The EFHW Transformer Redefined

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by AF7NX, Jul 22, 2021.

Tags:
ad: L-HROutlet
ad: l-rl
ad: MessiPaoloni-1
ad: abrind-2
ad: L-Geochron
ad: Left-2
ad: Left-3
ad: L-MFJ
ad: HRDLLC-2
  1. AF7NX

    AF7NX XML Subscriber QRZ Page

    The End-fed Half-Wave antenna has become popular in recent years because it is easy to deploy and is resonant on several bands. The key to this antenna, a "box" which contains a step up transformer, has been copied blindly many times. A new approach presents a less expensive, smaller, lighter, and more efficient device by carefully limiting leakage inductance and by heat-sinking smaller ferrite cores to an aluminum case.
    [​IMG]

    See Engineering the EFHW 49:1 Transformer and Antenna at SquashPractice.com
     
    KX4O, W6JJZ, M0TTQ and 1 other person like this.
  2. WA7ARK

    WA7ARK Ham Member QRZ Page

  3. W6JJZ

    W6JJZ Premium Subscriber QRZ Page

    Lest this thread not get the attention it deserves, I'll offer one of my rare QRZ comments--

    I've been following the work on EFHW antennas and transformers for a long time now. A lot of it is repetitious (or largely so), but some breaks new ground--Owen Duffy's posts on his blog on core geometries and winding configurations come to mind. IMHO, AF7NX's article (referenced in his posting) similarly falls in this latter group. (Among other things, I think he answers WA7ARK's question.) Anyone interested in EFHWs should also look at the article he did a month ago--

    https://squashpractice.com/2021/06/23/performance-of-491-ferrite-core-transformers/

    They are both well worth reading.

    Charlie, W6JJZ
     
    AB1YW likes this.
  4. K7JOE

    K7JOE Subscriber QRZ Page

    "The End-fed Half-Wave antenna has become popular in recent years because it is easy to deploy and is resonant on several bands. The key to this antenna", just like any antenna, is not the transformer, however. It is to get the antenna wire up as high as possible and in the clear.

    With modern ferrite material cores using similar mix recipe being used by ALL the transformer designs, the minutiae variation in transformer design due to winding ratios and additions of capacitors to tune out inductance does not result in many new fangled breakthrough.

    All of these transformer-matching antennas will still perform poorly if the radiating wire is not mounted high and in the clear.... no matter what secret sauce is claimed to be inside the black-box.

    Further, no ferrite-core transformer -based antenna works perfectly across all ham bands. They are all (windings, core mix) a compromise to cover multi-bands of some fashion or another. One thing, however, is consistent with ALL these antennas : get the wire higher, the performance improves on every band.

    Studying the charts further reveals the difference in most cases between winding approaches is but a fraction of a dB for most frequencies ... in a worst case scenario the loss is less than 1.5 dB between best to worst ...hardly noticeable in most HF applications where feedline loss, signal to noise ratio due to common mode currents on end-feds, and even common mode induced alterations of the rf radiation pattern can cause far bigger issues than a 1.5dB loss.

    Now, If you're worried about every last dB...an end fed antenna should not be used in the first place -- after all, they are a compromise introducing a (lossy) transformer for matching on bands other than the fundamental frequency. In a single band situation, the losses are negligible and efficiency approaches that of a regular dipole antenna (98-99% as efficient). So then, the only real variant is getting the antenna wire high enough above earth so as to reduce ground losses.
     
    AD5HR and WA7ARK like this.
  5. W6JJZ

    W6JJZ Premium Subscriber QRZ Page

    No one (I hope) questions that higher is generally better, but what's the evidence that an EFHW is less efficient on harmonics than on the fundamental frequency? I'm not aware of it, but perhaps I've missed something.

    Charlie, W6JJZ
     
    KU3X likes this.
  6. KU3X

    KU3X Ham Member QRZ Page

    I deleted my comment. Sorry

    Barry, KU3X
     
  7. K7JOE

    K7JOE Subscriber QRZ Page

    By virtue of the fact that there is typically higher VSWR on the harmonically related bands, and as the paper above describes, there are variations in loss parameters based on the type of transformer winding approach you are using- some bands will be more efficient than other bands - it is easy to deduce that A) feed line loss (due to higher vswr) and B) inefficiency in the transformer make for less efficiency on the harmonics compared to the fundamental frequency for which the antenna is designed.

    Finally, we know the funny lobe characteristics when using an antenna on a harmonic of the fundamental frequency. There are peaks and nulls in the radiation pattern and this can be a "perceived" loss (or gain) if the antenna happens to be oriented such that the null and peak are in the wrong place(s).
     
    Last edited: Jul 25, 2021
  8. KU3X

    KU3X Ham Member QRZ Page

    The lowest SWR on 40 meters on my HWEF40 is 1 to 1. On 20 meters, it's also 1 to 1. I also did a comparison between my HWEF40 against a coaxial fed half wave antenna, using reverse beacon and on both 20 and 40 meters, they both performed exactly the same.
    Barry, KU3X
     
  9. K7JOE

    K7JOE Subscriber QRZ Page

    Electrically isolated end-fed vs. center-fed dipole radiation (hamradio.me)

    Interesting -- some analysis indicates approx 1.5 dB difference between an EFHW and a classic dipole

    Just the same to my earlier post, in most cases due to band propagation conditions, a 1.5dB difference is hardly noticeable in all but the most ideal situations and conditions.

    How does the antenna perform on 10M, say, in the CW portion of the band ?
     
  10. W6JJZ

    W6JJZ Premium Subscriber QRZ Page

    I don't find evidence for either generally higher SWR or lower transformer efficiency on harmonic bands in the paper nor in his earlier paper (if anything, the reverse is sometimes true), nor in my own experience with an EFHW. That's putting aside 10 meters, where efficiency often drops with #43 core material. As for lobes in patterns, that's another issue. Sometimes they are beneficial, sometimes not, depending on the route. I hope no one questions that.

    Yes, if you can put up a c.f. resonant dipole, do so. Probably ditto for a doublet if you want multiband operation. All different issues

    My initial post was intended to urge folks to read the two papers. I stand by that.

    Charlie, W6JJZ
     
    Last edited: Jul 25, 2021
    KU3X and KX4OM like this.

Share This Page