’m hoping to have this in
    production very soon.

    This new version uses an “at frequency” oscillator so there is no ½ and 1½
    frequency harmonics to deal with and gives a very clean output, however on
    the other hand its susceptible to hum and RF feedback. The oscillator
    *must* be shielded from the rest of the board and especially from the power
    supply (not shown in this version), grounding and bypassing at RF is also
    very important.

    This prototype gives 5 watts across the entire band and uses a 2SC1971 for
    the output. Tuning is done by holding in the up/down push buttons for 3
    seconds then setting your frequency, there is no requirement to manually
    tune a trimmer capacitor and watch for lock output. The oscillator uses two
    varicaps, one for tuning and one for modulation. There is a hex 4049
    inverter which generates 30v to drive the tuning varicap, this allows for a
    wide tuning range and better stability with less noise. Ignore the red wire
    in bottom right corner of pcb, I forgot to run one of the traces to correct
    location.

    The PLL is a TSA5511 and is controlled over i2c using a pic 16F628A. The
    TSA5511 RF pickup is inductively coupled to the end of the oscillator coil.
    Charge pump current is increased during the tuning/locking stage, then
    reduced once locked for a very stable output and very little chance of the
    PLL trying to "correct" the base frequencies down at 30hz.

    No pre-emphasis is included with this design as there should *always* be
    some form of deviation control before the transmitter and this should be
    doing the pre-emphasis.

    Gareth
  • Ross Levis
    Can the power output be adjustable? This is required to be legal depending on the antenna gain and coax loss etc. From: LPFM_Radio@yahoogroups.com.au
    Message 2 of 3 , 26 Mar

      Can the power output be adjustable?  This is required to be legal depending on the antenna gain and coax loss etc.

       

      From: LPFM_Radio@yahoogroups.com.au [mailto:LPFM_Radio@yahoogroups.com.au]
      Sent: Sunday, 26 March 2017 10:28 p.m.
      To: LPFM_Radio@yahoogroups.com.au
      Subject: [LPFM] NRG Pro5 TX [1 Attachment]

       

       

      [Attachment(s) from Gareth Parker included below]

      Here is a photo of my NRG Pro5 TX prototype. I’m hoping to have this in
      production very soon.

      This new version uses an “at frequency” oscillator so there is no ½ and 1½
      frequency harmonics to deal with and gives a very clean output, however on
      the other hand its susceptible to hum and RF feedback. The oscillator
      *must* be shielded from the rest of the board and especially from the power
      supply (not shown in this version), grounding and bypassing at RF is also
      very important.

      This prototype gives 5 watts across the entire band and uses a 2SC1971 for
      the output. Tuning is done by holding in the up/down push buttons for 3
      seconds then setting your frequency, there is no requirement to manually
      tune a trimmer capacitor and watch for lock output. The oscillator uses two
      varicaps, one for tuning and one for modulation. There is a hex 4049
      inverter which generates 30v to drive the tuning varicap, this allows for a
      wide tuning range and better stability with less noise. Ignore the red wire
      in bottom right corner of pcb, I forgot to run one of the traces to correct
      location.

      The PLL is a TSA5511 and is controlled over i2c using a pic 16F628A. The
      TSA5511 RF pickup is inductively coupled to the end of the oscillator coil.
      Charge pump current is increased during the tuning/locking stage, then
      reduced once locked for a very stable output and very little chance of the
      PLL trying to "correct" the base frequencies down at 30hz.

      No pre-emphasis is included with this design as there should *always* be
      some form of deviation control before the transmitter and this should be
      doing the pre-emphasis.

      Gareth

    • Gareth Parker
      I have thought about that, and at this stage IÆm planning to vary the supply to the final two transistors hopefully without running into saturation problems
      Message 3 of 3 , 26 Mar

        I have thought about that, and at this stage I’m planning to vary the supply to the final two transistors hopefully without running into saturation problems in the driver stage.  The other option is to release two versions of this board with different matching in the output stages.

         

        I am still debugging the pic code also, I wrote this in hi-tech c using mplab.  Step size is 50khz, however for lpfm use I’m considering programming the pic to only allow selection of lpfm frequencies.  There will also be the option of a hard coded frequency which will allow removal of the lcd panel from the main pcb.  This may be useful for technical people who setup other stations but don’t want their customers tampering with gear etc… I know I’ve had a few of those, one guy I setup kept jumping across frequencies causing problems for everyone else.

         

        Gareth

         

        From: LPFM_Radio@yahoogroups.com.au [mailto:LPFM_Radio@yahoogroups.com.au]
        Sent: Monday, 27 March 2017 12:34 a.m.
        To: LPFM_Radio@yahoogroups.com.au
        Subject: RE: [LPFM] NRG Pro5 TX

         

         

        Can the power output be adjustable?  This is required to be legal depending on the antenna gain and coax loss etc.

         

        From: LPFM_Radio@yahoogroups.com.au [mailto:LPFM_Radio@yahoogroups.com.au]
        Sent: Sunday, 26 March 2017 10:28 p.m.
        To: LPFM_Radio@yahoogroups.com.au
        Subject: [LPFM] NRG Pro5 TX [1 Attachment]

         

         

        [Attachment(s) from Gareth Parker included below]

        Here is a photo of my NRG Pro5 TX prototype. I’m hoping to have this in
        production very soon.

        This new version uses an “at frequency” oscillator so there is no ½ and 1½
        frequency harmonics to deal with and gives a very clean output, however on
        the other hand its susceptible to hum and RF feedback. The oscillator
        *must* be shielded from the rest of the board and especially from the power
        supply (not shown in this version), grounding and bypassing at RF is also
        very important.

        This prototype gives 5 watts across the entire band and uses a 2SC1971 for
        the output. Tuning is done by holding in the up/down push buttons for 3
        seconds then setting your frequency, there is no requirement to manually
        tune a trimmer capacitor and watch for lock output. The oscillator uses two
        varicaps, one for tuning and one for modulation. There is a hex 4049
        inverter which generates 30v to drive the tuning varicap, this allows for a
        wide tuning range and better stability with less noise. Ignore the red wire
        in bottom right corner of pcb, I forgot to run one of the traces to correct
        location.

        The PLL is a TSA5511 and is controlled over i2c using a pic 16F628A. The
        TSA5511 RF pickup is inductively coupled to the end of the oscillator coil.
        Charge pump current is increased during the tuning/locking stage, then
        reduced once locked for a very stable output and very little chance of the
        PLL trying to "correct" the base frequencies down at 30hz.

        No pre-emphasis is included with this design as there should *always* be
        some form of deviation control before the transmitter and this should be
        doing the pre-emphasis.

        Gareth

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