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Calculating Antenna Length on an Inverted L

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by W3KDK, Jul 7, 2016.

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  1. W1VT

    W1VT Ham Member QRZ Page

    While convenient, installing a random wire under the eves isn't a good place to put it from a performance standpoint. It is likely to be close to household electrical and electronic devices that generate noise. If you can do it, it may be quieter to put a remote antenna tuner at the base of a tree and run the wire up the tree, then back to the house.
     
  2. WD0BCT

    WD0BCT Premium Subscriber QRZ Page

    I should have mentioned that a stealth installation was required and all trees were on common green belt property. Later discussion with our HOA revealed that a small wire into the trees would be OK, however, the tall type of tree (Blue Spruce) would have made a reliable anchor point in the tree difficult. An undereave inverted vee sloped down to a pair of bird feeder stanchions works nicely.
     
  3. W1VT

    W1VT Ham Member QRZ Page

    If you have no trees, an option may be a flagpole supporting the American Flag. President Bush and his brother signed laws for the USA and Florida. The former covers the entire country. The one for Florida is pretty specific on what can be put up. My QRZ home page shows a 20' flagpole as an example.
     
  4. WA7ARK

    WA7ARK Ham Member QRZ Page

    The problem is that the antenna is not just the wire that the hot terminal of the remote tuner is connected to; the optimum length of the wire is strongly dependent on what the ground terminal of the tuner is connected to as well.

    Same is true if the end-fed antenna is the step-up transformer-fed non-resonant kind, or the resonant kind that is fed via a 1:49 transformer

    If the tuner ground is connected to radials, it depends on the radial length, number, layout. It depends if there are radials for the particular band or not (e.g. if all you have are 80m radials, they aren't effective on 40m).

    If there are no radials connected to the tuner, and you are relying on the feed coax shield to act as the "counterpoise", then the optimum wire length will yet be different. Connecting the tuner ground terminal to a ground rod will yield still different optimum lengths.

    In other words, the problem is so complex that you have to use an antenna modeler with an optimizer to find the actual best lengths (or at least to avoid the ones that are impossible for the tuner to drive).
     
    Last edited: Mar 17, 2019
  5. WD0BCT

    WD0BCT Premium Subscriber QRZ Page

    You don't need a flagpole to display the flag...a flag pole can be banned.
    A residence mounted flag staff of 5' or shorter meets the flag display requirement as most HOA's will smilingly report. But don't even think about placing it upon the roof!
     
  6. W1VT

    W1VT Ham Member QRZ Page

    http://www.leg.state.fl.us/Statutes...ute&URL=0700-0799/0720/Sections/0720.304.html This is what the law in Florida says
    (b) Any homeowner may erect a freestanding flagpole no more than 20 feet high on any portion of the homeowner’s real property, regardless of any covenants, restrictions, bylaws, rules, or requirements of the association, if the flagpole does not obstruct sightlines at intersections and is not erected within or upon an easement. The homeowner may further display in a respectful manner from that flagpole, regardless of any covenants, restrictions, bylaws, rules, or requirements of the association, one official United States flag, not larger than 41/2 feet by 6 feet, and may additionally display one official flag of the State of Florida or the United States Army, Navy, Air Force, Marines, or Coast Guard, or a POW-MIA flag. Such additional flag must be equal in size to or smaller than the United States flag. The flagpole and display are subject to all building codes, zoning setbacks, and other applicable governmental regulations, including, but not limited to, noise and lighting ordinances in the county or municipality in which the flagpole is erected and all setback and locational criteria contained in the governing documents.
     
  7. WD0BCT

    WD0BCT Premium Subscriber QRZ Page

    In Colorado:

    ● HOAs cannot prohibit the installation of flagpoles. However, associations are permitted to regulate the location and size of flags and flagpoles.
     
  8. KL7AJ

    KL7AJ Premium Subscriber QRZ Page

    Total length should be about 1/4 wave....you'll usually have to do some twiddling with the reactance at the feed point.
     
  9. W5LZ

    W5LZ Ham Member QRZ Page

    The total length is typically from the furthest tips to the center insulator. It honestly isn't that critical depending on frequency of use. At 160 meters adjust lengths by feet. At UHF adjust by fraction of an inch. See where that's going?
    If you fold wire back onto it's self it effectively disappears at RF. So the wire wrapped to secure the insulator isn't counted. You could cut it off. The problem with cutting it off is that if you wanted to make it a bit longer, ain't nothing left to do it with...
     
  10. W2NER

    W2NER Premium Subscriber QRZ Page

    I know this post is a bit old however, thought I would post my setup. I have a 40ft flagpole with about a 120ft long wire off the top (inverted L). This also has a 4:1 nun at the base and I can tune any band from 160-6. I also live in a HOA and I run legal limit with no issues at all. My tuner is a MFJ-998 with has been great, works fantastic and I have had many tuners!!

    [​IMG]
     
    N0TZU, AK5B, WA7ARK and 1 other person like this.

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