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S meter reads s2 with no antenna connected. Also with no antenna connected the panadapter is -128 dB

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David Decoons, wo2x
David Decoons, wo2x Member, Super Elmer Moderator
edited June 2020 in SmartSDR for Windows
Hi All, On all bands the S meter reads S2 with no antenna connected. If I click on the S meter bar graph it shows -109 dBm. Also the panadapter noise floor on all bands is approximately -128 dBm. I checked calibration of panadapter display to be within 1 dB using an Aeroflex 3920. Dave wo2x

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  • David Decoons, wo2x
    David Decoons, wo2x Member, Super Elmer Moderator
    edited June 2020
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    This is using version 1.0.24 beta
  • Dave - WB5NHL
    Dave - WB5NHL Member ✭✭
    edited December 2014
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    Here is a discussion of s-meter readings. http://community.flexradio.com/flexradio/topics/why_does_my_s_meter_read_s5_all_the_time
  • David Decoons, wo2x
    David Decoons, wo2x Member, Super Elmer Moderator
    edited June 2020
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    I understand the discussion, but with the antenna disconnected the radio should read zero, not S2. It reads -109 dBm with antenna disconnected. No power being applied to receiver. All my other radios do NOT show an s meter reading with antenna disconnected.
  • George KF2T
    George KF2T Member ✭✭✭
    edited February 2019
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    With a dummy load at the SO239, I read -110 dbm and between an S2 and S3.
  • David Decoons, wo2x
    David Decoons, wo2x Member, Super Elmer Moderator
    edited June 2020
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    OK, did some more testing against my TS-990 and here's what I found. The width of panadapter display has effect on total panadapter noise floor (I agree with this. Having panadapter set to show 7.144 to 7.184 has noise floor with dummy load connected @ -142 dBm. S meter is just under S1. Increasing the panadapter width raises noise floor and raises S meter (again with dummy load connected to ANT 1 port). On the TS-990 changing the panadapter width does change panadapter noise floow but does NOT change S meter level. I feel the S meter reading should be a reflection of power within the slice rx passband only and not power within whole panadapter window. Make sense? Dave wo2x
  • Dave - WB5NHL
    Dave - WB5NHL Member ✭✭
    edited December 2014
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    Here is Steve's answer regarding the sampling and bin size related to the noise floor and s meter. The TS-990 isn't a direct sampling radio. http://community.flexradio.com/flexradio/topics/noise_floor_chang
  • Stan VA7NF
    Stan VA7NF Member ✭✭✭
    edited February 2017
    Options
    While we are explaining things - Try tuning in a medium weak station on the AM broadcast band. Now go to ANT and adjust the pre-amp settings. At -10 there is noticeable noise on the AM station which drops some at 0db, drops more at +10db and +20, and comes back slightly at +30db. The actual S/N ratio doesn't change but the (6700) raises the panadapter floor and introduces noise that isn't there. Repeating this for a weak station and it disappears at the -10db setting. This tells me the best S/N ratio is running at +10 or +20db. But at +20 I start to see mixing products (between two BC stations) above and below the BC band.

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