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Thread: Noise when putting antenna higher

  1. #1

    Default Noise when putting antenna higher

    Hi Guys,

    a few weeks back I posted an item about my reception ... what it boils down to: My antenna is below my rooftop, when putting it higher up above the roof top (to get 360 horizon) my reception goes down.

    Below a picture of the waterfall (top is where the antenna is above the rooftop, bottom is when it is below rooftop)

    compare.png


    My guess: as soon as it gets above the rooftop, it is exposed to electronic noise from solar panels on the roof.

    Any of you experience with this? And is the waterfall consistent with that assumption? (I am really new to this .. so my questions might be a bit naive

    anyway- thanks for your help again!

    Bruno

    (BTW in case it matters: antenna is a home made v-dipole .. tuned (or at least hoping it is tuned) for NOAA satellite reception)

  2. #2
    travis.farmer's Avatar
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    do you have a handheld that can tune to the same frequency? you could use it to "sniff" around for the interference.

    ~Travis
    PASSED Tech exam on 09-09-2017 (awaiting callsign)
    Equipment:
    Kenwood TS-430s, Bucket-base 20 foot vertical antenna
    Kenwood TH-K20a, stock antenna

  3. #3

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    No, I am afraid not... all I have is a SDR dongle

  4. #4

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    The thing I suggest you do is find a continuous data transmission - there are usually loads that warble on and on continuously, and when you find one log the signal strength - then raise the antenna and see what happens. Does it go up slightly, or maybe it goes up but the signal to noise gets worse from your mysterious noise source. It could be wide band noise that has a distinct cut-off - unlikely, or it could be something that makes your SDR appear to have something there. Mine has distinct noise floor changes as I go through the range, and one of them does depend on the antenna - disconnect the antenna and it vanishes! This suggests the thing may be hearing itself, and the image is the result of what comes down the cable mixing with a local birdie - If you do the test with a real continuous signal, and can see it going up and down, then the noise might not really be there.

  5. #5

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    Quote Originally Posted by paulears View Post
    The thing I suggest you do is find a continuous data transmission - there are usually loads that warble on and on continuously, and when you find one log the signal strength - then raise the antenna and see what happens. Does it go up slightly, or maybe it goes up but the signal to noise gets worse from your mysterious noise source. It could be wide band noise that has a distinct cut-off - unlikely, or it could be something that makes your SDR appear to have something there. Mine has distinct noise floor changes as I go through the range, and one of them does depend on the antenna - disconnect the antenna and it vanishes! This suggests the thing may be hearing itself, and the image is the result of what comes down the cable mixing with a local birdie - If you do the test with a real continuous signal, and can see it going up and down, then the noise might not really be there.
    Hi paulears - tnx for your reply. Trying to digest what you wrote I do get some HF AC in the dongle itself might mistakenly be seen as an external radio signal. But could that be impacted by raising the antenna? (I noticed that when tuning the software to a frequency x, I often get two spikes symmetrical around the centre frequency (x-d , and x+d) .. I am pretty sure those are cause by the dongle itself.)

    apologies for the noob questions.. but that is because i am a noob in this field

  6. #6
    M0WAO's Avatar
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    solar panels don't make noise but some Inverters do... mostly the switched mode versions
    73 de Biton - m0wao - echolink 633710
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  7. #7

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    What I mean is that the SDR dongles appear to not only receive via the antenna input, they're also receiving through the case! stray signals seem to be able to get in and cause what appear to be an increase in background noise, but signals come through exactly the same amount of hiss. It's as if there is some odd mixing going on inside the device that produces what LOOKS to be an increase in noise - but listening to the signal, the ratio between the wanted signal and the noise doesn't change? If you find a local-is constant signal, and see how string it is - then raise the antenna so your noise appears, does the signal of the wanted signal go up too? If it does, then the s/n hasn't changed. If the signal gets swamped with extra noise, then that background is real. The issue may be that you can see the noise, but it could be just the display reacting to the wrong thing?

    If when you raise the antenna the noise intrudes and makes reception worse - it's real. If it doesn't, it's not real noise, just poor display design.

  8. #8

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    Quote Originally Posted by M0WAO View Post
    solar panels don't make noise but some Inverters do... mostly the switched mode versions
    that makes sense.. i suppose solar panels produce DC so they shouldn't produce noise... So it might be the inverter(s) ...
    To narrow this down I should ask my neighbour to remove the panels ... no..let's not go there

  9. #9

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    Quote Originally Posted by paulears View Post
    What I mean is that the SDR dongles appear to not only receive via the antenna input, they're also receiving through the case! stray signals seem to be able to get in and cause what appear to be an increase in background noise, but signals come through exactly the same amount of hiss. It's as if there is some odd mixing going on inside the device that produces what LOOKS to be an increase in noise - but listening to the signal, the ratio between the wanted signal and the noise doesn't change? If you find a local-is constant signal, and see how string it is - then raise the antenna so your noise appears, does the signal of the wanted signal go up too? If it does, then the s/n hasn't changed. If the signal gets swamped with extra noise, then that background is real. The issue may be that you can see the noise, but it could be just the display reacting to the wrong thing?

    If when you raise the antenna the noise intrudes and makes reception worse - it's real. If it doesn't, it's not real noise, just poor display design.
    Ok, got you now. if the SNR stays the same, there is no real source of noise. If the SNR goes down, there is an actual noise source picked up by the antenna.

    When I can find some spare time I am going to test this.

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