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

    Dave. It's only a problem if you are using the 7300 with an external linear amplifier.

    Firstly, in any of the "carrier modes", AM, FM, RTTY, when you release the PTT, the amp is unkeyed prematurely, before the RF output stops. This is the "Fault".
    This subjects your amp RF output changeover relay contacts to a brief full-power arc.

    On SSB, if you use VOX, the PTT will not drop until there is silence, no power output so the the "Fault" will do no damage but if using PTT control, the PTT switch noise will ensure that there is a brief full power click which will also make the amp relay arc.

    CW semi-break-in, no problem but full QSK, very very bad.

    A lot of folk say that this is not causing them problems but they are unaware of the arcing contacts which will, over time erode the relay contacts and promote a failure.
    Of course, if you generate a brief RF arc, for a moment you have a wideband spark transmitter. Something that we are not licensed to use :)

    To switch an RF relay under power is a serious fault. It should NEVER happen.

    I strongly believe that Icom have made a small programming error for the external amp relay and that it could easily be fixed in the firmware and for minimal effort.

    Frank
     
    Last edited: Aug 14, 2020
  2. DL6SEZ

    DL6SEZ Ham Member QRZ Page

    Yes Frank you're so wright!
    I do programming in C#, Microcontrollers in ANSI C and also hard things in Assembler.... and can't understand why they haven't changed it yet since almost 3 years.
    Nearly killed my QSK-5 Ameritron qsk switch with this wrong programmed SEND output behaviour.
    Wondered why the fuse lamps in the qsk switch started flashing with my cw signs.
    Searched the Internet and have to state:
    THANK YOU VERY MUCH TO ALL
    here doing a fine job with your measurements and analysis!
    Couldn't believe what i have seen with the qsk switch and the IC7300.
    Added a NE555 retrigerable Monoflop on the SEND output of the ACC connector of the IC7300 with 10ms delay as others have proposed here and everything is fine now.

    73 de Chris DL6SEZ
     
  3. WB6BBB

    WB6BBB Ham Member QRZ Page

    [QUOTE="G0GSR, post: 5566007, member: 13734"
    A lot of folk say that this is not causing them problems but they are unaware of the arcing contacts which will, over time erode the relay contacts and promote a failure.
    Of course, if you generate a brief RF arc, for a moment you have a wideband spark transmitter. Something that we are not licensed to use :)

    To switch an RF relay under power is a serious fault. It should NEVER happen.

    I strongly believe that Icom have made a small programming error for the external amp relay and that it could easily be fixed in the firmware and for minimal effort.

    Frank[/QUOTE]

    The response I received from Icom below, indicates that there may be a future (presumably firmware) update to address the IC-7300's hot-switching issue:

    ======================================================================
    To: ldighera@att.net
    Subject: IC-7300 Amateur radio transciever [Incident: 201001-000004]
    From: "ICOM America Technical Support"
    <icom@mailca.custhelp.com>
    Date: Fri, 2 Oct 2020 14:58:09 -0700 (PDT)

    Recently you requested personal assistance from our on-line support center. Below is a summary of your request and our response. We will assume your issue has been resolved if we do not hear from you within 3 business days. Thank you for allowing us to be of service to you. To access your question from our support site, click here http://icom.custhelp.com/app/accoun.../AvMt~QpxDv8S~Xv7GuYe~yL3wf8qXi75Mv~T~zj~PP8a

    Subject
    IC-7300 Amateur radio transciever
    Response By Email (Rick) (10/02/2020 02:58 PM) Greetings Larry,

    Thank you for contacting Icom America.

    This was submitted for testing and might be addressed in a future update. Unfortunately, there is no information available at this time about which update will include this. Click here for information regarding Warranty Registration, Service/Repair Authorization form, Knowledge Base & Technical Support: http://www.icomamerica.com/en/support/default.aspx

    Note: Mention of third party products or services is provided for customer convenience and does not imply an endorsement or quality assurance by ICOM America.

    Sincerely,
    Rick
    Technical Support Representative
    Icom America, Inc.
    12421 Willows Road NE
    Kirkland, WA 98034

    _ Auto-Response By (Administrator) (10/01/2020 07:59 AM) The following answers might help you immediately. (Answers open in a separate window.)
    Answer Link: Free Software/Firmware Downloads for All Amateur Radios
    Answer Link: Cloning / Programming Errors
    Answer Link: The amateur radio US Grid Square Map
    Answer Link: Marine Radio Installation and Grounding Resources
    Answer Link: Amateur: Mobile Radio Installation Guide

    Customer By CSS Web (Larry Dighera) (10/01/2020 07:59 AM) When is Icom going to address the hot-switching issue?
    Please see attached image.
    Question Reference # 201001-000004
    Date Created: 10/01/2020 07:59 AM Date Last Updated: 10/02/2020 02:58 PM Status: Waiting for Research
    ======================================================================

    So, it appears that the IC-7300's hot-switching issue was "submitted [to some unstated entity] for testing," presumably as a result of my bringing it to Icom's attention.

    Still no response on this issue from Ray Novak ...

    Best regards,
    Larry
    WB6BBB

    PS: There is a suggested hardware workaround here:

    ======================================================================
    To: <ic-7300@yahoogroups.com>
    Subject: [ic-7300] Amplifier PTT Relay Switching Time Problem
    From: "'Jim W7RY' jimw7ry@gmail.com [ic-7300]" <ic-7300@yahoogroups.com>
    Date: Wed, 20 Dec 2017 06:52:31 -0600

    And while we are discussing problems with the IC7300, there is also a problem with the amplifier PTT relay in the IC7300.

    This relay is what controls your linear amplifier keying line and it is plugged into the “SEND CONTROL JACK” on the rear of the radio.

    The problem is that the relay releases ~2 mS BEFORE the RF stops flowing out of the radio!

    In other words, it makes your linear amplifier HOT SWITCH at high power. It’s especially a big problem with VOX (break in) CW and RTTY. I burned up the input antenna switching relay in my homebrew amplifier because of the issue.

    The fix is to eliminate the internal relay and drive and external (or internal) switching system driven from the T9 line in the radio. T9 is switched 9 volts that the transmitter used for control. T9 goes high (logic 1) at ~4 mS before (controlled by TX DELAY HF, see below) RF flows from the radio. And releases 2mS after RF stops flowing. The pre-key delay is adjustable from the relay menu setting “TX DELAY HF” as depicted on page 8-3 of the manual.

    PTT/amplifier control timing is not critical on release as long as RF STOPS flowing AFTER the relay releases. The delay in your amplifier relay is then purely mechanical. If it takes 10 mS that is fine. If it’s 1mS that is fine too. As long as it does not hot switch.

    Hot switching at the start of your transmission is controlled by the setting of “TX DELAY HF”. So if you have slow relays (large open frame type) you can adjust this time up. 10 mS is the typical delay time for these types of relays in a typical SB-200, SB-220, older Ameritron, Amp Supply etc... Vacuum relay RF switching is about 3-4 mS. If you use a speed up circuit, (like the W7RY QSK Boards) it can be as short as 1.5 to 2.0 mS.

    Hot switching of the RF relays in your amplifier can cause pre-mature relay failure, and arcing in the band switch, tune capacitor and load capacitor. Because the high power output side of the relay can open under full power. Hot switching can also show up as SWR issues on the IC-7300. Because the IC-7300 will be operating without a load for a short time because the T-R relay in the amplifier is open or opening while the IC7-300 is still in transmit mode and producing RF and the amplifier relay is being told to release by the radio during transmit.

    I have oscilloscope shots of the problem that I will write up and post in the Yahoo IC7300 groups file section when I have time after Christmas.

    73
    Merry Christmas
    Jim
    W7RY
    =====================================================================

    =====================================================================
    To: <ic-7300@yahoogroups.com>
    Subject: [ic-7300] Amplifier PTT Relay Switching Time Problem
    From: "'Paul Christensen' pchristensen@ieee.org [ic-7300]" <ic-7300@yahoogroups.com>
    Date: Wed, 20 Dec 2017 08:28:11 -0500

    >”The fix is to eliminate the internal relay and drive and external (or internal) switching system driven from the T9 line in the radio.”

    Jim,

    Several of us have documented the hot-switching issue with our DSOs, going back to the spring of 2016. We’ve asked Icom to pulse-stretch the release of the amp key line in break-in mode. To date, there’s been no interest. However, I am not sure anyone has made a measurement since the release of v1.2 firmware. Anyone?

    In the event the issue is not corrected in v1.2, then I like your idea of using the T9 sample point. Several of us have installed DIP headers in place of the AMP relay (search the Yahoo 7300 archives for a discussion from last year). This mod allows for bringing out the switching transistor’s open collector to the rear panel RCA phono jack. So, those of us who have made the mod enjoy silent amp key line switching. To your point, moving the base sample of the switching transistor to T9 seems like an easy fix, especially if the pre-existing mod has been implemented.

    It's a shame that the customer must make hardware fixes when a couple lines of code will pulse-stretch the amp relay. One line of code does it with my microcontroller-based S-QSK project.

    Paul, W9AC
    Posted by: "Paul Christensen" <pchristensen@ieee.org>
    ======================================================================
     
  4. G0GSR

    G0GSR Ham Member QRZ Page

    Yes, I can confirm that the fault is NOT fixed in v1.3 in which all my tests were carried out.

    I have contacted Icom (UK) twice and had nothing more then an automated reply, nothing else.
    They are not taking it seriously or passing my message onwards.


    So there is hope but I'm not holding my breath...

    Frank
     
  5. K7JOE

    K7JOE Ham Member QRZ Page

    Frank, I'm curious if the 100uF capacitor on pins 2 and 3 of the 13 pin rear accessory port fixes the problem? That would be a simple and quick fix for anyone running an amp with high speed switching? Is this connector parallel to the RCA jack for relay key ? I assume it has no effect on initial key close time and only delays the key open time of the fast switching amplifier until the RF tail of the radio totally dissipates? I use an ameritron ALS600 with the AD5X upgraded relay board and DIP relays which are very fast, fast enough to run QSK CW at 35 WPM no sweat.... I also see the issue across all of my IC-7300 units. (The IC7610 does not have this issue, thanks goodness). I can see very distinctly in carrier modes (AM, FM, RTTY) and when audio is applied during unkey on SSB. A sequencer is a nice option, but a 10 cent capacitor solderled to a $3 13-pin DIN plug at the back of the radio is an even cheaper and almost fail-safe fix. Can you go back to the original post #2 in the thread and update us pls on that as a "fix"? Or did you ever build that sequencer ? I see them available for 25 bucks or so.... just curious. Another much needed IC-7300 after-market device. thank you.
     
  6. G0GSR

    G0GSR Ham Member QRZ Page

    Yes, it does work and I'm surprised that no-one has apparently tried it or even commented on it.

    I did build a simple sequencer as adding the capacitor has an unfortunate side-effect. I have a "tune" switch connected to the external ATU socket and when I release this, the radio goes back to TX momentarily due to the capacitor charging.

    Frank
     
  7. K7JOE

    K7JOE Ham Member QRZ Page

    OK... I'll give it a try and report the results back.
     
  8. WD4ELG

    WD4ELG Ham Member QRZ Page

  9. KE3HJ

    KE3HJ Ham Member QRZ Page

    This certainly looks like it would handle the problem, but I wonder if someone who has a scope and could take and post an image of the results like at the beginning of this thread could try the capacitor on the 13-pin DIN plug, as a few bucks far better suits most budgets than $250. Just a request. Thanks.
     
    K7JOE likes this.
  10. K7JOE

    K7JOE Ham Member QRZ Page

    Exactly. A $5 solution .suits me fine... recalling that the russians used a pencil...
     

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