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Wondering why this antenna isn't more popular....

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KC3RN, Feb 8, 2019.

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  1. WD4IGX

    WD4IGX Premium Subscriber QRZ Page

    Actually yes, it does. Differently than when dry, but it's never been a problem. I've run it in torrential rain, with snow piled on it, all kinds of things.

    You've mentioned him before. And I'll repeat - one anecdote != evidence. If it blows around too much in the wind then 1) it's probably too slack, and 2) put a twist in the line every few feet, and take a small rope or heavy cord and run between the two points where it sways, threaded through the spacers (or window openings) and secure that at each end. Problems solved.

    HAVE YOU EVER TRIED IT?

    Look, I don't care if you do or not. Means nothing to me either way. But you are being dismissive and derisive about something you seem both uninformed and inexperienced with.
     
  2. WB5WPA

    WB5WPA Ham Member QRZ Page

    @WD4IGX

    Look, it's got its place, but, sometimes stalwart, white knight 'defenders' of open wire line over-prescribe and over-recommend it.

    I run antennas for the most part that require -no- antenna tuner in the shack so I can run shoe-string sized coax out to the antenna and experience little to no loss ... the rest of you, like yourself, haven't reached this pinnacle of perfection yet, so must resort to compromise methods to achieve similar results by keeping line losses low through the use of technology that has a small 'host of issues' as previously listed.
     
  3. W4EAE

    W4EAE Ham Member QRZ Page

    I would be curious as to how this http://www.hamuniverse.com/wc7iswr.html is wrong. It is long, so I will sum it up. It basically states that a non-resonant antenna tuned with an antenna tuner is resonant, less coax losses. It surely does actually work better than a non-resonant antenna. This can easily be observed without ever even transmitting. Connect a non-resonant antenna to your radio and see what you can hear. Tune it up and everything--noise, received transmissions--will be louder and more readable. If you had not tuned that metal windows frame, you probably could not have worked France.

    I am not trying to discredit you, its just that I see hundreds of people saying this when the science and basic experience suggests otherwise. :)
     
  4. WB5WPA

    WB5WPA Ham Member QRZ Page

    Let's see, we have these conditions that exist regarding an "antenna" (a piece of wire used to catch or radiate RF energy) then:

    (1) Intrinsically resonant (e.g. a 1/2 wave dipole providing a match to coax directly), vs

    (2) non-resonant (w/o assistance from a tuner; just plug-the-wire-into-the-radio's jack. Who knows what the Z and resulting mis-match of this configuration is!) vs

    (3) impedance matched (meaning, maximum power transfer is achieved, whether that is during receive or transmit. This usually means bringing the wire into resonance via additional capacitance or inductance applied TO THE WIRE through perhaps some length of lossy coaxial cable OR sometimes the 'matchbox' is located right at the 'antenna wire'.)

    (The foregoing excludes 'active' antennas like broadband loops or E-probes.)
    .
     
    WA7ARK likes this.
  5. AA7EJ

    AA7EJ Ham Member QRZ Page

    These SWR "discussions"
    These SWR "discussions", the above referenced included, do not explain why would anybody wanted to measure SWR BETWEEN rig and an antenna matching device and subsequently evaluate / judge the whole system by such measurements.

    It may be customary to use term "antenna tuner', but as already demonstrated here and many times over - very misleading term.
    ( Antenna SYSTEM can be matched by other means also. )

    Especially when "SWR" , using whatever convenient definition author prefers , is a result of impedance mismatch at the antenna which irregardless of "definition" does not change when "THE ANTENNA SYSTEM" is "MATCHED".
     
  6. WA7ARK

    WA7ARK Ham Member QRZ Page

    I just happened to be reading some of L. B. Cebik W4RNL(SK)'s material on the wayback machine and encountered this quote:

    "One of the dangerous sound-bite ideas that pervades amateur radio practice is that the losses in a parallel feedline are so low that its length and the SWR mismatch between the line's characteristic impedance and the antenna terminal impedance do not matter. The line will provide a high-efficiency power transfer from the equipment to the antenna system (or vice versa on receive) regardless of the line length or the mismatch. Unfortunately, this sound bite is only correct up to a point. Like any feedline, even the 600-Ohm open ladder line has a baseline matched loss value per unit of length. A mismatch creates additional loss such that the SWR acts as a multiplier on the matched loss value. The higher the SWR value, based on the mismatch between the line characteristic impedance and the antenna terminal impedance, the greater will be the losses on the line."
     
    ND6M and WB5WPA like this.
  7. WA7ARK

    WA7ARK Ham Member QRZ Page

    Because the SWR along the feedline is what causes losses in the feedline.
     
  8. W4EAE

    W4EAE Ham Member QRZ Page

    I refer here to 'match' as opposed to 'antenna tuner.' ;)

    Please correct me if I am wrong, but my takeaway is that reflected power when it is returned from the antenna to the match is re-reflected back to the antenna; making the only loss in a matched, initially non-resonant antenna the losses incurred from the energy traveling down the feedline, back to the match, and back to the antenna.

    Supposing you are using 100ft of RG8 and transmitting 100w on 20m.
    Your line loss to a resonant antenna is is 14w. Power delivered to the antenna is 86w.
    If initial SWR is 3:1, then reflected power would be about 20w. Power delivered to the antenna is 66w.

    With a match in place, 17w of the initial 20w reflected would be sent back down the feed line.
    The loss back down the feed line to the antenna would be 2.5w.
    Final power delivered to the antenna would be 66w+14.5w: 80.5w

    80.5w is more than 66w. In fact 80.5w is near as makes no difference to 86w, particularly in comparison of 66w.

    A resonant antenna is slightly better than a matched antenna, and both are significantly better than a non-resonant antenna.

    If this is correct, then my original argument--that an antenna match does do a lot more than 'make your radio happy' is correct.
     
  9. WB5WPA

    WB5WPA Ham Member QRZ Page

    ALL this 'SWR' talk could be better understood IF ppl understood VARs (Volt-Amperes Reactive) terminology and how that applies from the power generation, transmission and distribution field *to* the field of transmitters, RF transmission lines and antennas.

    The purpose of the antenna 'tuner' is to apply a correction (as well as maybe an impedance transformation) in the form of VARs (capacitive reactance OR inductive reactance) between the transmitter and the antenna (ignoring Impedance matching, like 50 to 75, or 50 to 300 Ohms for the moment.)

    IF you supply those VARs *to* the antenna (through the length of the RF transmission line) the additional corresponding currents (and perhaps voltage 'loops' or peaks as well) that exist (because the added VARs) on the RF transmission line will cause ADDITIONAL LOSS in said RF transmission line ...

    This is not a perfect 1:1 analogy, but it goes a LONG ways in demonstrating the losses that are seen owing to reactive RF currents and voltages that will be present on the RF transmission line, whether it is open wire or coaxial line.
     
  10. W5DXP

    W5DXP Ham Member QRZ Page

    Actually, in a low-loss antenna system, the impedance mismatch at the antenna feedpoint is neutralized by a conjugate match at that point. For simplicity, let's assume a relatively short run of 50 ohm hardline coax and a relatively low SWR such that the coax losses can be ignored. The tuner is adjusted so the XMTR sees 50 ohms, i.e. achieves a 50 ohm Z0-match at the tuner input with an SWR of 5:1 on the hardline.

    XMTR----TUNER------50 ohm hardline------100+j116 ohm antenna feedpoint impedance

    Now we change the configuration so we can measure the impedance at the antenna feedpoint looking back toward the tuner.

    50 ohm resistor---TUNER------50 ohm hardline------Antenna Analyzer

    The antenna analyzer will read 100-j116 ohms indicating that the +j116 ohm reactance has been neutralized and the 100 ohm resistance matched by the conjugate match at the antenna feedpoint. That's the necessary and sufficient condition for maximum transfer of available source power according to the maximum power transfer theorem. The 50 ohm Z0-match at the tuner input meets the IEEE definition for system "resonance".

    Moral: In a low-loss antenna system, if a (near) conjugate match is achieved by a Z0-match at the tuner input, an impedance mismatch at the antenna feedpoint (and therefore the SWR) doesn't matter unless the system losses are unacceptable. Transmission line losses can be estimated using TLDetails available from AC6LA.com. What value of losses are "unacceptable" will differ among individual hams.

    Sorry, you only took one reflection into account. 1/4 of that 14.5 watts will be reflected by the mismatch and make another round trip. Theoretically, there are an infinite number of round trips.
     
    Last edited: Feb 11, 2019
    K7TRF likes this.

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