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

    Yes about the RF DC offest, it's after a little sampler that is on the exciter line (I unplugged it from the station monitor scope and jammed it into a DSO).
    Quick N Dirty R us... :oops::p
    back to the salt mines here...

    Show us your sequencer when it's going! Fun times...
    Last edited: May 24, 2019
  2. G0GSR

    G0GSR Ham Member QRZ Page

    Hi Chris,
    I can't see any power overshoot on FM or RTTY with the power set to 20W.!!! (TX delay set to 25mS)
    With TX delay set to OFF, there is still a 1mS delay.
    I also confirmed that the TX tail problem is still there and of course, it is not going to go away.

    IC-7300 power set to 20W (FM) start of TX, 20mS/div.​
    But I do think you have a diode in your RF probe :)

    KD2ACO likes this.
  3. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    Yes there are diodes in the sampler for the exciter. I was too lazy to set up a big RF attenuator and instead, just stole the input to the station monitor. Close enough for Rock n Roll...

    That's very interesting about the lack of power overshoot with the 7300! Now if ICOM could put that guy on the same team as the guy who properly designed the release of the 7610, we'd be able to key up and off without arcing tank caps or burning relay contacts! :p

    Actually, take a picture of the key-up with the TX delay off when you get a chance... I'd love to see how that looks.


    Here's that Rock N Roll salt mine I have to work in today. Hot off the press, and it sounds fab!

    Last edited: May 24, 2019
  4. WA4SIX

    WA4SIX Ham Member QRZ Page

    For safety, I run an attenuator on every amp & run the rig at 100W.
    That way, I can use any rig with any amp that I have.
    My newest is an IC-7100 with a 7000 & 706MKII
    THe Swan CX500 does not get to play with amplifiers.

    Now, I am building a LimeSDR-USB with an FT-857 PA chassis. There is a bunch of junk in the middle. I will not even bother going without the attenuator.

    I would rather waste electricity than pop LDMOSs.

    KD2ACO likes this.
  5. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    OK, OK! This weekend, in between the steaks and beer, I'm making a proper attenuator to take better pictures with.
    Your nice screen shots have inspired me. :p

    Chris @KD2ACO

    ~~~~ proudly upholding the "amateur" in amateur radio ~~~~
  6. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    Hi Frank,
    It took about 15 minutes for me to find the parts and put together a (roughly) 10:1 attenuator to feed the scope.
    Ahhhh, much better. I'm going to feed you some pictures in case they are interesting or offer insight. I would think that our radios were designed by the same team but we can see variations in how they respond to keying. I'm looking forward to your post of pictures after you get your sequencer going (morbid curiosity).

    Click on a pic and it gets bigger.

    Starting with non-voice carrier modes: 30%, 60%, 100% power, no TX delay





    This is what it looks like around 15ms when the ALC is trying to figure out who's the boss. What a mess...


    20% power, 10ms TX delay.


    20% power, 20ms TX delay. It really does take 20ms for this transmitter to collect itself in PSK, RTTY, FM.


    100% power, 20ms delay. This delay is where I'm going to run it now in an attempt to keep spurious garbage off the air.

    In voice modes (where I usually am), there is about 40ms of delay and a slow ramp on no matter what.


    SSB, no delay, 70% power (where I normally run).


    AM 50% power, no delay. This give me 130 watts carrier out of the AL-80b.

    At least in the 7610, the tails always seem OK and about 8ms of decay time before the amp keying line is released.

    Yowza... :p
  7. AA4PB

    AA4PB Ham Member QRZ Page

    Are you using any load, other than the scope, on the PTT output? The PTT output is typically a transistor that pulls the line to ground. I'm wondering if with no external pull up resistor (between the PTT line and +12VDC) the internal impedance might be high enough that the RF bypass capacitors (PTT line to ground - inside the radio) might be delaying the PTT OFF condition for 4mS. You might try the test again with a 2400 Ohm (or so) resistor between the PTT line and the radio's 12VDC supply. The resistor would draw about 5 mA during Tx and might pull the PTT to +12 vdc quicker when it switches to Rx condition if there are no pull-ups internal to the radio. Just a thought.
    K0OKS and KD2ACO like this.
  8. G0GSR

    G0GSR Ham Member QRZ Page

    I am assuming that the 7300 and 7610 share the same amp keying circuitry.
    For my tests, I used the volt-free relay contact with 1k pull-up to an external supply.
    The second Icom keying output does indeed use a transistor collector but has an internal pull-up resistor to 13.8v as this is a keying input in addition to being a keying output.

    Much improved traces Chris :)
    That 100% carrier trace is just weird...More scope time tomorrow, been too busy with the sporadic E on 6m.

  9. G0GSR

    G0GSR Ham Member QRZ Page

    I cannot replicate any strange power over/undershoots on any carrier mode with TX delay OFF. Or SSB with constant tone input at various power levels.
    All traces are "textbook" on my 7300.

    SSB 100W tone input, TXdelay=0. Amp on/off keying + RF output.

    With TX delay set to OFF, there is approx 9mS delay between "amp key" and signal ON.

    IC-7300-SSB-50% power.png
    SSB, tone input showing amp "unkeying" 4mS prior to RF output ceasing.

    Amp OFF keying fault is another matter and present in all modes regardless of TX delay, time of the month and moon phase.
    Still no reply from Icom UK tech support.

    WB6BBB and KD2ACO like this.
  10. KD2ACO

    KD2ACO Platinum Subscriber Platinum Subscriber Life Member QRZ Page

    Wow, that’s such an odd problem. I’m searching for a 7300 I can borrow or bring my scope and cables to in order to check if your radio is special somehow...

    What software version is your radio running?

    I wish my “key on” looked like yours! :D
    Last edited: May 27, 2019

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