Most Efficient Antenna for QRP

Discussion in 'QRP Corner' started by W7CJD, Dec 15, 2015.

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  1. W4KJG

    W4KJG Subscriber QRZ Page

    I still don't have all of the results from my testing, and I still have some testing to accomplish, but I sure have been surprised by the results I've experienced over the last couple of weeks after building several of these:

    I'm taking a break from testing them against an approximate 137 foot doublet at about 35 feet above earth, and a 21 foot base loaded vertical over a ground plane of sections of chain link fence laying on the ground.

    I still don't believe what I'm seeing for impedance at the end of the line, and what I'm hearing on the non-WARC 80-10 meter bands. I feel like I have hit some simple "magic" antenna that will go "poof" when I wake up. There seems to be a lot of others who have also found similar results. I don't want to promote competitors to QRZ, and I especially don't want to promote those who have taken advantage of the initial design and the many kits made available by the Emergency Amateur Radio Club of Hawaii.

    But, if you "Google" the term "EZ WIRE END FED ANTENNA" or "EARCHI Review" you should find what I'm talking about.

    I spent several hours last night changing the radiating element lengths and 4-wire and 8-wire ground plane/radial lengths, including removing the ground planes completely from the area. For the latest testing, only the transformer and coax have remained unchanged.

    Overnight we got a couple of inches of rain, so I though things might change. They didn't. The complex impedance measurements were the same at noon today as they were at about 7:00 PM last night.

    If you have downloaded the PDF link above, my transformer is exactly as shown, on a T106-2 core. It is a very simple tri-filar winding on a T106-2 core, resulting in a 9:1 voltage un-un. I've settled on exactly 50 feet of 50 Ohm RG-58/U as the feedline, as it is easy to make, buy, and use. I tried a number of other coax lengths, and I've tried various lengths of 75 Ohm RG-59/U. I chose what I did because it worked consistently across 80-10 meters.

    The antenna radiating element and the radials are #20 teflon coated stranded electrical wire. The feedpoint/transformer is about 12-inches above ground. The radials are laying on top of the ground. I've measured complex impedance at the "shack end" of the coax with radiating elements ranging from about 20 feet to about 60 feet in length, and with various numbers and various radial lengths.

    With the end of the 42 feet and 9-inches of radiating element, up at about 38 feet above ground, and with the feed point/transformer at about 12 inches above ground, I saw extremes on 80 through 15 meters of:

    3.75 MHz, I measure Z = 76 + j1 (SWR about 1.5:1)
    14.175 MHz, I measure Z = 37 - j2 ( SWR about 1.4:1)

    Ten meters was not quite as good using a 42-foot 9-inch length of wire and 15 foot radials. But, it was quite acceptable for a portable antenna. At

    28.5 MHz, I measure Z = 51 + j18 (SWR about 1.4:1)
    29.0 MHz, I measure Z = 77 + j9 (SWR about 1.6:1)
    29.5 MHz, I measure Z = 102 - j10 (SWR about 2.1:1)

    Each band was measured across the US non-WARC frequency extremes on 80/75, 40. 20. 15, and 10 meters.

    I was surprised when I was first testing these antennas early last week. Ten and 15 meters were both open to Europe and Scandinavia from here in the mountains of West Virginia on the vertical antennas. Using my little Ten Tec Argonaut 505 at about 3 watts SSB PEP, I made a number of contacts on both 10 and 15. I couldn't even hear these signals on my 137 foot doublet. I am presently writing that off to propagation variations.

    Enough for now. But, this may be food for thought. According to all the the initial writings I could find about these antennas, they should require antenna tuners to provide a reasonable 50 Ohm match to a transceiver. By doing the optimizations I did, I am not using them with a tuner. For comparison purposes, I am using my 137 foot ladder-line fed doublet antenna through an optimized coaxial choke per-band, and a properly tuned L-Network to provide a 50 Ohm impedance to my transceivers. I've also been using a single coil Z-matching link-coupled balanced tuner with the 137 foot doublet. Other than the Z-network being a lot narrower in bandwidth, I cannot tell a difference between the two tuners when used with the doublet.

    The weather is beautiful here in the West Virginia mountains. I'm going fishing.
    KK4NSF and W4SEX like this.
  2. KI6J

    KI6J Ham Member QRZ Page

    "Whoso pulleth out this sword of this stone is rightwise king born of all England".
  3. W7CJD

    W7CJD Ham Member QRZ Page

    1. efficient antenna

    2. effectively deployed

    3. specifically for low power QRP, either portable or QTH

    4. explain how-to, preferably without "cut-and-try" method

    5. demonstrate "step-wise" using an antenna analyser or VNA and/or antenna modelling

    ..any example?

    not even one?
  4. AI6KX

    AI6KX Ham Member QRZ Page

    Shortly after crying about how it's so hard to find antenna materials on the Moxon thread, I found a fantastic range of fiberglass telescoping rod blanks at a general-goods store in my wife's hometown. They are (natch) Chinese made, and come in light and heavy grades, lengths 2.7, 3.6, 4.5, and 5.4 meters. I bought one of the 5.4 meter heavies (still weighs less than a pound) for about $14 and 2 of the 2.7 meter heavies for $5 each. (The lightweight ones were only a little bit cheaper).

    I've seen one use of a light telescoping pole as a 40-meter vertical. Can anyone steer me to similar ones? I am only interested in 20, 17, and 15 for portable work, but quick bandchanging is important to me, which is why I rely on a fan dipole. (I also am experimenting with a 41' wire and a T-match tuner.) But for the beach a vertical makes most sense, which is why those rods jumped into the shopping basket. Maybe something like loops at different lengths on the rod so I can fold bare wire down to shorten for the higher bands? And something like kite reels for the radials? I am hoping that only 1 or 2 radials is enough at the beach or if they are on the ground. I would also hope to feed with coax but can use a tuner as well. Or feed a fixed height (16') vertical and radials with open-wire line and use the tuner?

    What think the seasoned QRP'ers?.

    Steve in Okinawa JS6TMW
    W4SEX and KC8VWM like this.
  5. W7CJD

    W7CJD Ham Member QRZ Page

    He doesn't recommend having radials or counterpoise on the ground, at the beach.
    W4SEX and AI6KX like this.
  6. W7CJD

    W7CJD Ham Member QRZ Page

    ..strictly QRP

    Waters Edge HF Pedestrian Mobile

    He has three video, at YouTube.

    The other two Waters Edge HF Pedestrian Mobile video have less surf.

    Here is his "ground tuning unit".
  7. AI6KX

    AI6KX Ham Member QRZ Page

    As a followup, I found that a 41-foot wire works fine on 20, 17, and 15 with my cheapie T-match tuner, fed with 10 feet of coax. It's a "sweet spot" for an end-fed wire and a good length to toss up into a tree. Today I forgot to bring the DMM to measure RF output voltage but actually had no trouble tuning by the LEDs. Good DX on the high bands today...

    Steve JS6TMW in Okinawa
  8. KD8EDC

    KD8EDC Ham Member QRZ Page

    This is a FANTASTIC idea. I'm going to go ahead and build one, and probably use it with a 31' Jackite pole. What is the gage of the flexweave wire that you used? I looked around for reels; most contain 21' of line. For a 40m 1/2 wave dipole, one would need to put about 33' on the reel if the desired center freq was about 7.100MHz or so. I'm only able to find FlexWeave (Davis RF) sold at #12 or #14 gage; seems pretty thick for the reel. Someone did note that they got 33' on one of these reels, but they used #22 wire. Looks like you used bare wire, which would make sense.

    Thanks for the help!!!

    BTW, here are the reels I found:

    Mark KD8EDC
  9. K8JD

    K8JD Ham Member QRZ Page

    One Good QRP antenna
    One pretty effective and simple antenna I tried for portable was a dipole/feedline made of old TV antenna 300 Ohm twinlead.
    If you are reading this you probably are not of the recent generations that don't remember roof mounted Over-the-air TV antennas. They were nearly always fed with 300 Ohm TwinLead wire, !
    I used the twinlead to make a folded dipole and also for the feedline.
    This antenna was cut for 30M and needed a transformation to 50 Ohms for the MFJ 9030 I was using. I had a small MFJ 16010 tuner that had the built-in 4:1 transformer. It was simple to tune using a small RadioShack SWR meter.
    All this was light weight and the antenna/feedline was wrapped up on a cardboard square for transport. I taped some light cord to the ends of the twinlead dipole to hang it up over tree branches.
    The Idea of using 300 Ohm twinlead was The Z or the folded dipole and feedline matched up well, would make a low SWR system that the tuner/4:1 BalUn transformer was also a good match for. The theory of this antenna is well documented.
    Finally, The weight of the twinlead was less than the Coax fed dipoles and easy to deploy, then wrap up to transport to and from sites..
    The on-air results on 30M with QRP were very favorable with this antenna.
    Last edited: Feb 8, 2016
  10. W7CJD

    W7CJD Ham Member QRZ Page

    That tv twinlead would just about spring into action, released from how it was rolled up and secured.

    Do you have a link for the twinlead folded dipole?

    It is only measure and cut for band, then how much length, then, for the feedline?

    It is a balanced feedline to the tuner?

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