Don't Earth a counterpoise ?

Discussion in 'General Technical Questions and Answers' started by M6LVC, Dec 1, 2016.

ad: L-HROutlet
ad: l-rl
ad: Left-2
ad: Left-3
ad: Subscribe
ad: FBNews-1
ad: L-MFJ
  1. KK4YWN

    KK4YWN Ham Member QRZ Page

    i have to give up on you at this point.
     
  2. AH7I

    AH7I Ham Member QRZ Page

    Darn! I would really like to know how to get more power out of one side of a source than the other.
     
  3. AH7I

    AH7I Ham Member QRZ Page

    We have no I at the end of the antenna because it has no place to go. We have no V in the middle because all the energy is in the form of current. It's only the current that radiates. It's only the current that results in I^2R loss. An antenna is not a motor. A motor works because of opposing magnetic fields. These are caused by current. The REAL work from a motor is based on the currents. Because they are shifted from the voltage by inductance in the motor, we can not measure this work by P=IV.
     
    Last edited: Dec 18, 2016
  4. AA7EJ

    AA7EJ Ham Member QRZ Page

    "We have no I at the end of the antenna because it has no place to go."
    Assuming this is correct, that is way I keep wondering about the dependency of "current distribution " on 1/2 wavelength "radiator" as initially demonstrated in this thread.
    In my view that sinusoidal (!) curve is independent of applied frequency and length of such "radiator".
    It should reflect the actual transfer of energy from electrical to electromagnetic.

    If my simplistic view is correct - the current could be zero before it reaches the end of its path just due to real conversion of energies.

    In my view we need to differentiate between actual (dynamic) generator supplied standing wave - in time - and theoretical current distribution - (static) in space.

    My head hurts.

    73 Shirley
     
  5. AI3V

    AI3V Ham Member QRZ Page

    If you can get a hold of an antenna analizer you can experiment with different length radiators and transformer ratios.

    You will get a better feel how the harmonic relationship of our bands conspire to prevent a perfect matching solution across the HF range.

    I used and repaired several types of wideband HF antennas when I was stationed in the British Indian Ocean Territory (Diego Garcia Where I repaired 40000 watt HF transmitters and operated as VQ9AA)

    To my knowledge there are only 3 real broadband antenna setups possible that will provide a better than 2:1 vswr from 3-30 MHz

    The inverted discone- 60 vertical 1/4 wave @3mhz wires in a 60 degree cone fed against 120 1/4 wave @3mhz ground wires.

    The dual nested 3 wire rhombics. Iirc they were 600 feet on each side, about 100 feet up.

    And two types of log periodic antennas, a 7-30 MHz horizontal lp, rotatable at about 120' and some "sector" vertical log periodic arrays that were about 20 or so vertical radiators with a 1/4 wave high @3mhz tower in the center with 4 log arrays nsew

    All of these antennas were electrically simple, and mechanically heroic. Total copper content of each antenna was measured in miles of wire and hundreds, even thousands of pounds.

    Tldr: they were bloody huge antennas.

    Rege

    The US NAVY has published a fantastic course called NEETS, navy electricity and electronics training series. Module #10 has a wonderful explanation how practical antennas and transmission lines behave.
     
    Last edited: Dec 20, 2016
  6. AH7I

    AH7I Ham Member QRZ Page

    The current distribution depends on the frequency and the shape of the antenna.
    It does. Only a good bit of that electromagnetic energy in a resonant antenna is stored in the reactive field.
    I think you may be confusing current with the current distribution.
    73, -Bob
     
    Last edited: Dec 20, 2016
  7. AA7EJ

    AA7EJ Ham Member QRZ Page

    I think you may be confusing current with the current distribution.

    Yes and no.
    I just want some explanation of these statements:

    "We have no I at the end of the antenna because it has no place to go."
    "antenna radiates ...because of the open end " - this is NOT direct quote

    If the first is statement is correct - radiator of ANY length , hence my argument of static current distribution is independent of frequency, would still have similar current distribution DIFFERENT from standing wave.
    Hence full wavelength radiator current standing wave ( time domain ) would be different than this current distribution I refer to as static - space domain.
    Generator supplied current can be sampled /visualized in discrete intervals (time domain ) along the radiator,
    current distribution (space domain) is a absolute graphical display of each of these samples in the radiator and reflects the actual process of transferring energies.

    Maybe I am hung up on terminology and we can just agree that current flow in radiator transfers to the electromagnetic energy and be done with this thread,

    73 Shirley
     
  8. AH7I

    AH7I Ham Member QRZ Page

    There are no charge carriers beyond the end of the antenna.
    I don't know where this "NOT direct quote" comes from.

    Look at the current distribution on a 1/2 wave dipole excited at resonance. Now excite it a 3 times the frequency. What does the current distribution look like?
    The radiation is a maximum where the current is a maximum.
    The current we are talking about is charge moving back and forth in the wire.
    The current distribution represents the amount of charge moving back and forth.
    For our half wave antenna, it's a maximum at the source and zero a quarter wave away. For our 3/2 wave antenna, it's a maximum at the source, zero a quarter wave away, maximum a half wave away, and zero again a the end, 3/4 wave away.
    We still can't feed a 1/2 wave antenna from one end without a balancing current somewhere(common mode, earth, counterpoise, ...) else.
     
  9. AA7EJ

    AA7EJ Ham Member QRZ Page

    "For our half wave antenna, it's a maximum at the source and zero a quarter wave away.

    We still can't feed a 1/2 wave antenna from one end without a balancing current somewhere"

    The above statements contradict each other - maximum current at source which would include end if we "balance the current elsewhere".

    " Look at the current distribution on a 1/2 wave dipole excited at resonance. Now excite it a 3 times the frequency. What does the current distribution look like?"

    That is not what I am concerned about - that is a generator current DISPLAY on the radiator in TIME DOMAIN, which I have been saying from get go.

    Sorry , this thread is going nowhere, I am outa here.

    73 Shirley
     
  10. KR6AUL

    KR6AUL XML Subscriber QRZ Page

    Just when I think I am starting to understand, I read a post like this and I am back to square one. I will get it, I will get it...give me time.:confused:
     

Share This Page