Embedding a SDR in FT-991A

Discussion in 'Software Defined Radio (SDR)' started by PY2RAF, Mar 19, 2019.

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  1. PY2RAF

    PY2RAF XML Subscriber QRZ Page

    Hello there, SDR fans!

    Just to let you guys know that I'm gathering more information / feedback on a post that I made in a different sub-forum here at QRZ: I'm working on a project to actually EMBED a RTL-SDR inside a FT-991A, without extra or external wires, all coming seamlessly from the same USB port.

    The thread link is at https://forums.qrz.com/index.php?th...r-in-ft-991a-need-rf-designers-review.650840/ and I'd love to hear from you!

    73s de PY2RAF.
  2. PY2RAF

    PY2RAF XML Subscriber QRZ Page


    We have reached the Beta Stage!! SDR & Panadapter are hooked in the radio and are working!!!! \o/

    So here are the details!!! Link to pictures on all entries. Used board Revision I.

    1. Board bravely soldered by Hugo Marçal (PY2UGO), even with wrong footprints (soldering 1206 in 0805 footprint is... hard.)
    2. After checking for shorts and visual inspection, hooked a few test points for initial voltage check.
    3. All wired up, and powered: Board is drawing 9.6 mA. Remember that no SDR drawing power at this moment, it is powered from the computer.
    4. Voltage regulators are all nominal: External power supply at 13.8V, 9V providing 8.8V (within 10%), 5V at 4.92V, 3.3V at 3.34V. \o/
    5. Some fun with voltage drop when the power supply is disconnected, just to see the regulation range of linear Regulators
    6. Where to tap (pardon the ugly solder) the 13.8V from the radio - right after a fuse. Used Breadboard Jumper Wire and connector to allow disconnection
    7. Tapping ground from a screw under the board
    8. The Panadapter wiring and with U.FL connectors attached to it. Notice the thermal pad below the panadapter, more for isolation than heat dissipation. Notice the yellow jumper, bridging 3.3V to the SCPON pad and the GPIO pad (so it will bias the AND gate and flip the RF switch)
    9. Another angle of the Panadapter board
    10. The board's back side, where it is powered. The blue wire is bridging the 13.8V to the "EN" (enable) pad, since this pad is slated to receive the EN signal from the USB hub (which is not yet done). And yes, I missed entirely a proper ground pad. Tackled in revision K and L (experimental).
    11. Here, the Panadapter and the SDR boards installed in the radio. The SDR is wrapped in copper tape (and I bought a tape that is too thin). Remember that the SDR is entirely stripped off its enclosure, USB and SMA port (and yup, I re-soldered the USB and the SMA connector, that was ugly right??).
      I stuffed a few thermal pads in SDR board prior to copper-wrapping it, in order to dissipate heat and avoid the copper tape to shorting components.
      I also have added a slice of thermal pad over the Panadapter board, which is where we feed 13.8V in order to avoid shorts (because there's a conductive cushion in the bottom cover, that goes over the SDR). The SDR is lodged over the flat cables, which act as a coil.
    12. And the FT-991A in its full glory, with the USB cable (which I want to get rid ASAP) leaving the radio. Needed a choke, because the external RF picked up by the cable caused the SDR to hang.
    13. Initial test receiving, straight off J1026 (disconnected the SCP unit). Notice the noise bands.
    14. Same signal, now passing through the panadapter board. At this point, it traversed the Panadapter but the radio was open and there were no copper wrapping
    15. Same signal - Now with the radio properly closed and all finished. Way quieter
    16. The same signal - now with proper RF gain levels (IMPORTANT!!!). Even better!
    17. São Paulo at dusk
    18. HDSDR .REG containing my configuration and tweaks
    A few videos:

    1. FT-991A Panadapter at-a- glance and functionality
    2. How to mitigate RF image
    3. FT-991A internal amplifier impact in HF band
    Well, that's all!!

    Next Steps.
    • Replace the radio's USB hub with a four-port hub
    • Wire it accordingly
    • Get rid of the external USB cable
    • Procure the board with the upcoming Revision M and its components, with corrected footprints, produce the new board and replace the current board (will take a couple of months).
    That's it!

    My best regards,

    - PY2RAF.
  3. G0GSR

    G0GSR Ham Member QRZ Page

    Check the USB chip used, it may already be a 4 port hub.
    PY2RAF likes this.
  4. PY2RAF

    PY2RAF XML Subscriber QRZ Page

    Hey there Frank! o/

    Thanks for the heads-up. I have checked my radio, and it features the 2512 version. Will have to be replaced.

    Great information that you provided here, I'm building a Wiki (Work in progress, bear with me https://github.com/rfrht/FT991A-PAT/wiki ) documenting the entire process and will add a note about that possibility (the radio having 2514).

    For completeness, the picture:

    Oh still while I'm here, there are a few gotchas that I found when operating in SSB this weekend, you have to set a offset when operating in SSB mode. Config:


    My best regards, 73s;

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