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Relationship of AGC-T value to dBm

KD0RC
KD0RC Member, Super Elmer Moderator
in SmartSDR for Windows

Is there a conversion (even an approximate one) from the 0 - 100 ACG-T value to dBm for the Flex 6000 series radios? If there was a chart or formula, I would really love to see it.

Thanks & 73,

Len, KD0RC

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Answers

  • KD0RC
    KD0RC Member, Super Elmer Moderator

    @Tim - W4TME

    Hi Tim, does such a conversion exist? I am curious as to where I really have the AGC-T set relative to the noise.

    Thanks,

    Len

  • Patrick
    Patrick Member ✭✭✭
    edited November 2020

    AGC-T is on the decoded side of the signal and relates to audio level dbm which varies greatly from the RF dbm levels as seen on the signal level meter. Applitude modulated or carrier signals and the demodulated signal can and do vary proportionally if AGC-T is wide open. Then when you tighten up on the AGC the audio will now only vary less then the non demodulated RF signal at the antenna terminals. So there really is no constant that can be used to compare audio to RF dbm levels.

  • Eric-KE5DTO
    Eric-KE5DTO Administrator, FlexRadio Employee admin
    edited November 2020

    Technically, the AGC-T (AGC Threshold) control sets the max gain that the AGC system can possibly add, given an input signal that warrants such gain. The units are in dB directly.

    Note that because this is simply setting a gain, no conclusion can be made about the level of a signal from the AGC-T setting alone. Having said that, as the setting is ramped up, the signal is much more likely to approach the target (nominal) audio level as smaller and smaller signals can achieve the target due to the additional allowed gain. This is why it is obnoxious to our ears to have the AGC-T turned all the way up with no signals present as it simply amplifies the noise floor all the way up and why it is important to have the AGC-T adjusted to amplify reasonable signals while not swamping the audio with noise.

    This article covers the subject of AGC and how to set it up pretty well: https://helpdesk.flexradio.com/hc/en-us/articles/360029494371-How-does-the-Automatic-Gain-Control-AGC-work-in-SmartSDR

  • KD0RC
    KD0RC Member, Super Elmer Moderator

    Thanks for the response Eric. Yep, I have seen that article, and am able to set my ACG-T accordingly. What I was hoping for is a correlation of the AGC-T value to the dashed yellow line in the graphic in the article. I am always curious as to how much over the noise I have my AGC-T set.

    73,

    Len

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