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

    Hello there, QRZers! o/

    I'm working on a personal project to embed a SDR inside a FT-991A.
    This project is a hard hack on something that it was already being done. Check the vanilla instructions in https://c.rf01.co:8443/q/pat-70-ft-991a.pdf .
    I don't like the idea of drilling a hole in my radio's chassis. And I thought... What about if the radio had a SDR INSIDE it, and exported through its USB port, without hanging or extra wires, ports, etc.? THAT would be slick.

    After a full sunday brainstorming the idea, reading datasheets and using the radio schematic as a source for inspiration, I have come out with the schematic in https://c.rf01.co:8443/q/panadapter.pdf .

    So, this is obviously designed by someone without a degree in Electrical Engineering, and I have used the Radio's schematic as a source of inspiration for the decoupling and stuff.

    The part that I actually designed was the "Signal Control Board", where I have a AND port to bias a transistor which will actuate a solid-state analog switch, which will connect or not the RF signal from the radio's IF tap to the Buffer Board & SDR.

    Since this is going to be installed in a RF-harsh environment (inside a 100W transceiver, though not on the same board as the RF PA unit) AND, to make things worse, where the RF quietness is highly critical (this is actually close to the tuner stage), I was wanting to check with you guys:

    1. Is the Q1 & U2A in Signal control board correctly designed? I'm under the impression that I should have used a PNP here instead;
    2. Does the decoupling look sufficient?
    3. Any shielding suggestion/recommendation, etc.?
    4. In the original project, the PAT-70 IF input uses just a as-short-as-possible standard wire. What about using a co-ax?
    5. Any other ideas?

    Appreciate your awesomeness ;-)

    73s de PY2RAF.
  2. KA9JLM

    KA9JLM Ham Member QRZ Page

    Your drawing don't show how you are coupling to the IF. Or if it does I missed it. Looks like direct coupling. That will most likely Not work.

    I think that was one problem people had doing the mod.

    If Not done correctly, It kills the IF signal, Lowers it a bunch.

    Good Luck.
  3. PY2RAF

    PY2RAF XML Subscriber QRZ Page

  4. KA9JLM

    KA9JLM Ham Member QRZ Page

  5. PY2RAF

    PY2RAF XML Subscriber QRZ Page

    Okay, here it comes, Rev C -

    I was not entirely convinced that the transistor was actually well designed (well, it was NOT) but in the end, it was entirely disposable - The gate output is enough to flip the switch. Removed it.

    New PDF: https://c.rf01.co:8443/q/panadapter-rev-c.pdf


    - RF
    KA9JLM likes this.
  6. PY2RAF

    PY2RAF XML Subscriber QRZ Page

    Okay, here comes Revision D!

    Instead of reinventing the wheel, I reused OE2DOR's AWESOME and NEAT design and embedded my new logic over there.

    First Panadapter (PAT) design screenshots:
    Back: https://c.rf01.co:8443/q/ft-991a-pat-back-d.png
    Front: https://c.rf01.co:8443/q/ft-991a-pat-front-d.png
    Schematic: https://c.rf01.co:8443/q/ft-991a-pat-d.pdf

    The entire project connection overview:

    Comments, suggestions and most important, design flaws comments are welcome! ;-D

    73s de PY2RAF.
    W1TRY likes this.
  7. PY2RAF

    PY2RAF XML Subscriber QRZ Page

    And here it is.... Revision E!


    - Now sports a RF switch (PE4259) instead of a regular Analog switch (was: SN74LVC1G66);
    * Also contains its resistors as per reference design;
    - Changed voltage from 5V to 3.3V to Switch and AND port;
    - SDR output will be grounded by default when switch is in default state (RF 2 port) port
    - Updated list of contributors in Silk Screen.


    PCB Back: https://c.rf01.co:8443/q/ft-991a-pat-back-e.png
    PCB Front: https://c.rf01.co:8443/q/ft-991a-pat-front-e.png
    Schematic: https://c.rf01.co:8443/q/ft-991a-pat-e.pdf
    Overview: https://c.rf01.co:8443/q/panadapter-rev-e.pdf

    Appreciate your comment, review, criticism and suggestions!

    73s de PY2RAF.

    "given enough eyeballs, all bugs are shallow"
    - Linus Torvalds
  8. PY2RAF

    PY2RAF XML Subscriber QRZ Page

  9. PY2RAF

    PY2RAF XML Subscriber QRZ Page

    Reaching the 6th iteration, it is.... Revision F!


    * Added 1 nF capacitors in RF lines in PE4529 (except RF2, goes with a 470 pF to GND)
    * Got rid of the VCC via which was crossing the RF line (argh)
    * Finally got the courage to change a bit the board layout and escape from the thin strip that I was working previously.
    * And another THANK YOU to Gordon AD5GG for his invaluable feedback


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

    Appreciate your comment, review, criticism and suggestions!

    73s de PY2RAF.
    Last edited: Mar 27, 2019
    KA9JLM likes this.
  10. PY2RAF

    PY2RAF XML Subscriber QRZ Page

    Things are getting final, with a few refinements (and bug hunting). Revision G.


    * Removed a forgotten 1 nF capacitor
    * Implemented RF chokes in DC IN lines, as per Gordon AD5GG suggestion.


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

    Appreciate your comment, review, criticism and suggestions!

    73s de PY2RAF. \o \o

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