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First Antenna at Home - Fan Dipole - Suggestions Wanted

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KK6KC, Nov 6, 2015.

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  1. KK6KC

    KK6KC XML Subscriber QRZ Page

    I am a new Extra, and am about to put up my first antenna at my home. I plan to put up a Fan Dipole, 80, 40, 20, and 10 meters. I don't have a spot to put up a tower.
    Here is my house layout:
    North is up. The white line is where the dipole will be. The red dot is a 30ft mast with a TV antenna on the top. The yellow line is the power feed to my house. I plan to attach the dipole with ropes and pulleys to the trees at either end. The trees on the East end are about 40ft. The west end about 20 ft. The Ham Shack is in the house about where the 100ft mark on the dipole is.

    I plan to use 12 gauge stranded THHN insulated wire from Home Depot. Ill make my own center insulator that spreads the individual dipoles about 6 inches apart at the feed point. I'll use pvc spreaders to keep them in line along the way and at the ends they will be about 4 feet apart.

    I plan to use RG8x for the feed line, and I don't have an antenna tuner.

    Do you guys have any comments or suggestions for this setup?
  2. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Sounds cool.

    But your white line shows a length of 124.62 feet with no dimension shown for the distance between the trees; it looks like it might be enough, but you'll need (as you wrote) insulators and ropes at each end and they will hopefully be several feet long each. Use good end insulators between the ends of the wires and the ropes.

    Also not noted is how high the trees are. Such a parallel dipole will have substantial sag in the center, probably 5-10 feet under calm conditions, and of course you'd want the center to be as high as possible.

    I'd also recommend a good 1:1 current balun at the feedpoint; you can use a balun as the center insulator, and if you do that you probably won't need to build your own center insulator. There's some stuff like this that's commercially made and already on the market:

    One last comment is that 124.62 feet might be a bit short unless you're focusing on only the high end of the 75m phone band. To hit 80 meters, you'd normally need this to be longer.

    Nice project, get it up!
  3. KK6KC

    KK6KC XML Subscriber QRZ Page

    The 124.62 feet number is just what the tool on Google Maps gave me. It is hard to get it to an exact number. The longest dipole will be set for 80 meters. The front tree is about 40ft high and the rear 20 feet, so it will slope a bit towards the west.
  4. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    With one end at 20 feet, the center of the antenna might be nearly on your roof due to 'sag' unless you tension the supports a lot. Maybe 100 lbs or a bit more would take half the sag out of it, but it will always have some.

    Would it be possible to install a 40' mast against the trunk of the 20' tree (strapping it to the tree) to get that end up higher? If possible, that will certainly work better.

    Also, where are you? Your address shows Lomita, which is in L.A. county near the airport but the grid square information provided is up east of San Jose.:)

    If you're in Lomita, you're surrounded by lots and lots of knowledgeable hams who might provide assistance. I'm about 25 miles from you, but others are much closer.
  5. KK6KC

    KK6KC XML Subscriber QRZ Page

    My map location was where I was on a recent business trip. Now it is updated. I live in Lomita. That mast idea is a good one. It would certainly help the West end. I plan to put up a test rope when i have a chance to see what height things really are.
  6. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Cool. Do you know Chip, N6CA? He's pretty close to you...
  7. KK6KC

    KK6KC XML Subscriber QRZ Page

    Sorry, I don't know Chip.
  8. AK5B

    AK5B Ham Member QRZ Page

    Don't know if it's really doable but I'd try to utilize that 30 foot mast atop your roof to run a support rope to the balun/center insulator---if you had something across (North of) from it maybe that could happen---otherwise no big deal. I'm assuming that your TV antenna sits around 42-45 feet above ground, correct? A thin Dacron rope tossed over it with a small weight might be the way to do that if you think it would be worth the trouble. Forgive me if my suggestion appears ridiculous; it is just a thought that came to my mind at first.

    Anything you can do to get the whole thing higher will benefit you when it comes to chasing DX, of course. Have fun and enjoy your full privileges, too.

    73, Jeff
  9. WA7DU

    WA7DU Ham Member QRZ Page

    Welcome to the radio hobby. Based on the posts above, you have been well-advised with uncommon expertise. Two tidbits from a radio commoner...

    1) The ends of dipoles are high voltage points. Be careful that they don't contact flammable material where an arc could ignite something.

    2) You will need (by virtue of the National Electric Code) lightning/static charge build-up devices at the point the feed-lines from your antennas enter the house. That is accomplished with a surge arrestor or a coax cable shield grounding device and a co-located driven ground rod. That ground rod must be bonded to the AC utility ground bus at the main distribution panel. A proper surge arrestor will protect both elements of your dipoles; if you choose the alternative shield grounding method, you will need to add an RF choke or a resistor from coax center conductor to ground.

    At this point, you are probably thinking that lightning is such a rare event in your area that this cannot be a high priority. However, static charge build-up is a hazard to your radio equipment without any lightning at all. Wind-blown dust or just rain can create static charge build-up. Santa Ana winds...well, 'nuff said.

    Enjoy the hobby. 73
  10. KH2G

    KH2G Ham Member QRZ Page

    Building tip - after you cut your wire, put one end in a vise and pull the wire firmly to stretch it out before hanging it as copper wire does stretch and you will see it sag over time. This is why my wire of choice is copper clad steel. I know it is more work but it eliminates the stretch factor. The price may be a bit better than pure copper but I have not priced it in awhile but was that a 500 ft spool was fairly cheap and last a long time. If you do work with copperclad, be sure to wear safety goggles as it is very springy! Enjoy 73 Dick KH2G
    KB0TT likes this.

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