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Is this a valid method for setting AGC-T?

Total newbie here, I've had my Flex 6400 for less than 2 weeks. I've seen the video and read the instruction for setting AGC-T, but they seem less than precise on getting the best result.

Yesterday, while seeing 50+ people call ZD9W in Tristan da Cunha, I had an idea. I was only hearing him at best in the minus 20's. What if I opened a 2nd slice on the same frequency , make adjustments, and compare the number of decodes and db level?

Slice A was set to AGC-T at 45 which I got from following the instructions. Slice B I took down slowly to about 15. Decodes went up in Slice B about 10 to 12%. ZD9W went from minus 20's to mid minus teens.

Certainly the increased number of decodes seems like this works. But is the increase in db real or just pushing numbers around?

I would appreciate some thoughts here, I can't believe I came up with something new or good, but if it's valid, it's a lot easier than listening for some unknown level of noise!



  • Tim K9WX
    Tim K9WX Member ✭✭✭

    My experience has been that the Flex recommended way of setting AGC results in a too high setting for me. Across the board.

    For FTx modes, in particular, I have had the best luck not listening to noise but adjusting AGC so that my waterfall looks like the waterfall examples in the WSJT-X user guide. Page 28 in the current version of the guide shows this:

    And my waterfall just now on 40 m looks like this:

    Tim K9WX

  • Al_NN4ZZ
    Al_NN4ZZ Member ✭✭✭

    If we eventually get this new feature you will be able to set your preferred AGC-T level. the automated feature will keep it set to your preferred level across bands, conditions, and different antennas and even the noise level changes you can see when rotating a gain antenna. It is the #1 most requested idea by number of votes.


    Regards, Al / NN4ZZ

    al (at) nn4zz (dot) com

    6600 SSDR V3.5.9

    TGXL 1.1.20

    PGXL 3.7.32

    Win10 Pro V2004

  • Erik Carling EI4KF
    Erik Carling EI4KF Member ✭✭✭

    You can already automate the correct setting of AGC-T using SDC. I can testify that it not only provides the optimum setting at the commencement of any session or band change but it also dynamically adjust as conditions change. It works very well on all modes.

  • Tim K9WX
    Tim K9WX Member ✭✭✭

    @EI4KF: What is SDC?

    Tim K9WX

  • Tim K9WX
    Tim K9WX Member ✭✭✭

    @NN4ZZ I would settle for having SmartSDR remember last AGC settings by band and by mode.

    Tim K9WX

  • John KB4DU
    John KB4DU Member ✭✭✭✭

    Well, I have found it works better for me if I start at the low end and work my way up.. that way there is no agc to overcome. Usually around 35-38 works well.

  • rah50
    rah50 Member ✭✭
    A lot of different ways of dealing with AGC-T!

    I certainly would vote that FR adds this to SDR. I downloaded the SDC program, but it looks like I would need to register or pay for the program to get the Smart SDR tab. I'll look into that.

    However, I would still like some comments on whether my methodology is valid please!

    Thanks all.
  • Erik Carling EI4KF
    Erik Carling EI4KF Member ✭✭✭

    You can make a small donation to Yuri UT4LW for SDC, whatever you deem appropriate. Or not of course.

    Quoting so-called optimal threshold figures here is pointless because many factors affect where your radio is actioning AGC only on radio signals and not on noise and will differ for every individual situation.

    The Flex guide (this is for the static setting) is

    • Check the AGC Speed setting for the mode and band conditions. When in doubt, start with MED (medium).
    • Tune the slice receiver to a quiet spot between stations where you are listening so that you are only hearing the noise floor.
    • Starting with the AGC-T at a high value; 50 is a good starting point. Adjust the AGC-T slider slowly to the left to lower threshold values until the background noise level just begins to decrease and then set it a little lower. Make the adjustments slowly and wait a little bit after making a change so the AGC has time to react to the changing threshold levels.
    • Once you find the threshold level where the volume of the band noise starts to decrease, this is the AGC-T "sweet spot" or the "knee" of the AGC algorithm. Depending on band conditions, if the AGC-T is set below 25, you may have to compensate for the loss in audio gain (volume) by increasing the slice or master AF volume to a higher value. For very quiet bands, the AGC-T may be as low as 15 or 20.
    • Tune the slice receiver back to the frequency where there are signals of interest present.

    In real life, the noise environment changes constantly. In many cases, when it rains noise levels drop. Sometimes it is the opposite. A solar storm can increase noise. A manual setting at 9am may be very different to one at 10am. A noise level on one band will be different to another band. There is no one setting fits all. That is why there has been a demand for dynamically or automatic AGC-T contol, for many years actually. Yuri, with one of the many features for Flex users in SDC, provided dynamic control soon after receiving his 6400. As I said, it works exceptionally well. I monitor the AGC level constantly (using Stream Deck)

    This is my current figure on 160m at sunrise. On other bands as the day progresses, the figure varies quite a lot and I have extreme confidence that the receiver is being always optimized.

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