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Low TX output only on 15 and 17?

My 6600 suddenly decided to take it easy when operating on 15m and 17m.

Operating on FT8, with the RF Power slider at 100, RF output is usually between 80 and 100W. Except on 15m and 17m, where the output only gets to 40, maybe 45W.

Moving the slider changes the output proportionally, but it's just that on those two bands, it's half of what you'd expect.

TX Band Settings have all bands with the same 100/10. I tried power cycling and resetting (white power led). No change.

Is there a particular hardware component that might be damaged? Is there a deeper reset/wipe procedure that can be tried?


  • Mike-VA3MW
    Mike-VA3MW Administrator, FlexRadio Employee, Community Manager, Super Elmer, Moderator admin

    Do the following tests:

    • Turn your TUNE power to 100%. What wattage do you get?
    • What is the Audio Level Meter show when you are on 17m and 15m? It should almost be full scale. It is the audio level that drives the RF out power level.
    • measure the DC voltage at the back of the radio while in TX. It should be 13.0V or higher
    • What power do you get when you test into a dummy load. This is a must have device for HF operation and they aren't very expensive or you can easily build your own.

    Before resetting everything, it is better that you take a bit of time and understand the root cause of the problem.

  • sdelmont
    sdelmont Member ✭✭

    Using the [TUNE] button on the flex, with tuning set for 100W, meter shows just under 40W. Results are the same on a dummy load.

    Using the [TUNE] button on JTDX, audio levels are maxed out just before turning red. About -5dB with the peak marker just before 0. meter still shows about the same 40W output.

    Voltage is steady at 13V, not dropping on TX.

    All the output measurements come from the flex via SmartSDR, I don't have an external HF power meter.

    On all other bands, all other variables being the same, output is "normal" at between 80-90W or so. Only 15 and 17 meters show this.

  • WX7Y
    WX7Y Member ✭✭✭
    edited November 22

    Sdelmont, Low Voltage is the most common reason for output power to drop off, The Voltage should be a minimum of 13.8V at the back of the radio to do these test not 13V.

    Where are you measuring the voltage? I would be VERY curious for the Voltage to NOT drop when you go to Tune mode with the Tune PWR slider at 100% and I'll bet you aren't measuring it at the back of the Radio at the PowerPole connectors.

    SIMPLE TEST: You can measure the voltage inside the Radio using FRStack or a small program from K9DUR @ https://k9dur.us/downloads/SDRMonitor/SDRMonitorSetup.exe and comparing what is at the Power Supply.

    Measuring it inside the Radio with the software above is the best place to Start to measure it because you can check the voltage at the Fuse inside the radio with out pulling the cover and work your way out with the Voltmeter Test IF there is more than 1.80V differences between RX and TX.

    Last resort is to do a trouble ticket

  • David Decoons, wo2x
    David Decoons, wo2x Member, Super Elmer Moderator
    edited November 23

    @sdelmont I have converted this to a Help Desk ticket. Please check your email for further instructions.

    73 Dave Decoons wo2x

    Presale Technical Support

  • sdelmont
    sdelmont Member ✭✭

    Using FRStack: V+ was showing 14V on rx and 13.2 on tx. I bumped the voltage a bit to put it on 13.8 during tx, but the problem is still there, 34.4W on transmit, SWR of 1.2.

  • sdelmont
    sdelmont Member ✭✭

    @David Decoons, wo2x I haven't received any new mail from flexradio. I do have a support account under [email protected] (instead of [email protected])

  • Mike-VA3MW
    Mike-VA3MW Administrator, FlexRadio Employee, Community Manager, Super Elmer, Moderator admin

    We emailed you at your [email protected] account today at 9:12 ET.

    You may want to check your spam folder.

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