IC-7300 plus linear amp warning

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

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  1. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    Looking through the schematics to see if yours is missing a cap in the keying circuit... there could be a single point where ICOM has a wrong value loaded or yours has a wrong value part loaded. Seeing this trouble out of another 7300 would be interesting. Anyone here have a scope and can take a picture of their 7300's release characteristics?

    4ms is an odd delay. Maybe they are firing the release from the wrong variable in software (i.e. calculating the amp's key release delay from the PTT release instead of the "decay envelope finished" or some such jazz). If it's a hardware fault, shorted diode in a D/R/C setup near the driver transistor's lair...

    Seeing exactly the same timing out of another 7300 with different software would answer a few questions. It seems like we have to answer them ourselves anyway as ICOM doesn't seem too interested in fixing this.

    As for my radio's weird Key On character around 15ms, I didn't even look until reading this post a few days ago because I thought that in 2017, this kind of problem shouldn't happen, especially with a computer running the whole operation. Heck, you can delay the modulation channel a few ms and have the "perfect" compressor in the audio chain like we've been doing in the studio for a couple of decades now.

    Looking at the attack trace on my scope now, I'm pretty sure what's happening is that the power is set with a constant "in the middle somewhere" voltage and then switched to the actual detected voltage around 15-18ms. During that switching time, the value is 'up for grabs' and the output power is indeterminate until switching is complete and the ALC detector and timing have settled in. They did it this way to speed up the Key On timing.

    Since I'm not operating QSK, I'll use a 20ms turn on delay... some of the spikes are truly amazing.
    Last edited: May 27, 2019
  2. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    From what I'm seeing in the very dense 7300 schematics is that all of the timing for bias and relays is performed in software. It looks like ICOM has to update this or you have to make a sequencer.
  3. G0GSR

    G0GSR Ham Member QRZ Page

    Yes, I'm certain it is an error in the firmware and that it affects every single 7300 in the world.
    After-all, I wasn't the first to notice.
    It was apparently reported to Icom back in 2016 but I suspect was only seen as affecting full QSK CW and as the 7300 is terrible at this, I was never going to use it.

    I'm not much of a programmer but can easily imagine either picking the wrong variable or subtracting a value instead of adding could cause this fault.

    But I am not holding my breath and will progress my own solution by modifying the amp keying in an external box.
    Not a sequencer as such, just to delay the amp relay off time.

    Now I am looking at ALC overshoot but need to keep reminding myself "This is an Amateur transceiver, Stop looking so closely"!

  4. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    Stop looking so closely or you'll find more problems! :p

    Another relay arc-life tester from ICOM, ~~~~ "I Can Only Monitor!" ~~~

    Yeah, it takes less time to toss a few components together and just make it go then to send another email into their "auto-circular-file" system.

    I'm glad I looked at mine. I wouldn't have done so until this thread came along. Now I know the 7610 should have the TX delay on to avoid overshoot. :) Zzzzzt

    The 7300's a nice radio anyway and a couple bucks worth of components will calm it down a bit.
    Last edited: May 27, 2019
  5. G0GSR

    G0GSR Ham Member QRZ Page

    Just found this link in another forum:


    Someone else doing timing measurements.

    It looks like Icom has a history of getting the amp switching very wrong but its a lottery as to what older models are afflicted or not.
    Nothing has changed now with the latest batches.

    KD2ACO likes this.
  6. G0GSR

    G0GSR Ham Member QRZ Page

    I have completed my (hopefully temporary) fix for the IC-7300 amp switching problem but would really like Icom to fix this instead.
    But in the meantime....
    I have a box powered from the "Acc" socket containing a bit of simple logic and a beefy FET to switch almost any external amplifier.
    As an added bonus, it removes the contact bounce from the 7300 keying relay and adds a 10mS gap after RF ceases before un-keying the amp.
    The total delay is around 14mS as Icom un-keys about 4mS before RF ceases.

    This is RTTY mode showing the un-keying period.

    This is full QSK CW at 30WPM. A single "dit".

    So I am happy now using this until Icom get this fixed.

    AB6RF and KD2ACO like this.
  7. G0GSR

    G0GSR Ham Member QRZ Page

    So, the test report on the new IC-9700 by Adam, VA7OJ/AB4OJ is published and Icom have been cutting and pasting the same fault to this model too.
    But Adams report is still only mentioning QSK CW as being affected.
    I am pretty sure that the fault will also be present on ALL MODES, like the 7300.

  8. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    I wonder why the management at ICOM hasn’t figured out that this is a problem that is both serious and likely, easily solved.

    I wish we had source code. On staff in my shop is a crack software designer who could probably solve this and other issues in a few days of poking around (kids these days).

    Anyone here have a line on the source code?
  9. WA7ARK

    WA7ARK Ham Member QRZ Page

    Have you figured out how long after the keying signal from the '7300 goes high it takes for the amplifer to do anything about it?

    In my case, my amp has an internal open-frame relay used to switch the antenna. That relay has a snubber diode around its coil for spike suppression... It probably takes 50ms for the armature of that relay to begin to move after the keying transistor inside the '7300 turns off, long after the RF quits dribbling out of the '7300..

    Maybe Icom did me a favor. For me, this is a feature; not a fault....
  10. G0GSR

    G0GSR Ham Member QRZ Page

    Yes, I appreciate that, there is always the possibility that Icom have done this deliberately.
    But I seriously doubt it as they have to cater for amps with PIN switching which switch within a microsecond.
    And of course, the IC-7610 doesn't have the fault even though previous models do.

    I think this just sloppy programming. Other manufacturers also have a habit of carrying serious design faults through a series of newer models so this is nothing new. They don't listen either, just think about the $$$$

    HA3FLT, WB6BBB and KD2ACO like this.

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