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Setting RF Power to Zero

Mick  W8BE
Mick W8BE Member ✭✭

I do testing for Node-Red with the Flex and when I want to test where I need to xmit I set the rf power to zero so that I don't xmit. I noticed that the pa temp would increase slightly and the other day I was doing this while testing a FT8 flow and where I replied to a cq. I was surprised the the op called me back. Then I realized even with rf power at zero apparently you are still transmitting a signal. So now I always have an antenna or dummy load when I do xmit tests.

Wondering if any has any thoughts on this.



  • KD0RC
    KD0RC Member, Super Elmer Moderator

    Hi Mick, I notice that you posted this in the Legacy Radios category (Flex 5000,1500, etc). Are you seeing this behavior on a legacy radio or on the current 6000 series?

  • Ted  VE3TRQ
    Ted VE3TRQ Member ✭✭✭

    It is entirely possible the low level input (also on the transverter output) was leaking through too your antenna, even though the power amp (100w) was set to no amplification.

  • Mick  W8BE
    Mick W8BE Member ✭✭

    Len, its on a 6600.

    Ted, maybe, but why would I see the PA temp rising...It's not a big deal, I just know now to keep a dummy load or an ant connected...


  • KD0RC
    KD0RC Member, Super Elmer Moderator

    Hi Mick, I will see if I can reproduce the issue on my 6400 so that you will know if this is a one-off problem with your rig or an issue with SmartSDR generally.

  • Craig_KØCF
    Craig_KØCF Member ✭✭✭

    In order to acheive linear amplification, Class A, AB and B amplifiers draw a continuous bias current even when no signal is present. This, obviously, will generate heat in the amplifier.

    73, Craig KØCF

  • KD0RC
    KD0RC Member, Super Elmer Moderator

    HI Mick, on my 6400 running 3.2.39, zero RF means zero RF in all modes. I used WSJT-X in FT8 mode and got zero signal out if the RF Power was set to zero in SmartSDR.

    If you are getting RF out when the slider is at zero, I think you should submit a help desk ticket.

  • Ken Wells
    Ken Wells Community Manager admin

    Hello Mick,

    Is it possible that you are changing the RF output on one band, but that when you change bands the TX Band Settings is changing the power for THAT band? (TX Band Settings table remembers the power output on a band-by-band basis)

    If you want to completely turn RF output off, then you can set the MAX POWER setting to 0 in the "Settings Radio Setup TX" table.

  • John KB4DU
    John KB4DU Member ✭✭✭✭

    I keep a dummy load on ant2 for testing stuff.

  • Mick  W8BE
    Mick W8BE Member ✭✭


    sorry I got so tied up at work I forgot to check the post.. To answer the questions. The power was a zero. I am watching it using Node Red and the radio at the same time. RF = 0, Tune = 0. I have been testing like this for some time. Here is a pic of what the issue is...

    In the pic I am transmitting (vfo freq in red) and power is 0. Yet you can see the temp rise. I would never had thought much about it except when the OP called me back on FT8.

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