FT991A and amplifier ALC issue

Discussion in 'General Technical Questions and Answers' started by KU3X, Apr 22, 2019.

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  1. KU3X

    KU3X Ham Member QRZ Page

    ALC from a KPA500 with the FT991A issue.

    The jack on the radio is shared with the FH-2 remote pad and the ALC from an RF amp. You can’t use both functions, you have to pick one. There are no menu functions so you can choose what the jack on the radio is used for.

    Problem: The FH-2 remote pad works just fine. I hooked up the Elecraft KPA500 and ran a cable from the DIN plug on the radio to key the amp. Works fine. Decided to run the ALC from the amp to the jack on the back of the radio to cut the power back on the radio to 30 watts. Unplugged the remote pad and plugged in the ALC line from the amp, the radio did not work. Unplugged the ALC line and the radio worked. On the cable, I used a stereo jack and only hooked up the ALC to the tip and shield to ground. No wire was attached to the ring terminal.

    So the question is, “why does this not work? What did I miss?”

    The manual shows the ring is TX REQ. So what is, ‘TX Req?” I did not hook any wire up to it.

    I called Yaesu tech support, that was a useless call. The guy said cut the ground wire.

  2. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    I don't know, but hope you don't cut the red wire.
  3. K6BRN

    K6BRN XML Subscriber QRZ Page

    This problem sounds familiar...

    Did you set Menu Item 143 to "Lamp"?

    Regardless of what the manual says, I think this switches the REM/ALC jack function from an input (REM) to an output (ALC).

    Give it a try and let me know how it works. I use my FT-991 with a KPA-500 all the time, including ALC. But the KPA-500 (and KAT-500) is 2500 miles away in QTH#2 at the moment.

    Brian - K6BRN
  4. KU3X

    KU3X Ham Member QRZ Page

    Thanks for your response. I will try that today and let you know the results.

  5. KU3X

    KU3X Ham Member QRZ Page

    Good suggestion. When I did that, the radio was able to detect the ALC voltage coming back from the amp. But now, "yet another issue." I'm guessing that the radio just does not work with the KPA500? I adjusted the threshold on the amp and played with the values to see what effect it had. No matter what I did, the output kept dancing around. It was extremely unstable. The output kept changing from no power out to 500 watts out. It was like a bouncing ball as I sent CW. I unplugged the ALC and all went well with 30 watts out of the radio to the amp. Once I plugged in the ALC line, the bouncing ball effect came back into play no matter where I set the threshold level on the amp.

    When I set the ALC on my SB-1000 to work with the TS590SG, it was a super simple adjustment. Like I did with the KPA500, I turned the ALC on the SB 1000 to full on. Keyed the radio in the full power mode and turned the ALC on the amp until I saw my required output from the amp. Once and done. It took only 30 seconds max. I said this only to clarify that I actually know what I'm doing. I think? Hi Hi

    So for me the answer is, which is what I've been doing all along, set up the CS key to take me directly to the power output menu and turn down the power level to 30 watts. Not a big deal to do, but at time I forget to turn it back up to 100 watts. I can live with this.

  6. K6BRN

    K6BRN XML Subscriber QRZ Page

    Hi Barry:

    As I said above, the FT991 and 991A work very well with the KPA-500. I have and use them together at my 2nd QTH. That said, I do NOT use the KPA-500 ALC to "auto-throttle" FT-991 drive back from 100 watts to 30 watts during routine operation - I use it as a "safety" to prevent overdrive and set it to the maximum drive allowed by the KPA-500 (about 40 watts, I think?)

    When I have hit the ALC threshold, drive limiting has been pretty stable. But then I did not have the drive set at 100 watts and rely on the ALC to throttle it back to 30 watts automatically. That's NOT what ALC is really intended to do. Not sure you should EVER routinely rely on ALC action to throttle drive by 70% as this could result in severe output clipping and splatter generation.

    You may wish to call or email Elecraft directly - they are very responsive. Describe what you are doing, what you'd like to have happen and then ask their advice.

    Best Regards,

    Brian - K6BRN
    KU3X likes this.

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