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Is normal this on 40mts without antenna conected?

YV5WZ
YV5WZ Extra as YV PY HC and General as KOMember ✭✭
edited June 2020 in SmartSDR for Windows
I was cleaning and adding more ferrites to my shack  and  wanted to check how many dBm of noise my radio could have without antenna, looking for any source which could affect my reception ....I got surprised cause I found 110 dBm ( around 3S) on 40 mts and 80 mts.....miles away from quiet station  recommended by Howard K6KY.......
I changed dc power supplies looking it as possible cause ..but....no change.....No wall-mart adapters....I changed from PC to Laptop....no change....not halogen lamp nor neon lamp....no plasma or LED TV's close to shack.......any ideas? or this normal....


Greetings...

George YV5WZ / PY3ZZZ

PS: Not 12 V batteries available at home to test  without DC power supplyimage

Answers

  • Jim Jerzycke
    Jim Jerzycke Member
    edited December 2019
    I'm pretty sure that's "normal".

    Not too long ago somebody asked a very similar question, and a Flex person explained why the S-Meter didn't read "zero" with the antenna disconnected.

    73, Jim
  • YV5WZ
    YV5WZ Extra as YV PY HC and General as KO Member ✭✭
    edited December 2016
    Hello Jim

    Wow!  thanks...I was worried about.....and you know....when you talk about with ham amateurs friends (Icom, Yaesu fan) ...they begging to talk about "some problems" and to have to send back the radio to repair.....hahahaha...Thanks Jim

    Greetings from Venezuela

    George, YV5WZ / PY3ZZZ 
  • Lee - N2LEE
    Lee - N2LEE Member ✭✭
    edited December 2019
    George, on the opposite issue. Have you noticed that the S-Meter is also very stingy ?
    I have not connected a signal generator but it seems no matter the strength of the signal the meter never reads over S-10.
  • KY6LA_Howard
    KY6LA_Howard La Jolla, CA. Paris and Sablet FranceMember ✭✭✭
    edited August 2016
    George Your S meter is reading the noise floor on 40m it's about -115 dBm or near S2-S3 The other SMetrlers LIE. They read Zero which is meaningless.
  • Jay Nation
    Jay Nation Member ✭✭
    edited August 2016
    Lee

    I've seen mine read over S-10. Especially, when I'm transmitting with my FLEX5000A, which sits next to it. Stingy isn't really a good characterization, I've connected mine to a signal generator an Elecraft XG-1. It correctly read the S-9 signal. I've got a couple of other signal generators (uncalibrated antenna analyzers) that will drive it past S-20.
        
     SDRgadgets

    73, Jay - NO5J

  • Doug Hall
    Doug Hall Member ✭✭
    edited August 2016
    The Flex adheres to the standard (such as it is) of S9 being a 50 uV signal, with each S-unit representing a 6 dB change. Quite a few other radios use somewhat lower signal levels to correspond to S9, and an S-unit is sometimes much less than 6 dB.

    So compared to other radios the Flex S-meter may appear stingy, or compared to the Flex the other radios may appear overly generous.
    73,
    Doug K4DSP

  • Lee - N2LEE
    Lee - N2LEE Member ✭✭
    edited December 2016
    Doug this is what I suspected but I would be curious if you see the same (unscientific) results.

    Place your mouse over the S-Meter and when your meter reads S-9 what is the dBm reading you get ?

    I assume Flex uses the IARU recommendation of ...
    For the MF / HF bands, an ‘S9’ signal strength is a receiver input power of ‘-73 dBm’. This is a level of ‘50 uV’ at the receiver's antenna input assuming the input impedance of the receiver is 50 ohms. 
    Again this is not the best way to measure this but when I get a S-9 signal I am seeing -86 dBm not -74dBm. Without a calibrated signal generator I can't tell if this 50uV or not.

    Thanks for the info.

    Lee
  • Jay Nation
    Jay Nation Member ✭✭
    edited August 2016
    Lee 
    My XG-1 which only puts out an nonadjustable 73 dBm, 50 uV signal is read as 73 dBm on all 3 of my Flexradio's. Both PowerSDR and SmartSDR show the same readings. Coincidence, or accuracy? PowerSDR is able to report dBm to 2 decimal places, even then it usually reads 73.something.  

     SDRgadgets

    73, Jay - NO5J

  • YV5WZ
    YV5WZ Extra as YV PY HC and General as KO Member ✭✭
    edited December 2016
    As Always my friend Howard....I appreciate your excellent comment....now I feel I'm going in on right path to my quiet noise station, following your advises

    Thanks

    George, YV5WZ / PY3ZZZ 
  • YV5WZ
    YV5WZ Extra as YV PY HC and General as KO Member ✭✭
    edited December 2016
    Hello Lee......I'm agree with you...
  • KY6LA_Howard
    KY6LA_Howard La Jolla, CA. Paris and Sablet FranceMember ✭✭✭
    edited August 2016
    Thanks George..
  • Doug Hall
    Doug Hall Member ✭✭
    edited August 2016
    I just hooked my old HP-8640B (which hasn't been calibrated in years) to my Flex-6300. I set the output of the signal generator to -73 dBm on 7.030 MHz. I am seeing S9 on the S meter, and when I hover the mouse over it I get a reading of -72 dBm. Close enough for the girls I go out with.
    73,
    Doug K4DSP

  • Lee - N2LEE
    Lee - N2LEE Member ✭✭
    edited December 2016
    hehe  Nice.  Doug thanks for taking the time to do this. 

    Lee
  • Jay Nation
    Jay Nation Member ✭✭
    edited August 2016
    Using Flexmeter and a narrow passband filter would avoid having to hover your mouse over the red bar. It reads the level in dBm from the same source the S-meter is using to generate the red bar. It also displays the reading as dBm to 2 decimal places. Selecting the average readings will smooth out the reading enough to see what's going on. The indicated level is the signal level of the strongest signal in the passband. So narrow it up a little. That might make a difference.
       
     SDRgadgets

    73, Jay - NO5J

  • Ken - NM9P
    Ken - NM9P Member ✭✭
    edited June 2020
    Though some may say the Flex S-Meter is stingy, I say that it is ACCURATE in a world of inflated and inaccurate S-Meters. On many rigs, the meter is callibrated with the preamp OFF, but then normally run with the preamp ON, thus every reading is inflated by as much as 20 dB! On the flex, the meter and the panadapter is corrected so that whether the preamp is on or off makes no difference. The meter is always accurate.

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