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RF Gain AGC-T 50MHz FT8


Hi, trying to keep learning:

I have a questions regarding adjusting RF Gain / AGC-T for trying to optimize receiving. I'm trying to optimize it for 50MHz FT8 using JTDX (who has a ACGc).

I read the less the better and I used to run WNB and NB both at the same time at maximum and did not had a particular AGC-T level that I did set (was about 70) but in Fast.

  1. Does the RF Gain and AGC-T has to be perform or set on CW 500 mode without any "noise reduction assistance" or can be done on DIGIU 3.0K ?
  2. If I understand correctly once set the "optimum" RF Gain, do we leave it there in order to then proceed with the AGC-T adjustment ?
  3. As mentioned above I used JTDX v2.2.159 and this one has the AGCc option, so not sure if this will impact or interfere with the SmartSDR ACG-T ?
  4. For 50MHz FT8 is usually to have to top RF Gain and Fast ACG ?

Any comments and tips are more than welcome, thank you.


  • KD0RC
    KD0RC Member, Super Elmer Moderator

    Hi Juan,

    1. Set the RF gain as per the manual. Watch the noise level at the right hand side and note about where it is (e.g. -120 dBm). Now change the antenna to an unused port (RX A, Xvt A, etc). Look at the noise level and adjust the RF Gain until it is 8 - 10 dB lower than the level with the antenna connected. You can do this using the mode that you will be operating (like DIGU). This setting will give you the best dynamic range.

    Once the RF Gain is set, set the AGC-T by listening to the noise. Decrease the AGC-T until you just get a reduction in noise. This way, you get optimal AGC action without amplifying the noise unnecessarily.

    2. Yes.

    3. Not sure about this one.

    4. I don't know, but I doubt that it matters much in FT-8 what AGC setting you use.

  • David Decoons, wo2x
    David Decoons, wo2x Member, Super Elmer Moderator

    Also WNB at maximum will cause distortion on receive. WNB is only needed if you have power line type noise. Watch the panadapter noise floor and engage WNB at level of 93. If noise floor drops then it is working against power line noise, if no change then leave WNB off.

    I find I do not use NB as I do not have noise it is effective against.

    as Len pointed out, adjust AGC-T for reduction of band noise but still hear weak signals. 6 meters is usually quiet for me so adding preamp works.

    On 20 meters during the day with WNB and NB off, AGC-T at 44 and preamp off I get almost 60 decodes in a 15 second period (when band open).. Your particular environment and antenna may require different settings but as I said, NB and WNB add RX distortion. I only use WNB at level of 93 with preamp off or +8 dB when I have power line arcing.

    73 Dave wo2x

  • Erik Carling EI4KF
    Erik Carling EI4KF Member ✭✭✭
    edited June 2022

    With JTDX, maximum decodes come from AGC set to Fast on the radio and AGCc set to on in JTDX. With these settings 80+ decodes per FT8 period on a full 20m band is usual (note: this is with maximum decode settings in JTDX).

    I have a .wav file that can be loaded into the software at https://www.dropbox.com/s/uaz0lpich94yqb4/210615_071015.wav?dl=0 which contains 96 decodes between 70hz and 3200hz. Set your waterfall correctly if you want to test it. The caveat with it is that this only helps tune JTDX, you must for on-air FT8 also set the radio correctly as described by Len and David.

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

    The other thing to watch for is see if you are able to decode very weak signals beside very loud signals.

    If you are seeing a -17db signal, and decoding it 100hz from a +20db signal, then things are good.

    Most superhet radios can't do this. Your Flex will and that makes it an amazing radio for these digital modes.

  • Juan TG9AJR
    Juan TG9AJR Member ✭✭

    Thank You (Len, Dave, Erik, Mike) I'm still amaze how incredible the FlexRadio are and how much I keep learning trying to optimize the radio and my use of it.

    Yes Mike my idea in particular on the Magic Band were every dB of less noise and pulling those weak signals out counts, so I'm trying to get those strong but in particular those weak signals.

    73 from the land of the eternal spring, Guatemala !

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

    Hi Juan

    The frustrating part is those with sub par receivers won't be able to decode you. :) I see that all the time.


  • Juan TG9AJR
    Juan TG9AJR Member ✭✭

    Hi Mike unfortunately I do agree as well, thanks for all.