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Ham Radio - Do antenna tuners help with shortwave listening?

Discussion in 'Amateur Radio News' started by KB7TBT, Dec 20, 2021.

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  1. KB7TBT

    KB7TBT XML Subscriber QRZ Page

    Ham Radio - Do antenna tuners help with shortwave listening?
     
    VE2GCE, VE7JAI, KD9FEK and 12 others like this.
  2. WM6P

    WM6P Ham Member QRZ Page

    With the tuner in it increased signal strength. Did it not also raise the noise level? I am less concerned about signal strength, but striving to signal to noise ratio. Did that improve or stay the same?
     
    N2OTG and (deleted member) like this.
  3. VA3RTG

    VA3RTG Ham Member QRZ Page


    I'm no expert, but I would think that both noise and signal would be changed equally. I'd think that a tuner would be helpful to increase the signal over the noise level in the receiver if needed, but again, I'm not an expert.
     
    W4BUS likes this.
  4. W1YW

    W1YW Ham Member QRZ Page

    If the mismatch loss is roughly 20 dB or more (a very high SWR), the RX noise is often stronger than the input from the antenna, and in that case a better match is dictated. Otherwise, for SWR's less than, for example, 10:1 or less, there is no difference. VA3RTG is correct that it is the SINR that is key.

    The SINR from the antenna remains the same and a tuner does not change, in any way, the power pattern of the antenna.
     
    KC7ZXY, KA4VNM and W4BUS like this.
  5. W9CQG

    W9CQG Premium Subscriber QRZ Page

    Happy Holidays to you too Kevin. From a Fort Wayne expat in Canada, VA3CQG
     
    VA7LTX and N8WI like this.
  6. K1LKP

    K1LKP Platinum Subscriber Platinum Subscriber QRZ Page

  7. KZ4TN

    KZ4TN XML Subscriber QRZ Page

    I always use an antenna turner when SWLing. While the background noise will increase with the signal level, I use the RF gain to cutback on the background noise and, depending on which radio I am listening on, use a DSP filter to improve the clarity of the audio.
     
    N9SA, KC7ZXY, KG4HRU and 4 others like this.
  8. W1YW

    W1YW Ham Member QRZ Page

    Unfortunately this video is factually incorrect. Improving the match does not improve a receiver's ability to detect SWL transmissions--unless the SWR is very, very high (see my response above).

    Modern HF receivers are relatively noiseless, but if the SWR is very high, the input from the antenna is of order or less than the noise of the receive itself. THEN an improved match gives improved detectability.

    A more TYPICAL example--If the SWR is, say, 5:1 or 10:1 --again, for example-- it is the signal to noise ratio of the TRANSMISSION to tthe SKY NOISE or INTERFERENCE 'NOISE" that determines detectability of the transmission. So a conjugate match with an antenna tuner doesn't change that at all, for practical purposes.

    In noise theory, this is discussed as the 'noise figures' of the antenna and the RX ,detectability is defined by bandwidth and 'integration' time.

    Nice discussion in the video about how a tuner works, but this key point on receiving is unfortunately incorrect, save for huge amounts of mismatch from a very high SWR..

    73
    Chip W1YW
     
    K0WWX, AA4MB, WA8FOZ and 6 others like this.
  9. KDBC

    KDBC QRZ Member

    I found the video misleading. He implied with words the SWR match was horrible because the impedance was not 50-ohms. However, if you observed and know what the numbers mean the impedance ranged from 25 to 250 Ohms.
     
    PU2OZT likes this.
  10. W1YW

    W1YW Ham Member QRZ Page

    Here's a simple thought experiment you can do that proves the above.

    First, just as a rough guide, here is a table of some VSWR values,, and the mismatch loss (in dB):


    SWR (approx)mismatch loss (dB)
    18:1 ... 7
    9:1 ... 4.5
    6:1 ... 3
    3:1 ... 1.25

    Put a variable attenuator betwe3n the antenna and the RX port.

    Set the attenuation to infinity (or very high)

    Listen to the receiver. That noise you here is only from the receiver, and thus whatever goes INTO the receiver has to be stronger than that for you to hear anything

    Set the attenuator to zero. You will then hear fairly loud signal (if you find one) with a certain signal to noise, from sky noise and interference.

    Set the attenuator to 1.25 dB. You will hear the signal with the same copyiability only the volume will be less intense

    Set the attenuator to 4.5 dB. You will still hear the signal with the same copyiability only the volume will be reduced some more

    Set the attenuator to (in this example) to 7 dB. At this point the noise of your receiver is just as strong the input from the antenna, so the signal is very noisy as the receiver noise and the sky noise together swamp the signal itself.

    The last example shows that the mismatch loss (7dB)from a very high SWR (18:1)weakens the input signal from the antenna so it is below the noise level threshhold of the receiver. THIS is the case where a tuner would help.

    In most practical cases,a tuner adds no improvement to copyiability.

    73
    Chip W1YW
     
    N2OTG, K0WWX, K7ZGQ and 5 others like this.

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