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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. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    If I want to increase readability of received signals in a noise-prone environment, I sometimes toss 50' of hookup wire out the window and use that as a receive antenna (almost laying on the ground, other than a few bushes) while transmitting with a real antenna.

    Signals may be 20 dB weaker, but if noise is 21 dB weaker, I improved reception.:)

    I do have a rotating small loop RX antenna ("Pixel") which works well for this as it can be rotated to null noise. I don't need S9 signals to work stuff, I just need some S/N ratio and headphones.
     
    WB9LUR, AA5BK and W1YW like this.
  2. W8ER

    W8ER XML Subscriber QRZ Page

    I can tune my tuner for minimum SWR using my transmitter. When I look at my panadapter, the grass level falls off on each side of the frequency that I just tuned it to. It's obviously acting as a bandpass filter. If I vary the tuner settings, the hump moves up and down the band and the SWR is lowest at the same frequency shown by the panadapter. Granted the visible passband is broad but centered on the frequency the tuner is tuned to.

    What I offered is an observation and my personal experience as an interested student of the hobby for 64 years. While I am not a college professor and hold no patents, my powers of observation are still quite keen. However, if you would like to explain why my observations are NOT valid, I am all ears!
     
    WN1MB and W5YZR like this.
  3. WM1A

    WM1A Ham Member QRZ Page

    I am all ears too. I have learned more by listening to Chip than anyone else
     
  4. VK3YE

    VK3YE Ham Member QRZ Page

    However I'd be wary of the tuner configuration circuit. Eg a pi network type tuner is basically a low pass filter. If your receiver is susceptible to overload from an AM broadcast signal on 1 MHz then it won't reject it by much (if anything). But if it was 27 MHz CB or FM broadcast signals overloading then it might.

    Whereas a T-match is a high pass filter better at rejecting lower frequencies.

    If you have an unselective front-end the best arrangement is likely 1 if not 2 tuned circuits to form a bandpass filter. However it will need re-adjusting for every 200 or 300 kHz you tune for best results. So you might have an in/out switch and switch it in only if needed.
     
    M0TTQ, WN1MB, W5YZR and 1 other person like this.
  5. DO1FER

    DO1FER Ham Member QRZ Page

    To find the correct impedance is what a antenna tuner is for. Especially for a homebrew antenna which is not really precise build. And the antenna vector analyzer shows where, on the different bands, the own antenna is usable too. In summary the tuner is just for to match light differences at the connection-point between the transceiver and the antenna, for to balance the resistance. That explains the difference of the signal strenght between the "pure" antenna and an antenna with a tuner.
     
    W5YZR likes this.
  6. W1YW

    W1YW Ham Member QRZ Page

    The video is about improving signal to noise, not rejection of out of passband signals and IMD (or PIM).

    Your point is a good one and no one rejected it(pun intended:). Not sure how you came to that conclusion. No one is putting you down. The objective is to share knowledge here, and no one is making you feel insecure.

    Most modern receivers (IN XCVRS)have excellent out of passband rejection (accomplished with various filter stages) so the NEED for a tuner to accomplish this is remote. It is an expensive and uneeded device for rejection --when-- already accomplished by the RX. Of course, in ham radio, few use separate receivers nowadays--its all XCVR.

    My IC-7800 has no change in the RX waterfall, beyond a baseline translation, when I put the tuner in and out. There is no practical additional rejection of IMD that I can see on the display. But this is because there are already several filter stages in the XCVR 's receiver.

    If rejection is really your issue then you should manually tune the tuner to maximally reject. This occurs when the SWR at the rejected signal frequency is very,very high, as set by the tuner. Most of the time that will NOT be at the tuner setting which gives you a conjugate match at the desired frequeny-- which is what the video is about.

    When you have a XCVR, the situation is determined by the TX setting on the tuner--best match at transmit-- and an RX 'rejection' tuner setting is irrelevant to this discussion.

    73
    Chip W1YW
     
    Last edited: Dec 21, 2021
    N9JLF likes this.
  7. W5YZR

    W5YZR Ham Member QRZ Page

    An intersting topic. I will monkey with my tuner exploring different bands and see for myself. My first thought on this subjuct was no but RF can be magical at times and their are so many variables to the RF equation that maybe it might. Thanks for presenting this subjuct.
     
  8. W4NNF

    W4NNF XML Subscriber QRZ Page


    It's simple and doesn't require a video to understand... Attach your receiver to a tuner. Note that as you near a match with the tuner audio...background noise, everything, increases. :)
     
    2E0TWD, PY2NEA and W1YW like this.
  9. W4NNF

    W4NNF XML Subscriber QRZ Page


    No magic. Not unlike a preselector on a receiver. ;)
     
  10. K6MIT

    K6MIT Ham Member QRZ Page

    you cannot raise signal strength without raising noise level also....
     
    2E0TWD, W4NNF and W1YW like this.
  11. SA1CKE

    SA1CKE Premium Subscriber QRZ Page

    Even if you increase both an overall stronger signal is easier to process. Some noise is wide band while the signal of interest is narrow band, and with a stronger signal overall it should be easier to filter.

    With a stronger signal you'd also get less influence from the local noise in the receiver.
     
    TIERONE and WN1MB like this.
  12. W5JAC

    W5JAC Ham Member QRZ Page

    Am I wrong that the reactance of the antenna causes a change in impedance at the antenna so the 50 Ohm coax now sees a mismatch at the antenna, the match between the 50 Ohm coax and the receiver isn't changed?
     
  13. W0AZ

    W0AZ Ham Member QRZ Page

    A truly fine, decades-experienced technician once quoted this familiar phrase to me: “In theory, theory and practice are the same thing. In practice, they are not.”

    (The technician was my Elmer, W9KV, the head of technical services at WBBM TV in Chicago, and I’ll leave aside for now his humorous observations regarding the differences between engineers and technicians.)

    This not because applicable theory is necessarily wrong; rather, it is because “in practice” theoretical discussion sometimes fails to account for all of the operative variables involved in the entirety of the particular “system” being discussed.

    The technician’s approach is to reason from theory as well as to believe (in this case) his ears.

    There are situations where the use of an antenna tuner will improve reception and discernment of the desired “signal” above noise, and situations where it will not, and the reasons for this are complex and multi-factorial.

    Inordinate theoretical focus on any one or two factors often fails to account for the complexity of the phenomenon.

    In this case, “Trust your ears.”
     
    K3RW, TIERONE, WN1MB and 4 others like this.
  14. W1YW

    W1YW Ham Member QRZ Page

    Look at an antenna feedpoint as a 'sampling point' of a sine wave (on the antenna). The sine wave doesn't changed by being 'sampled' (assuming the feedline is choked and does not become part of the antenna). What a tuner does is match the imepdance of that 'sampled' point to a 50 ohms-real impedance.

    IOW, as you say, nothing changes from the antenna standpoint. IOW the noise you receive at the antenna,and the signal you receive at the antenna--at a given frequency-- are 'locked'. All a tuner can do is make sure the overall antenna input voltage to the receiver is stronger than the noise of the receiver itself, by matching.

    Because most receivers are very quiet themselves--very little receiver noise--you need a huge mismatch loss from a very high SWR to enter into that special circumstance of the tuner improving the overall signal to noise..

    73
    Chip W1YW
     
    Last edited: Dec 21, 2021
    SA1CKE likes this.
  15. W1YW

    W1YW Ham Member QRZ Page

    No thanks.

    I will trust my brain. And the knowledge base of hard won understanding of electromagnetics, by thousands of people. from the last 150 years.

    The physics of these conditions is well known. A tuner in a conjugate mode--not a filter function; not a preselector function; not a notch function-- is incapable of increasing the SINR of a signal from the antenna. Not theory: its a fact.

    This video makes the incorrect assertion that taking a tuner at conjugate improves SINR from the antenna. Nope. Not possible. Matching impedance does not change the incoming sampled wave from the antenna, at the conjugated frequency.

    Why listen to me? Do some reading; think it through for yourself.

    73
    Chip W1YW
     
    W4NNF and PA0MHS like this.

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