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NPOTA activation fri with K2 and random wire

Discussion in 'QRP Corner' started by K4YND, Jan 14, 2016.

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  1. K4YND

    K4YND Ham Member QRZ Page

    Im going to try and activate a NPOTA fri and will be using my Elecraft K2. For 20 meters I have a end fed PARZ. For 40 my end fed died. I am going to use a random wire off the back of the K2. I cant remember the best lengths for the main leg and the counterpoise. Any else done this with a K2
     
  2. KK4NSF

    KK4NSF Ham Member QRZ Page

    I know SOTA and BOTA.... but what's a NPOTA? North Pole on the Air?
     
  3. W7CJD

    W7CJD Ham Member QRZ Page

    National Parks On The Air

    ARRL is the sponsor.
     
  4. W7CJD

    W7CJD Ham Member QRZ Page

    What is PARZ?

    How did the end fed PARZ die?
     
  5. KK4NSF

    KK4NSF Ham Member QRZ Page

    oh..... yeah... I knew that. ;)

    I've not used an end-fed with a K2, but I have used an end-fed with a MFJ9260. I found that I needed a tuner to make it match up right.
     
  6. W4KJG

    W4KJG Subscriber QRZ Page

    People are probably tired of me bring this subject up. It is about a very inexpensive coaxial end-fed wire antenna with its own usable counterpoise (maybe not great, but...). I have tested it with additional counterpoise wires laid on top of the ground.

    Mine is built virtually identical to the original plans published by the Emergency Amateur Radio Club of Hawaii (EARCHI.ORG). http://www.earchi.org/92011endfedfiles/Endfed6_40.pdf

    For this location and installation, I have tested a number of different wire lengths (20, 21, 25, 30, 36, 40, 41, 42, and 50 feet), different coaxial lengths (25, 40, 50, and 60 feet) and different coaxial impedances (50 feet of RG-58/U vs RG-59/U with each of the wire lengths. I have tested with no additional counterpoise, with four 16-foot radials laid on top of the ground at right angles to each other, and with four additional 8-foot radials spaced halfway between the 16 foot radials. (I apologize for not citing the sources of the rather thorough effects of the "diminishing returns" when it comes to length and quantity of radials for similar antennas.)

    I'm still not settled on any final configurations (see next paragraph), but these values seem to work quite well on 80 through 10 meters at this location. Hopefully, in the next couple of weeks I'll be able to do testing with the counterpoise by at least 12 inches above ground. I also want to elevate the feedpoint/balun to 8-12 feet, and test without radials, with the four 16-foot radials, and with the four 8 foot radials. I may add some 4-foot radials also. I plan to test them at various angles between the feedpoint and earth.

    [You might be asking why I didn't model this. Every place I plan to use these antennae will be subjected to very different conditions, especially related to ground loss, which I can't measure. They will range from saltwater saturated ocean sand beach (pseudo-BOTA), to my mountainous farm (pseudo SOTA). Most importantly, I'm doing as much antenna testing here on the farm as possible in preparation for our eventual sale of the farm in about the next two years. After that, I'll primarily be operating from two HOA controlled properties, and I will need usable stealth antennas.]

    The following data was measured with 41 feet of #20 stranded TFTE covered electrical wire, fed with 50 feet of RG-58/U. This particular set of data includes four 16 foot radials at 90 degrees to each other, and laid on top of the earth. It seems to give me the best overall complex impedance results, but maybe I'm just measuring and it is difficult to measure the difference in on-the-air testing/comparing with multiple WEBSDR stations using about 1 watt. My reference antenna is a 135 foot doublet up 35-40 feet.

    3.75 MHz Impedance = 35 - j5 (VSWR =1.5:1)
    7.150 MHz Impedance = 45 + j8 (VSWR = 1.2:1)
    14.175 MHz Impedance = 55 + j0 (VSWR = 1:1:1)
    21.250 MHz Impedance 75 + j8 ((VSWR = 1.5:1)
    28.505 MHz Impedance = 55 + j0 (VSWR = 1.1:1)
    29.000 MHz Impedance = 70 - j4 (VSWR = 1.4:1)
    29. 495 MHz Impedance 65+ j0 (VSWR = 1.3:1)

    It takes enough time to make the measurements that hey are subject to propagation changes while making the changes.

    Results on 80/75 were probably the worst for this antenna compared to my doublet. With the setup above, this antenna was consistently 10-15 dB down below the referenced doublet. Forty and 20 meters were really mixed. There was as much as +/-20 dB of difference between the two. In general though, the end fed was about 3-6 dB down from the doublet. Propagation didn't allow me to make any meaningful measurements on 15 and 10 meters.

    The end-fed wire itself runs at about a 45 degree angle to a pulley connected to a tree. I'd estimate that the open end of the 41 foot wire is about 30 feet off the ground. The top deck railing shown in the photo is about 12 feet above ground.

    [​IMG]

    The 9:1 balun and interconnect box are located about 18 inches above ground. I needed a BNC-to-PL-259 interconnect for the coax. There is about a 6-inch PL-259 to BNC cable connected to the SO-239 on the interconnect box. The counterpoise is connected to the coax shield at the junction of two BNC connectors below the box. I did it this way for easy testing of multiple counterpoise arrangements and cable arrangements. The screw near the bottom right of the box is intended for connecting to the counterpoise when installed for several days, or semi-permanent use.

    [​IMG]

    Lastly, this is how I am connecting the counterpoise for testing. I have a similar setup for the additional four radials.

    [​IMG]

    Anyway, just some of my crazy trials for portable and stealth antennas.

    EDIT: I can't prove it just yet, but this antenna does seem to produce fairly significant common mode current on the coax. Depending on the band of operation, it can wipe out my wireless computer keyboard and mouse, and totally overload my audio system. -- A complete shutdown being necessary to again be operational.

    My 80-20 meter "ugly" balun, located just outside the shack, feeding either my homebrew Z-antenna tuner or my reversible L-antenna tuner resolve the problem.
     
    Last edited: Jan 15, 2016
    RN3ANT and K4YND like this.
  7. K4YND

    K4YND Ham Member QRZ Page

    TR03 (1024x845).jpg Ken, very interesting. Friday I activated the Potomac Heritage trail. It is only 2 miles from my house. I only was able to get on 20 so it took a while to get the 10 contacts. I was at 9 and it took another 50 minutes to get the 10th. In the pic, you can see that the trail is about 30-40 feet from where I was operating. I consider myself a outdoor type and I did not even know this was virtually in my back yard. I think this NPOTA is going to be a blast and will really pick up once it gets warmer.
     
    RN3ANT likes this.
  8. WJ4U

    WJ4U Subscriber QRZ Page

  9. W4KJG

    W4KJG Subscriber QRZ Page

    Hey y'all -- maybe we need a coffee stop or greasy-spoon eye-ball QSO.

    I would have to check, but I believe I could get permission to stage from friends' properties that border nearby national parks that would probably also qualify for SOTA.

    I'm about 15 miles west of Winchester.

    Ken.
     

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