IC-7300 plus linear amp warning

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

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  1. G0GSR

    G0GSR Ham Member QRZ Page

    No, unfortunately not.
    There is "TX delay" but that delays the RF only at start of TX, doesn't affect end of TX.

    I have another radio (Kenwood TS-590) and using the same test set-up, the amp switching behaves impeccably.
  2. WA4SIX

    WA4SIX Ham Member QRZ Page

    Check if lowering your TX delay might lower hangtime?

  3. G0GSR

    G0GSR Ham Member QRZ Page

    Hi Ed.
    No, checked that by setting it to OFF, it doesn't change the "TX tail fault" at all.

    The annoying thing is. The amp relay is opening before the antenna C/O relay which doesn't switch until after the RF output ceases, as it should.

    KD2ACO likes this.
  4. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    I tried a 590 out at a friends house and it was really nice!
    My FT-840 was pretty good about switching, the 857, not so much. The TS-820 is a relay smasher (and why I built the sequencer).

    My new main radio is an ICOM 7610 and it's running with the sequencer so I haven't even looked at this, but now I'm curious. It does have a TX delay function but it may also have bad manners upon release! :eek:

    Will report back. If it's bad too, I'll write to ICOM and see if others have complained. We (Zed ICOM SDR owners) should start something with them as this problem would be super easy to solve with a few additional lines of code.
  5. WA7PRC

    WA7PRC Ham Member QRZ Page

    Have you notified ICOM? o_O
  6. G0GSR

    G0GSR Ham Member QRZ Page

    Apparently the 7610 does not have this rather stupid fault but I will never have one to confirm for myself.

  7. K4MJA

    K4MJA XML Subscriber QRZ Page

    the issue had been reported to Icom in may 2016
  8. G0GSR

    G0GSR Ham Member QRZ Page

    Yes but that was reported to affect full QSK only AFAIK but in fact the same fault affects all modes.
    I am not sure if Icom know this but they are certainly ignoring the reported fault.

    KD2ACO likes this.
  9. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    Hi Frank,

    Here are some quick and dirty photos of how the 7610 behaves. I have an early unit running software v1.03 on the main CPU.


    This is in FM mode at 20% power, no TX delay. There's quite a nasty overshoot before the power settles into where it should be... a long running ICOM feature (but let's not pick on ICOM here... this is a problem with many radios). If a user is running an amp at reduced exciter power, they should have the amp loading set for 1.5x (or full normal, whichever comes first) what the power is dialed to in order to keep from arcing the tank components.


    This is keying up in RTTY with 20ms TX delay. No overshoot... interesting. I checked the overshoot vs. TX delay and found out that it happens in all carrier modes until 20ms after keying. What this means is that in carrier modes at reduced power, you will have power overshoot unless the TX delay is 20ms (ouch, guys)!

    I chalk this up to sloppy software/hardware design. The power limiting is probably happening in the analog domain (with the ALC circuit) and ALC attack time constant doesn't go away during key-up (they need to feed the signal that lets the power limiting clamp the control voltage after the attack delay timing caps for quicker action).

    At least the key release seems well behaved in this radio. This timing stays the same regardless of the TX delay setting.


    Designing gear is harder than it looks to the uninitiated, but I think you're correct about this kind of problem being silly.

    Now that you sparked my interest in this issue, I'm going to run my radio with 20ms of TX delay. Back into the sequencer it goes anyway, the wiring is all in place. :p
    Last edited: May 24, 2019
  10. G0GSR

    G0GSR Ham Member QRZ Page

    Yes, that's much better. Just shows that Icom haven't forgotten about what's required with the switching, the guy who knew must have been out to lunch when they specified the 7300 :)
    Your RF traces seem to have a DC offset?

    Maybe I will look at power overshoots later... Busy building my sequencer.

    KD2ACO likes this.

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