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Hamstick or base loaded 8' whip?

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KK4NSF, Jan 11, 2019.

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  1. W5DXP

    W5DXP Ham Member QRZ Page

    Sounds like your measurements were made on the electric field in the near field. Field strength measurements need to be made in the far field, i.e. quite a few wavelengths from the antenna. That was done for the 80m shootout results.
     
  2. KC8VWM

    KC8VWM Ham Member QRZ Page

    I did some F/S tests "at a random distance" with the limitations of visual sight and yes I admit this was not conducted in a controlled measured environment, nor was the equipment adequately lab calibrated. However, I don't feel that completely dismisses my material baseline observations.

    Any way you look at this, the concept of a short antenna is still a short antenna and it's not going to be the epitome of antenna efficiency wouldn't you agree?
     
    Last edited: Jan 12, 2019
    KG7QJB likes this.
  3. K6UJ

    K6UJ XML Subscriber QRZ Page

    W5DXP hit the nail on the head. The field strength readings are meaningless when taken in the near field. The 80 meter shoot out tests are done from the far field and are credible. I recommend reading the excellent published article by N0AX and K7LXC that was first present at Dayton "HF Tribander Performance Test Methods and Results " Very good overview of how to do the field strength testing the right way.
    Bob
    K6UJ
     
    NH7RO likes this.
  4. KC8VWM

    KC8VWM Ham Member QRZ Page

    Really, I can assure you I don't need any schooling on how to properly conduct a f/s test thanks.

    I only accurately described what was actually done while I was at a public park with a few antennas and a portable radio given the situation and presented limitations at hand, so try to avoid reading into everything any more than that.

    So no, this measurement testing was not conducted in a controlled test environment using any lab calibrated test equipment and just to be clear, I have no intention of conducting any further testing in any controlled test environment in the foreseeable future so far.

    I was merely providing my own conclusions based on my own personal observations while comparing some antennas, nothing more. You may choose to agree with these conclusions, disagree, or feel indifferent ...it's really your call.
     
    Last edited: Jan 12, 2019
  5. K6UJ

    K6UJ XML Subscriber QRZ Page

    The ARRL is a great resource for how to conduct viable field strength measurements also. It doesn't take lab equipment or a controlled test environment.
     
  6. AA5CT

    AA5CT Ham Member QRZ Page

    From: https://www.qsl.net/g3pto/mobant.html "Effective HF Mobile Antennas by Keith WB2VUO"

    Excerpt (fair use copyright extract):

    Loaded antennas fall into three categories, Base-Loaded, Center-Loaded and Continuously-Loaded. The Base-Loaded antenna is the easiest to construct with the tools available to the "average" ham, but shows a lower efficiency than the other designs. ...

    The radiation resistance of the 8-foot whip falls in a very low range, running from 0.08 ohms on the 160 Meter band to 16.1 ohms on the 12 Meter band as shown in the table below.

    Effective HF Mobile Antennas by WB2VUO_Rr 8ft whip.jpg
     
  7. AA5CT

    AA5CT Ham Member QRZ Page

    These guys took an interesting approach to measuring the field strength from a mobile HF antenna system mounted on a vehicle - they made observations from atop a several story building (they wished to measure the higher "take-off angle" as they say):

    https://www.w0qe.com/shootout_2011.html
     
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  8. W5DXP

    W5DXP Ham Member QRZ Page

    Charles, all I am saying is that one of the conclusions made based on your measurements seems to contradict our shootout results which agree with the data on mobile antennas in The ARRL Antenna Book. Taking an 8 ft 80m mobile antenna, for instance, the base loaded version has a radiation resistance of 0.35 ohms and a feedpoint resistance of 16 ohms for an efficiency of 0.35/16 = 2.2%. An 8 ft. 80m center-loaded mobile antenna has a radiation resistance of 0.8 ohms and a feedpoint resistance of 22 ohms for an efficiency of 0.8/22 = 3.6%. That correlates fairly well with the 3dB advantage of the center-loaded antennas over the base-loaded antennas measured in the 80m mobile shootouts and it is also extremely obvious that a short antenna is "not going to be the epitome of antenna efficiency".

    The radiation from a standing wave antenna is highest where the acceleration of the charged particles is highest and for most mobile antennas, that is at the feedpoint. The longer we make the straight high current portion of the antenna under the loading coil, the greater the radiation. Contrary to The ARRL Antenna Book, the coil has a large effect in reducing the amplitude of the current and thus reducing the acceleration of the charged particles. The reason that the coil doesn't radiate much in spite of the high current is that the fields tend to cancel because the current in one side of the coil is traveling in the opposite direction from the current in the other side of the coil (somewhat like a transmission line).

    P.S. I agree with The ARRL Antenna Book when it is correct and disagree when it is incorrect.:rolleyes:

    [​IMG]
     
    Last edited: Jan 12, 2019
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  9. NH7RO

    NH7RO Ham Member QRZ Page

    I know center loading is always better than base-loading but Isn't top-loading the best of the three? Please correct me if I'm wrong.
     
  10. KC8VWM

    KC8VWM Ham Member QRZ Page

    Base loading has more mechanical installation advantages and top loading has more signal performance advantages.

    Choosing one configuration is always going to be a compromise over the other.
     

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