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Transmit compressor processing method

Alan Nusso, N4BV
edited June 2020 in SmartSDR for Windows
I would like to know how the transmit audio processing is done in the 6000 series, the compressor etc. Is it done all digitally? Does the audio equalizer work digitally or analog? Thanks, Alan


  • K9DUR
    K9DUR Member ✭✭
    edited January 2017


    All processing is digital.

    73, Ray, K9DUR

  • Ken - NM9P
    Ken - NM9P Member ✭✭
    edited June 2020
    I don't know the exact algorithm, but I do know that it works very well, and doesn't distort the audio.
    On my "Rag Chew" audio setting, with upper and lower cut-offs at 65-3000 Hz, the DX position works really well to add power, but still sounds great.

     When using the "DX+" setting, It is more effective if I raise the lower floor to 200-300 Hz so that the bass frequencies do not make it sound too muddy, and it enhances the highs to maximum punch in a pileup or for weak signals.   

    This is a very nice addition to Smart SDR 1.2.1.
  • W9OY
    W9OY Alpha Team Member ✭✭
    edited June 2020
    It's my understanding the "processor" concept comes from Dave W9GR who discovered how to correct overshoot in the output of a Hilbert transform.   Apparently by not allowing the function to overshoot an additional 2.5 dB in-band power is realized.  Not bad!  There is a QEX article coming out later this year and I will be interested to read the details.  A friend of mine who knows Dave gave me a little low down on this so I know just enough to be dangerous.  

    I think what's most amazing is W9GR contacted the engineers at Flex with this concept and it could just be coded up by Flex and found to be so effective as to be included in our production radios as a simple software upgrade BEFORE it even gets to QEX.  That's like pre-cutting edge functionality, yet thoroughly within the back room engineering tradition of ham radio.     

    73  W9OY
  • Rick Hadley - W0FG
    edited June 2020
    In a similar vein, can someone explain the new Downward Expander and how it can be set most effectively to those of us who seldom venture above the bottom 25khz of the bands.
  • Ken - NM9P
    Ken - NM9P Member ✭✭
    edited December 2016
    Turn your power down to 1, or use a dummy load. Set up your EQ and processor the way you want. Put on headphones. Turn on TX monitor and raise the level to a comfortable level. Key the mike and listen to the background noise in your monitor headphones. Slowly adjust the Downward Expander until the noise and your breathing just disappears. Talk a little to see that it isn't overdoing it. Then you are done! You will be quiet between words and phrases. Go back to full power, and your antenna. Compression and DEXP are independent of power output setting. It works better and is easier to adjust than the one on PowerSDR.
  • Ken - NM9P
    Ken - NM9P Member ✭✭
    edited December 2016
    I can't wait to get my 1500 back from flex repair so I can record my 6500 and run some tests! Everyone else tells me it sounds great, but I want to hear it myself!
  • Al K0VM
    Al K0VM Retired Member ✭✭✭
    edited November 2017
      The purpose of the downward expander is to reduce the effect of back ground noise during pauses in you speech..  The way I adjust mine is fisrt to set you the mic level as you normally expect to operate, then with out speaking, use MOX to key the radio and observe the inband TX noise floor ( room abient back ground noise ) as you adjust the DEXP gain..  I have mine set for a modest (10-20) reduction in the TX noise floor.
      The setting somewhat depends on  the amount of noise your mic picks up..
    AL, K0VM
  • Michael - N5TGL
    Michael - N5TGL Member ✭✭
    edited October 2016
    pre-cutting edge.  I love it!  I do have to comment that the compressor seems to work rather well.  My antenna here isn't the greatest, but I still manage to **** pileups relatively easy.

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