IC-7300 plus linear amp warning

Discussion in 'Software Defined Radio (SDR)' started by G0GSR, May 21, 2019.

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  1. VK4CAN

    VK4CAN Ham Member QRZ Page

    Okay just recently checked my 7300 and seems I don't have a problem with overshoot but I do have just over 4.3ms of RF after the amplifier send line opens. I also see there is a DC shift on the RF out but that might be just in my DSO I'll look into that. But there doesn't seem to be an acknowledgement of the issue or a fix as yet.

    I haven't used the 7300 on my amplifier a KPA500 yet, currently using my 991A whose timings are correct.

    I't would be easy enough to kludge as mentioned above or use the relay timing from the relay used for PA switching but would prefer a fix from ICOM

    KD2ACO likes this.
  2. G0GSR

    G0GSR Ham Member QRZ Page

    Everybody with a 7300 does ! (and the 9700 has too)
  3. WB6BBB

    WB6BBB Ham Member QRZ Page

    Actually, it may be possible for a technically savvy operator to modify the firmware. Have a look here: binwalk - YouTube binwalk - https://www.youtube.com/results?search_query=binwalk

    Here's a video tutorial:
    Poking around router firmware using Binwalk:

    Look into binwalk, firm-ware-mod-kit, binary analysis tool kit, https://code.google.com/archive/p/firmware-mod-kit/


    Here's a web site to which you can drop the firmware file for analysis: http://www.firmware.re
  4. K1VW

    K1VW Premium Subscriber QRZ Page

    I’ll betcha there have been conversations where marketing and engineering meet and marketing says “we need faster QSK switching to beat the other brands”. Then engineering says “yeah, but you can’t go negative because...”. Guess which side won the conversation? and they are focusing on performance with Icom’s amp, not others.
    Last edited: Aug 6, 2020
  5. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    I bet that someone in software flipped a sign and parked the RF shut off 8ms in the wrong direction.

    Why they won't fix this problem with a firmware upgrade is baffling.
  6. K3LI

    K3LI Premium Subscriber QRZ Page

    Set the delay in your menu. Its in the manual.
    W9FL likes this.
  7. G0GSR

    G0GSR Ham Member QRZ Page

    Richard, I presume that you mean the TX delay setting.
    TX delay, delays the "RF ON" to allow mechanical relays time to operate.
    TX delay and no other menu settings has any influence on this fault which affects the "RF OFF" to "AMP OFF" switching timing.

  8. W9AC

    W9AC Subscriber QRZ Page

    That response shows the problem isn't understood. As Frank has repeatedly stated, the problem occurs on key line "break," after release of the 7300's SEND line. The TX DELAY menu function affects key line "make," to delay the presence of the RF envelope after SEND activation. If Icom haven't addressed the problem by now, they likely never will. They can fix this with one line of code.

    Frank's QRZ page shows a simple but elegant hardware solution to the problem. In effect, he is pulse-stretching the SEND line with a dual CMOS CD4538 precision monostable chip. The CD4538 can be configured to trigger on the leading or falling edge of a pulse. I used them extensively back in the 1980s when I was employed by RKO Radio in Chicago.

    My QRZ page shows a software solution, but it does use my S-QSK Lite hardware. The circuit board Gerber files, Arduino code, and BOM are all available on my QRZ page. The files are free to use for any non-commercial purpose. Where Frank delays the pulse in hardware, I do it with a couple lines of code. Both solutions effectively fix the problem.

    Paul, W9AC
    Last edited: Aug 11, 2020
    KD2ACO likes this.
  9. WA3GIN

    WA3GIN Ham Member QRZ Page

  10. WA3GIN

    WA3GIN Ham Member QRZ Page


    How does the problem manifest? I'm not a CW operator so note sure I would notice...as you said from this recent post not understanding the issue. Point me and I'll go read up. 73 Dave

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