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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

    P.s.: My boards and digi-key parts are still on their way, so you are way ahead of me @KC3LNW
     
    K3DDT likes this.
  2. K3DDT

    K3DDT Ham Member QRZ Page

    PY2RAF,

    Your response was quite detailed and you cleared up many of my questions. Again many thanks. I think I need a little more clarification.

    One more new question that I didn't realize yesterday. There is a pad on the Revision-O board near the mounting screw labeled "DIS" Is there any wire connected to this Pad? If so which one?

    I still need to order a simple bread board and probes from Amazon to setup a test bed so I'm probably a few days away from finishing the install. I'll keep you posted with my progress. Wish me success.

    Regards,

    John
    KC3LNW
     
  3. PY2RAF

    PY2RAF XML Subscriber QRZ Page

    Hey John! o/

    Your response was quite detailed and you cleared up many of my questions. Again many thanks. I think I need a little more clarification.
    Alright, here we go!!!

    A1) SO. Previously, the board was **disabled by default** (the first RF switch was putting the IF port to reflect and connecting Ground & SDR in). This now have changed.
    In revision O, the board is ON BY DEFAULT, meaning, the if port conduct to SDR in. Now, it will change to IF Reflect/ Connect Ground & SDR IN in the event of the TX9 signal (notice here, big change!) **OR** a GPIO command.

    So now GPIO Pin 32 is no longer connected to the PAT in Revision-O?
    GPIO32 is now the DIS (disable) signal - If you pull GPIO 32 to high to DIS pad, you will flip the RF switch to turn off the IF tap.
    So take the flow:
    TX9 signal;
    DIS GPIO signal;
    Then, "OR" logic IC
    ---> If any of them are true, switch first RF switch to reflect the IF signal and stop tapping it.

    One more new question that I didn't realize yesterday. There is a pad on the Revision-O board near the mounting screw labeled "DIS" Is there any wire connected to this Pad? If so which one?

    As above :)

    I still need to order a simple bread board and probes from Amazon to setup a test bed so I'm probably a few days away from finishing the install. I'll keep you posted with my progress. Wish me success.
    Good luck man!!! ;-D

    If I was not clear and you need more info; again, don't hesitate to get in touch!

    All the best, John! And looking forward for my board...............

    p.s: Consider wrapping your RTL SDR in copper or any conductive tape, in order to avoid any signal irradiation inside the radio! I see that you used Kapton tape to isolate it, and be sure to have the conductive tape actually making contact with the ground pad of the board!
     
  4. K3DDT

    K3DDT Ham Member QRZ Page

    New Question: Where does GPIO Pin 29 (White Wire) Now connect to? On the block diagram it shows that it feeds into the OR Gate? LINK.

    I also thought you would like to see some progress.

    Here is my TX9 Tap. I used a single header pin connector with the lead bent down enough just to touch the end of the resistor. This enabled me to have a large enough plastic housing to glue the connector to the board so that I’m not just relying on the small solder connection. LINK

    I decided to glue a small header pin connector to the edge of the PAT. This will allow me an easy way to connect and disconnect the PAT. LINK

    Here is the preliminary mounting configuration. LINK. I do have one problem. The I.FL IPX RF Jumper Cable listed in the Digikey parts list is just a little too short to reach the PAT. I tried turning the SDR either way but it’s about 10mm too short. Maybe change the parts list to include a 150mm cable. I ordered a 300mm cable which should arrive tomorrow so I’m pretty close to a dry run. The other hopefully last and final question is this. You can see my shielded USB cable in the photo. I still have to attach the connector on the end once I know what to do with GPIO 29. However then I’m wondering what to do with the cable shield. Should I connect the shield to the radio chassis ground?

    Thanks again.

    John
    KC3LNW

     
    PY2RAF likes this.
  5. K3DDT

    K3DDT Ham Member QRZ Page

    Ok I just fixed the links to the photos in my previous post. The pictures should be visible now.

    sorry

    kc3lnw
     
    PY2RAF likes this.
  6. PY2RAF

    PY2RAF XML Subscriber QRZ Page

    Hey John!!!!!!

    MAN, your project looks GREAT! I'm super excited and looking forward to it!! Now, to the Qs

    New Question: Where does GPIO Pin 29 (White Wire) Now connect to? On the block diagram it shows that it feeds into the OR Gate? LINK.
    It's the DIS pad.

    I also thought you would like to see some progress.
    You bet!!!!

    Here is my TX9 Tap. I used a single header pin connector with the lead bent down enough just to touch the end of the resistor. This enabled me to have a large enough plastic housing to glue the connector to the board so that I’m not just relying on the small solder connection. LINK
    Man that's a good idea! But I have a story with hot glue.

    I decided to glue a small header pin connector to the edge of the PAT. This will allow me an easy way to connect and disconnect the PAT. LINK
    This was an AWESOME idea! Thanks for the hint, think will do something similar here!

    Here is the preliminary mounting configuration. LINK.
    Heh, things are now taking the final form!

    I do have one problem. The I.FL IPX RF Jumper Cable listed in the Digikey parts list is just a little too short to reach the PAT. I tried turning the SDR either way but it’s about 10mm too short. Maybe change the parts list to include a 150mm cable. I ordered a 300mm cable which should arrive tomorrow so I’m pretty close to a dry run.
    SNAP, I completely forgot about that - That cable was meant to be used to connect the IF port in the Main Unit to the Panadapter - I completely forgot to specify a cable from the PAT to the SDR /o\
    I have just updated the BOM - Thanks for pointing, John!

    The other hopefully last and final question is this. You can see my shielded USB cable in the photo. I still have to attach the connector on the end once I know what to do with GPIO 29. However then I’m wondering what to do with the cable shield. Should I connect the shield to the radio chassis ground?
    When I used the SDR through an external cable, I did not connected the braid to the radio - I just soldered it to properly to the the SDR dongle - and then let the SDR copper tape do the shield/ground reference with the radio.
    Man I would also remove the external kapton from your SDR. Use it internally, on the board (ensuring to leave ground contact) to prevent the copper tape from shorting stuff. The copper wrap would be the good ground connection with your chassis - and the Flat Cables prevents it shorting to some other undesired point.

    Good luck John!!!
     
  7. K3DDT

    K3DDT Ham Member QRZ Page

    PY2RAF, If you are this responsive to online people you don't even know, you must be awesome to deal with in your professional circle. KC3LNW
     
    PY2RAF likes this.
  8. PY2RAF

    PY2RAF XML Subscriber QRZ Page

    Oh cmon man - I'm just giving back, I didn't do this alone - Had a lot of AWESOME people to help me. You as well.

    I was thinking, a small word about GPIO.

    The SDR provides 4 GPIO lines, and you will be only using three of them. The below statements are true if the pads are taken to the HIGH level.

    BYP - The Amplifier bypass, moving the IF signal from IF_IN all way to the SDR_OUT port. A word of caution: This definitely imposes a signal loss/penalty to the radio.
    BPF - Passes the signal through the bandpass filter (still not tested and not verified)
    DIS - Disable. Trips the IF tap

    The values are not critical, just make sure to take note of which GPIO port connects to which Panadapter pad so you can manipulate it - I used Carl Laufer's RTL-SDR rtl_biast tool from https://github.com/rtlsdrblog/rtl_biast/releases/tag/1.0.

    Nonetheless, it is entirely worthy to mention here that the GPIO soldering is 100% optional - The board will work normally without them. Only connect if you want to fiddle with the above options.

    A BIG gotcha here. In the rtl_biast tool, the GPIO ports (actually, Pins) translates as below:

    Code:
    +---------+-----------+
    | SDR PIN | RTL_BIAST |
    +---------+-----------+
    |   29    |     5     |
    |   30    |     4     |
    |   31    |     2     |
    |   32    |     1     |
    +---------+-----------+ 
     
    Last edited: Nov 14, 2019
  9. K3DDT

    K3DDT Ham Member QRZ Page

    I will have to admit that I’m not actually sure yet why and how I need to activate or deactivate the GPIO, but I’ll start researching. What is the default mode of operation is I just leave the GPIO alone?

    Also my cable didn’t arrive today, but I really couldn’t wait any longer and I decided to try and connect everything up for a live trst run. We’ll first some bad luck. I realized I didn’t have a threaded standoff for mounting the PAT. So I figured I would just temporarily remove one of the standoffs used for the SCP. I started to thread it into the hole near the PAT but I dednt realize the threads were different and I broke the stud into the threaded hole. Man I was pissed off. I had to remove the whole main board to get the broken screw out. Then after I put everything back together I used a small piece of 6mm copper tube to make my own board standoff. It worked.

    Then I crossed my fingers and hoped for no smoke.

    We’ll It works.....Here is a short video link.

    Now I still have new questions about OmniRig and HDSDR but I’m going to finish getting my raido back together later this week and try to figure out as much as I can on my own.

    many thanks.

    kC3LNW
     
  10. PY2RAF

    PY2RAF XML Subscriber QRZ Page

    Good morning John! o/

    I will have to admit that I’m not actually sure yet why and how I need to activate or deactivate the GPIO, but I’ll start researching. What is the default mode of operation is I just leave the GPIO alone?
    So. Default mode is:
    No BYP - Signal passes through the RX Amplifier
    No BPF - No band shaping, the entire FI signal is passed forward
    No DIS - The panadapter actually... Working :)

    Take a look at the block diagram, that will be more visible over there.

    Also my cable didn’t arrive today, but I really couldn’t wait any longer and I decided to try and connect everything up for a live trst run.
    <inhales>

    We’ll first some bad luck. I realized I didn’t have a threaded standoff for mounting the PAT. So I figured I would just temporarily remove one of the standoffs used for the SCP. I started to thread it into the hole near the PAT but I dednt realize the threads were different and I broke the stud into the threaded hole. Man I was pissed off. I had to remove the whole main board to get the broken screw out.

    Argh. Yes, it is definitively different screw step/thread. Have to be creative here. I'm also in a sub-optimal scenario.

    Then after I put everything back together I used a small piece of 6mm copper tube to make my own board standoff. It worked.
    Was it good? Do you mind sharing?

    Then I crossed my fingers and hoped for no smoke.
    Magic Smoke....

    We’ll It works.....Here is a short video link.
    HOORRAY!!! You were able to tune some nice tango over there, congratulations! I see that the RX freq is on sync with HDSDR!!! CONGRATULATIONS!!!!!! \o/

    Now I still have new questions about OmniRig and HDSDR but I’m going to finish getting my raido back together later this week and try to figure out as much as I can on my own.
    Glad to hear man - And thanks for sharing your progress!!!

    73 - PY2RAF
     

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