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New to me Flex1500 and Confusion over RF Output

Hi All

I know its an old radio, but this week I picked up a secondhand 1500 to have a play with SDR during these dark winter lockdown evenings. It seems to work well, I have KE9NS PowerSDR setup on my 5th gen MS Surface Pro (i7, 16GB RAM). I have literally spent hours trying to set it up to optimise use for SSB phone and I am making limited progress. The main issue I have is pretty low RF output according to my meter its putting out a max of 3.8 watts even after following many tutorials on the web to configure the settings (with drive set to 100). I have set the tune drive to max as well and tested, again it struggles to reach 4 watts.

Am I missing something here can someone offer any advice on what I can try next or does it sound like a fault on the radio?


  • Ken - VE5KC
    Ken - VE5KC Member ✭✭

    Hello Paul,

    The meter on the Flex 1500 does not show true out put power. It is only a relative indication of output.

    You would have to use a watt meter to test what the power output actually is.

    This through me off for a while when I first got my Flex 1500.

    This was the answer on another thread:

    Tim - W4TME Administrator, FlexRadio Employee admin

    February 2018

    The FLEX-1500 does not have an SWR bridge, so it cannot measure reflected power or forward power output directly.  The software estimates these values based on a number of different factors.

    SWR is only shown when in TUNE mode.


    73.. Ken - VE5KC

  • 2E0PJY
    2E0PJY Member ✭✭
    Hi Ken,Thanks for taking the time to respond I appreciate your comments. Its a learning curve using this radio, I have to admit but I am getting there. I spent a fair bit of time last night and managed to set the speech setting so I seemed to be getting much better RF out with little ALC so I guess its just a matter of tweaking and testing. I am little surprised the radio doesn't have a SWR bridge of any type built in and I havent read anything about any SWR protection so I wonder how robust the final and PA is for a mis tuned antenna. That said I keep on eye on my main EFHW with a VNA and the swr across the bands I operate is at about 1.8 max so hoping that will be ok..

    73 Paul, 2E0PJY
  • Ken - VE5KC
    Ken - VE5KC Member ✭✭

    Hi Paul,

    I remember that question being asked in the past and the response was that the Flex 1500 finals are fairly robust. You shouldn't have to worry. I use antennas with tuners and during the tuning process the SWR can be very high. I have had no problems with my 1500.

    I suggest you try the search function of this group. There are many years of discussions saved here including lots on the older radios like the 1500.

    Try different wording to find the results for your questions.

    73.. Ken - VE5KC



  • 2E0PJY
    2E0PJY Member ✭✭
    Thank you!
  • g7rfo
    g7rfo Member
    I'm having the same problem with a 3000 Digi gets full 100w tuning gets 100w but audio after setting below 0db alc comp is at 30/40/50w via a atu pwr meter!! very frustrating!
  • WX7Y
    WX7Y Member ✭✭✭

    If your NOT using a calibrated PEP type watt Meter you will not have anything even close to the TUNE power out because your meter circuit doesn't have the ability to read the peak's of your voice because a voice has so many different audio frequencies and artifacts.

    your radio is probably putting out full power you just can't read it using SSB voice if I remember right your output is up to 20 times more then your seeing on a regular WATT meter which with your watt readings are where they are supposed to be.

    Here is a good reference using calibrated PEP Watt meter and a standard calibrated watt meter.

  • 2E0PJY
    2E0PJY Member ✭✭
    Thats super helpful thanks Bret!

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