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. K3DDT

    K3DDT XML Subscriber QRZ Page


    I finally got the I.FL IPX RF Jumper and I was able to close up the radio last night but it was too late to play around. After work today has been my first chance to really spend time with the new Radio/SDR PAT Combination. I've got HDSDR configured properly now to control the radio with OmniRig and controlling the RTL-SDR with ExtIO. It's pretty intuitive once you go through all of the menus. Having the ability to monitor 3.2Mhz of radio spectrum substantially increases the usability of the FT-991A. The timing was good too because there is a big Contest going on so there is a lot of activity on the 40m band today, so setting the scope bandwith to 250KHz allowed me to quickly jump around from station to station monitoring a lot of activity.

    I wanted to report some usual anomaly that I've discovered. Initially I was using the speaker on the 991A to monitor audio because I didn't realize how to select the sound card output in HDSDR. Eventually I got that part figured out too however there was a very loud and persistent tone which came in on the SDR that I didn't hear while listening through the 991A. It occurred on ALL bands and in all modes. I noticed that if I adjusted the AGC on the SDR the dB level of the tone would decrease slightly but I could never remove it. Once I tuned to some frequency without much activity I was able to isolate the signal. Check out the image below. You can see the spike about 50dB above the noise floor. The tone is exactly 1475Hz below the tuned frequency.

    It's really strange, isn't it? I'm wondering if you have experienced anything like this on your own setup, or if you could comment on the possible sources of the signal?

    I'll try to compile and install the RTL-SDR rtl_biast tool to see if enabling GPIO BYP or BPF changes the situation and report back.

    By the way I wanted to ask, do you ever monitor any Wires-X rooms? If so I would love to make voice contact one day and personally say thanks. (I'd offer to try and make contact via HF but I don't think my 100 watt output, 40m dipole or my operator skills are at that level yet)

    Audio Spike.JPG
  2. K3DDT

    K3DDT XML Subscriber QRZ Page

    OK I figured it our myself. There is a setting in HDSDC under calibration, called DC Removal Calibration for RX. I just set this to AUTO and it seems to block (Suppress) this signal.
  3. PY2RAF

    PY2RAF XML Subscriber QRZ Page

    @KC3LNW good morning John - Apologies for the delay, I was with family at the country and without access to the radio - and thus, unable to validate the data.

    I'm glad you sorted out that your issue was the DC signal at the center of the tuning frequency.

    John, I was positive that I had documented this at the Wiki and I was about to write a Read the Fancy Wiki reply to you, but guess what: I did not ;-P

    Apologies for that, and how could I overlook that - it was a pain point to me here.

    I have JUST updated the Config wiki (https://github.com/rfrht/FT991A-PAT/wiki/software-configuration) including the DC removal settings. Thanks for bringing this to my attention.

    SINCE WE ARE HERE, I'd also bring to your attention some noteworthy items here.

    In my Panadapter, I have three faint but constant signals - regardless of the band that you are tuned in. Probably something generated inside the radio. See the image below:

    In that test I tuned to different frequencies in different bands (HF, V&U), but the signals are over there steady and still. Not a deal breaker, but a FYI.

    Also, when you are tuning, you may find signal images. They are rooted on nearby strong signals that overloads the SDR front-end and spew images in the spectra. The only way to counteract it is reduce the SDR gain. Notice that the image signal moves in a different direction when tuning.

    P.s.: In the RF Front-end I found the following settings to match better the audio. I have updated the source files but takes a while in Github to reflect:

    And FINALLY, yes! We do have a WIRES-X Repeater here, let's sked it!!!!

    73 - Have a great week!!!!
  4. K3DDT

    K3DDT XML Subscriber QRZ Page


    No need to apologize for anything. Radio time is fun time not work time. I'm actually glad I was able to discover the solution to my problem.

    I too have at least two faint signals at normal gain, but when I turn the gain very high I can see more spikes. These seem to be outside of the mode band and do not appear to cause any audio interference from what I can tell.

    Regarding the inverse signal images I have these as well. I noticed them on the SDR at HF even before modifying the RTL-SDR and installing it into the 991A. I think this is just a limitation of the RTL-SDR hardware. In fact I also have an Airspy HF+ and this device too will pickup ghost signal images at high gain, so I don't see much of an issue other than inconvenience.

    My next task is to see if I can find a way to use Ham Radio Deluxe and my laptop to transmit CW or other digital modes, while still using the Panadapter features. It may not be possible because Omnirig is using the USB ComPort interface that HRD wants to use to activate PTT. If I figure out a solution, I'll be posting it here.

    As for scheduling a Wires-X chat, I usually work from 0600 to 1800 every day then have dinner with my wife late evening. So, my usual opportunities are on Weekend Mornings. The American-Link channel (ID 21080) is very active but also very friendly. I notice that Sao Paulo time is +2 hrs from my time near Washington DC so you could let me know when you usually like to have radio time and I'll try to be available.

    Later 73 KC3LNW, John
    PY2RAF likes this.
  5. PY2RAF

    PY2RAF XML Subscriber QRZ Page

    Well guess what, you've got a great radio:


    I use the DB-9 serial port for the Panadapter, leaving the USB Serial port for other app needing to command the radio!
  6. PY2RAF

    PY2RAF XML Subscriber QRZ Page

    Hey John! o/

    I couldn't find your e-mail in QRZ so I'm resorting to the thread - Drop me a e-mail (good on qrz) and let's sked it!!!


    - RF
  7. K3DDT

    K3DDT XML Subscriber QRZ Page

    We'll I went ahead tried to setup the RS232 along with the USB Serial Ports and I could get them both to work, but I could NOT get HRD to transmit under any circumstances. I'm probably doing something wrong with the radio settings. After a few hours of trying so many different things, I disconnected the RS232 CAT Port and reset all of the settings back to how I had them working previously. Just to make sure I wasn't crazy. Then I started looking closer at the HDSDR Menus. I found a menu called DDE to HDSDR. (See Screen Shot Below) It seemed like HDSDR had some built in functionality to work with HRD.

    I got it connected but still could not have "Three Way" Control between HDSDR, HRD and the FT991.

    Then while doing some more interweb searching I discovered This document describing how to us the SDRPlay & SDRUno with OmniRig with HRD, to control the radio at the same time. Even though the configuration was for SDRPlay and SDRuno the concept seemed to be the exact same solution I was looking for with HDSDR/HRD. It took a while but eventually I found a configuration that worked! With DDE enabled in HRD, I modified the Front End Settings in HDSDR (See Image Below). Now HRD controls the FT991 though the USB port and at the same time has a two-way control link with HDSDR Though the DDE Interface.

    It works GREAT...I cannot be more satisfied with the Panadapter design and how easy it works. What a great enhancement to the FT-991.

    Here is a short video of the setup in action.

    73 K3DDT (Formerly KC3LNW)

    Attached Files:

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  8. PY2RAF

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    HOLLY MOLLY; I'm officially impressed!!! o_O

    Man, that looks NIFTY - There's a seamless integration with HRD and HDSDR - Look AWESOME! \o/

    I'm very glad to see the result that you got over there, John! This is the reason the project was entirely shared - so people could reuse, rethink, remix, reboot - Just like I did too, because others were kind enough to share their work - This is Open Source at its full glory!!

    My congratulations John!!! \o \o \o
  9. PY2RAF

    PY2RAF XML Subscriber QRZ Page

    Hello, QRZers! \o

    New Branch:
    Lite Edition!

    After pondering John's implementation (and other potential people) questions, I concluded that the board contains a lot of extras that while interesting for my use case and experimentation, might be just useless and needless for others. And I could craft a simpler version.
    Sporting a simpler (32 parts vs 48 in the original) and cheaper ($15) BOM, this branch features the basic-only: No fancy GPIO or experimental features; a single RF switch instead of 5 (which is challenging to stay polite to solder): only the panadapter, the main RF switch (inhibits the Panadapter during TX), the amplifier and a sober no-BS board.

    Link: https://github.com/rfrht/FT991A-PAT/tree/PAT-Light


    - RF.
  10. K3DDT

    K3DDT XML Subscriber QRZ Page


    That's quite nice of you to create a scaled down revision O. I think it does indeed make the project less daunting and more accessible to most people. Sorry for not responding sooner, but it's Thanksgiving week in America. Work has been crazy leading into the holiday and then come the family obligations. Not much time to do anything else.

    73 John

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