Hard hack - Embedding a SDR in FT-991A - Need RF designers review

Discussion in 'Radio Circuits, Repair & Performance' started by PY2RAF, Mar 18, 2019.

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  1. PY2RAF

    PY2RAF XML Subscriber QRZ Page

    Seems that I have reached final! Sent the Gerbers for a quote. Ladies and Gentleman, this is Revision H.


    * Revised routes in Cheb Filter - Made the tracks fatter and straighter
    * Repositioned Q2 for better signal routing
    * Better unit spelling in silk screen for resistors
    * Flipped IF/SCP ports
    * A few routing changes.

    And the artifacts:

    PCB Back: https://c.rf01.co:8443/q/ft-991a-pat-back-h.png
    PCB Front: https://c.rf01.co:8443/q/ft-991a-pat-front-h.png
    Schematic: https://c.rf01.co:8443/q/ft-991a-pat-h.pdf
    Overview: https://c.rf01.co:8443/q/panadapter-rev-h.pdf
    Eagle Schematic, board and other details: https://github.com/rfrht/FT991A-PAT

    Would be delighted to hear from you!

    My best regards, 73s

    - PY2RAF.
    KA9JLM and W1TRY like this.
  2. PY2RAF

    PY2RAF XML Subscriber QRZ Page

  3. PY2RAF

    PY2RAF XML Subscriber QRZ Page

    I take it back!!!!!!!!!!

    That was far from final, how could I affirm that!! /o\

    This is now Revision I! _seem_ (I think, cough) to be done.

    * RTL-SDR USB port
    * U.FL jumper cords in BOM
    * 3 power regulators in the board
    * New CSV BOM file (suitable for Digikey)

    * Power supply: Now uses a single external 13.8V voltage source
    * Power routing

    * External final voltage jumpers
    * a stale parts.txt file

    All stuff, changelog, etc. in Github: https://github.com/rfrht/FT991A-PAT

    A side note: The current BOM is costing around $ 21 in Digikey.
    Last edited: Apr 8, 2019
  4. K7RJB

    K7RJB Ham Member QRZ Page

    Looking forward to installation instructions, pictures, board availability and total cost.
    PY2RAF likes this.
  5. PY2RAF

    PY2RAF XML Subscriber QRZ Page

    Hey there K7RJB o/

    I arrived last Saturday and got the stuff and did a few tests.

    There's a video and a few pictures in https://rf01.co:8443/q/pat-991a/

    So. A few notes.

    • Board costed $2 in jlpcb.com.
    • The parts costed $26 (though I bought the wrong SMA connector, how on earth is there a male pin in a normally female receptacle)
    • The SCPON signal is not the best option to the AND gate, along the RTL's GPIO port. SCPON is only HIGH when the Scope is being displayed. If you go to Menu or Setup, the SCPON goes down. Ah, if in Scope mode, it stays HIGH during TX as well (though I found no artifacts during 50W TX, I think the line is grounded somewhere else). For now since I have printed the PCB and etc, I will just bridge the GPIO port to both ports in the board. A next board revision will use TX9 signal plus a signal inverter (so TX high = signal low, TX low = signal high), so the AND gate will work accordingly.
    • IF signal is incredibly strong (centered in 68.450 MHz).
    • Seems that the footprints are correct
    • Definitely, the USB footprint was designed correctly, yay \o/
    • The SDR is a bit large for the radio, and I'm having a hard time finding a suitable place to lodge it (see picture 08)
    • I'm pending availability of the Tech for soldering the components and swapping the Main Unit IC
    Well, that's it!!! Super excited and looking forward to it!

    73s de PY2RAF.
    Last edited: May 14, 2019
    KA9JLM likes this.
  6. PY2RAF

    PY2RAF XML Subscriber QRZ Page

    Released Board Revision J!

    • Changed SCPON signal to RX9
      • Added a Voltage Divider
    • Added a few vias in large ground pads for voltage regulators
    • Moved USB port a bit back in PCB

    And guess what! it IS compatible with the vanilla FT-991!

    Project s Github (https://github.com/rfrht/FT991A-PAT) updated:
    • Now with instructions for FT-991 (non-A)
    • Updated BOM (some footprints were wrong; components were smaller; they can be soldered, but now with the right footprint & a weird Adafruit bad cable)
    • Added Gerber files (how could I forget to add it to the project)
    And I tip my hat (again) to Gordon AD5GG.

    Hope you enjoy!

    73s de PY2RAF.
  7. PY2RAF

    PY2RAF XML Subscriber QRZ Page

    Yet new release - Revision K (oh wow now I'm fearing running out of alphabet letters!)

    Changelog, for a tiring Sunday Night:

    19/May/2019 - Revision K
    • Changed footprints: BOM specifies 1206, project had 0805
      • Unified Resistors and Capacitors in 1206
      • Inductors are 0805
    • A few routing enhancements
    • Recalculated the component indexes
    • Updated BOM to reflect the new component index
      • And also found a unaccounted resistor, whoops.
      • Reviewed the entire BOM and circuits. Now everything should be fine.
    (famous last words those huh)

    Project's artifacts: https://github.com/rfrht/FT991A-PAT
  8. PY2RAF

    PY2RAF XML Subscriber QRZ Page

    Hello there, everyone!

    Seem that Revision K is gold!

    However, I got a few ideas and sharing with you guys, Revision L - in Experimental branch.

    • Added the ability to bypass entirely the amplifier and filters
      • Selectable by RF switch (default: off)
    • Added a 3-pole Chebyshev Band-pass Filter centered at 69.450 MHz, 3 MHz wide
      • Selectable by RF switch (default: off)
    • Revamped the Block Diagram
    • Added the BPF LT-SPICE simulation
    • Updated README, BOM, Gerbers and Pictures
    • And yes, board is getting somewhat cluttered.
    Github: https://github.com/rfrht/FT991A-PAT/tree/Experimental

    Block diagram:

    KA9JLM likes this.
  9. PY2RAF

    PY2RAF XML Subscriber QRZ Page

    Found a suitable SDR install site. Finally! It is far from tuning circuits and fits very nicely. It is the right side, with the red line. The panadapter board is outlined in yellow.

    I had to strip out the SDR case, because it was just too tall and prevented the bottom cover from closing the radio.

    When doing the final install, will add a thermal pad to both SDR sides and wrap it with copper tape in order to isolate potential SDR noise.

    So this is the install sketch. There will be another cable going out of the SDR, carrying the GPIO signals to control the Panadapter filters & Enable.

  10. 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.

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