• march 2017 update

    Bob Coggeshall • 03/10/2017 at 13:50 • 0 comments

    Current XD rev performing well. Software performs as CW beacon. There were some issues with parasitic RF swamping-out mic-in which was solved by not using a directly connected rubber ducky.. XE version of board will resolve this by isolating GND area under Dorji with inductors.

  • Next Revision

    Bob Coggeshall • 06/16/2016 at 13:37 • 0 comments

    NEXT VERSION

    Planning on a bit of a pivot. The 2nd version will be much simpler breakout board, making the design usable with any 3.3V microcontroller the user chooses:

    • DRA818[V,H] Transceiver module
    • Mini-circuits LPF
    • Voltage Divider for DRA's MIC in to interface with a 3.3V DAC
    • N-Ch MOSFET for 3.3V Logic to drive DRA's Push To Talk
    • LM358 OpAmp to boost DRA's AF Out to 0..3.3V range for microcontroller Analog In
    • 12V to 5VDC Voltage Regulator

  • First Version Board Revisions

    Bob Coggeshall • 06/16/2016 at 13:29 • 0 comments

    MODIFICATIONS

    The first version of the board was assembled and tested. A few modifications were required for full operation:

    • Push to Talk: The 3.3V MKR1000 was unable to drive PTT. An N-channel MOSFET was added
    • MKR1000 DAC Driving DRA's MIC IN : requires a 10:1 voltage divider
    • DRA AF OUT Driving MKR1000 Analog in: requires 2x amplification. An LM358 Op Amp was added

    CURRENT DRAW

    • On high-power setting, the DRA draws about 600ma off of the 5V rail

    BATTERY MANAGMENT

    • Management of the VBATT rail proved to be tricky. The LiPoly rail must not go below about 3.2V. The pack being used has protection, once it kicks in, output goes to 0V

  • Initial Design

    Bob Coggeshall • 04/24/2016 at 16:40 • 0 comments

    Basic requirements were established. DRA818 is a new one-of-a-kind VHF Ham transceiver on a chip. It needed to be combined with a capable applications processor and local communications capability. The Arduino MKR1000 was chosen as it provided a turn-key solution. Turn-around time for the initial prototype was minimized by using an all-module approach.