Current distribution on / in NOT in center fed antena

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by AA7EJ, May 12, 2019.

ad: L-HROutlet
ad: l-rl
ad: L-MFJ
ad: Left-3
ad: Left-2
ad: Subscribe
ad: MessiPaoloni-1
  1. W9XMT

    W9XMT Ham Member QRZ Page

    That is rather clear, based on your responses.

    Maybe with more study of my comments and graphic, you will come to realize the value in them as a very useful means to measure the performance of those antenna systems.

    73.
     
  2. AH7I

    AH7I Ham Member QRZ Page

    You respond to a post about current in short dipoles with an experiment using a wire that is over a wavelength long.
    I'm just curious as to what happens with the same experiment and a short ( short << wavelength) wire.
    -bob
     
  3. AH7I

    AH7I Ham Member QRZ Page

    You did not answer when I asked about l and d.
    You refer to a wire, then a disk, now the earth.
    If you could please be more specific what you are referring to when using the same variable for different scenarios...

    Are you a robot?
     
  4. K9AXN

    K9AXN Premium Subscriber QRZ Page

    Yes, ….. am a robot ….. I will carry your message to Jim ………………. Jim told me to tell you that you are to go to your father and tell him that he wants to speak to you!...………………………………. are you there? .…………. I will inform Jim that you no longer exist. Humans seem to have a bunching problem with their under garments ………. I'm so happy to be a robot …….. Jim has informed me that if you should re-awaken tomorrow in a sustainably pleasant state of mind he will speak with you. erk zlpahd54363 Zianara …. Robot for night night
     
  5. W9XMT

    W9XMT Ham Member QRZ Page

    My analysis of that concept was included in Reply 27 of this thread. That analysis is repeated below, and underlined.

    "That r-f pulse signal tested that antenna system over the entire r-f bandwidth it uses, and eliminated off-channel 'media' responses such as at d-c/0 Hz, which only pollute the measurement, and are meaningless to the performance of that antenna system."
     
  6. K9AXN

    K9AXN Premium Subscriber QRZ Page

    With that experiment, I was trying to explain exactly what surge impedance and surge current was and it's properties. I asked a simple question, Do you find anything wrong with the explanation of the results i.e. Does it violate Kirchoff, Ampere, and does it properly explain the properties of Surge or displacement current and surge impedance. It specifically tests the Zo and velocity factor of coax, twin lead, and a single straight wire and it does it accurately. The velocity factor and length of time it takes the pulse to return provide the electrical length for a resonant wire. If I had sent an analog RF pulse into the wire the transit time would be the same. I never said anything about a system of transmission lines. It is a simple experiment that anyone can do. It provided Shirley with the answer requested. Did anyone else take the time to do so??? Is 54' a short antenna? Shure for 160 Meters ---- for 2 Meters you answer that.

    The information that you provided was totally inadequate to describe anything. What frequency, what transmission line combinations, Was the RF pulse one frequency, AM, FM, carrier, multiple frequencies, or anything. What was the test to accomplish or what were you looking for? Was it simply loss? Was it looking for modulation disturbance?

    I'll have to write it off to Maybe I'm light in the loafers and that's OK

    As a friend, I say please have a great night

    Regards Jim
     
  7. W9XMT

    W9XMT Ham Member QRZ Page

    The carrier frequency is shown at the bottom of the report page graphic in Reply 21 of this thread (531.26 MHz).
    The transmission line was ~ 1500 feet of 6-1/8" OD, 75 Ω, rigid coaxial line (20-ft sections).
    The 531.26 MHz carrier was amplitude-modulated by a video pulse having sin² rise/fall times of about 0.25 µs. The video spectrum of that pulse contains energy out to about 4 MHz, and replicates the video frequencies, amplitudes and bandwidth of an analog TV signal.
    This waveform spectrum and measuring technique determined the return loss of the incident pulse for that antenna system, e.g., the amount of incident r-f energy that was radiated vs. returning to the source (transmitter).
     
    Last edited: May 28, 2019
  8. K9AXN

    K9AXN Premium Subscriber QRZ Page

    Thanks Richard,

    I was trying to make it much more complex that it is. My post was directed at understanding the antenna wire logic ---- had nothing to do with the effects of modulation or transmission line losses. It would be unusual to try to explain antenna theory by integrating the entire system all the way beck to the ground on the transmitter and matching circuits --- might be confusing.

    What does that have to do with measuring the surge impedance and velocity factor of a wire antenna using a DC pulse to determine the electrically resonant frequency and the radiation resistance??? They are precise and accurate measurements using a DC pulse.

    This is not directed at you Richard, but to the cranky ones:
    The experiment is a great teaching tool that can be done in practically any Ham shack. Why try to poison any attempt to generate interest in a fading hobby. That experiment can distinguish lumped properties from distributed and be an intro to understanding displacement current and relativity.

    We've all had our day in the sun --- Sharing the actual knowledge and logic of electronic properties with others gives them the ability to think for themselves and enjoy the satisfaction that accompanies it. All to often one of the thought to be authoritative figures vomits a set of equations then says "There you go, I know what I'm talking about", until you ask "please explain the logic". Then it gets very quiet.

    If a person is perceived to be authoritative, they have a responsibility to behave so and say I don't know but will find a way to explain the concept, not mindlessly use a CAD tool to do the thinking then say "I designed this thing". No, the person is a clerk that fed and bathed the computer so that it would continue to do the thinking for him.

    Have a good day

    Regards Jim
     

Share This Page