Antenna Analyze, or System Analyze?

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by CHUCKSTEIN, Oct 8, 2021.

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  1. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    It's difficult to define source impedance as it will vary with frequency (even the slightest change) and power (even the slightest change).

    "Most" low power transmitters (e.g., below broadcast-station levels which are generally in kilowatts) are design optimized for a 50 Ohm resistive load, but that doesn't mean that with varying conditions their source impedance is actually 50 Ohms.

    Real antennas that aren't purely resistive loads vary in Z with frequency (even the slightest change), so will typically only exhibit VSWR = 1.0:1 at exactly one frequency. That doesn't mean they don't work fine over a range of frequencies.

    A good way to measure how they're actually working is using field strength readings.

    I've worked on many MF-HF commercial broadcast station sites and can't remember any of them that had resonant antennas. There may be some, somewhere but I've never seen one. That's why they all have antenna tuners at the feedpoints.
    PU2OZT likes this.
  2. KE0NSK

    KE0NSK Ham Member QRZ Page

    I did say resonant in a prior post when I meant efficient. That was wrong, but the results are still true for an antenna fed with any amount of feed line. The vswr dip is the absolute best method for 99.5ish% of hams to know where there antenna system is most efficient. Granted, a field strength meter 10 miles away would be an interesting option, but take off angles and lobes could lead one astray if not careful.
  3. W9IQ

    W9IQ Ham Member QRZ Page

    What part is not true?

    - Glenn W9IQ
  4. KE0NSK

    KE0NSK Ham Member QRZ Page

    Why in the world would I take that bait?
  5. W9IQ

    W9IQ Ham Member QRZ Page

    Ok, I will leave it to others to point out my error(s).

    - Glenn W9IQ
  6. KE0NSK

    KE0NSK Ham Member QRZ Page

    It's not errors, it's just ridiculousness. If I say than an antenna fed with coax is most efficient at the vswr dip. You say no, the antenna SYSTEM is efficient at the dip! We have established that you aren't stupid, so whatever your reasons are to argue dumb points.. it's not my problem.
  7. W9IQ

    W9IQ Ham Member QRZ Page

    It wasn't my purpose to get you worked up. I am sorry that happened. Please accept my apology.

    But at the same time consider that technical discussions involve terminology that if not applied correctly, can lead to erroneous conclusions. Lot's of people use this site for reference...

    - Glenn W9IQ
  8. KE0NSK

    KE0NSK Ham Member QRZ Page

    Even with my mistake, the conclusion is the same, and you know this is fact. There was a time when I was striving to know every detail about antenna theory. One day I read a single paragraph of "Reflections" and it turned my world upside down. VSWR is really the key to tuning a proven antenna design that falls within the expected tolerances that we know by modeling (or googling others work.) VSWR can tell me if my 1/4 wave vertical can be efficient, and on what frequency that efficiency is maximized.

    Edit; I do give you credit for not twisting "the dip" into "a dummy load must be efficient because it has low swr's."
  9. WE4E

    WE4E Premium Subscriber QRZ Page

  10. KE0NSK

    KE0NSK Ham Member QRZ Page

    Lol, it's so simple it seems absurd. I promise you will probably understand some day.

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