What's the story with end-fed antenna's?

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KI7QVR, Feb 27, 2018.

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  1. WA7ARK

    WA7ARK Ham Member QRZ Page

    You (sort of) described a half wave wire, fed a couple of percent from one end, with a 1:9 turns-ratio transformer to step-up the impedance. Unfortunately, you picked the high-common mode current on the coax feed version.
     
  2. W5DXP

    W5DXP Ham Member QRZ Page

    I was assuming a husky common mode choke at the feedpoint - easy to do at 50 ohms.
     
    K9AXN likes this.
  3. AI3V

    AI3V Ham Member QRZ Page

    Outstanding!

    Just to be clear, no feedline or other wires connected to the "end fed"

    A battery operated tx, preferably internal batteries. If not, negligible wire length

    One guy claimes a .05 wl second element (counterpoise) so to be fair that configuration should be tested

    And, multi frequency claims need investigated.

    Rege
     
    KX4O likes this.
  4. W8IXI

    W8IXI Platinum Subscriber Platinum Subscriber QRZ Page

    Try it with an actual antenna and let us kow how it works for you.

    "It still could be true. Radiation from the two current maximum points on a full-wave CF wire interfere constructively broadside to cause the additional gain over a 1/2WL dipole. That's how MOM predicts the gain."

    And how did that work for you when you tried it with an antenna?
     
  5. W9XMT

    W9XMT Ham Member QRZ Page

    From Reply 153:
    However, a counterpoise conductor of any physical/electrical length and configuration converts a true end-fed antenna to an off-center-fed dipole with its feedpoint Z and gain much different than a true end-fed conductor without that counterpoise path.
     
  6. W5DXP

    W5DXP Ham Member QRZ Page

    That was the point of my above posting. The matching transformer or tuned circuit has an electrical length and that length appears to be the missing counterpoise.
     
    W3JJW likes this.
  7. K9AXN

    K9AXN Premium Subscriber QRZ Page

    I used a FWCF antenna for years on 20 Metres and yes it performed notably better than a 1/2 wave dipole. Fed it with a parallel tuned circuit with a center coupled link. It's counterpoise not Pool equalized.

    Regards Jim
     
  8. K9AXN

    K9AXN Premium Subscriber QRZ Page

    Cecil is right on this one. The fact that an inductor is composed of lump and distributed constants is the reason that plate RF chokes are misunderstood. In the case of the plate Choke the use of wl to characterize its reactance is grossly inaccurate. The designers of the past knew this and used the length of the wire to predict the first major series resonant point --- preferably above 30MHz.

    Regards Jim
     
    W3JJW likes this.
  9. WB2UAQ

    WB2UAQ Ham Member QRZ Page

    I tested a 1:64 transformer that seems to be all the rage. Many use the 1:49 but close enough. My interest has been just the transformer. This discussion might not have covered this. The loss comes in at about 1.1 dB for the FT240-43 core with a two turn primary and a 16 turn secondary all 16 AWG. I tested into a 3280 ohm resistor (3230 ohm metal film resistor plus a 50 ohm instrument on the ground end). I also made a second unit wound with 21 AWG. Its loss was identical to the one wound with 16 AWG. I then placed these back to back and measured the same loss (2.2 dB thru the pair). I also did a power test thru this pair at 100W. Both cores immediately became warm after about 3 minutes key-down. BTW I did the tests at 40 meters and tuned out the residual inductive reactance with a shunt C of about 185 pF (similar to what others are using but I measured the Z to see if this made any sense beforehand). The SWR was down to about 1.1 or better.
    I thought the loss would be pretty bad and was the reason I borrowed a few cores and ran the tests. I came up with a lower loss QRP unit based on a binocular core (BN-43-202 by Amidon or Fair-Rite Products). This one has a loss of about 0.5 dB and it was tested by a friend on 40 meters where he worked some French stations running 5W PEP from central New York state. 73
     
  10. AI3V

    AI3V Ham Member QRZ Page

    What I ment was both a actual end fed, that is zero length of the second antenna half, and also .05wl, as that is claimed by one manufacturer as being the magic length, never bothering to explain how a wire, of fixed physical length, remains a constant wavelength as frequency is varied.

    A ideal test would be a Altoids tin sized transmitter, operated by a internal battery, connected to the end of a 80meter band "halfwave end fed"

    Measure the field strength, locally, not skywave, then move the Altoids tin to the classic Hertz configuration and measure field strength again.

    Would everybody agree this proposed test would prove, or disprove the efficiency of the "end fed" vs center fed antenna?

    Rege
     

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