Mobile Antenna for HF USE

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by 9H5JY, Feb 26, 2021.

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  1. 9H5JY

    9H5JY Ham Member QRZ Page

    Hi

    is their someone has dimensions for a mobile homebrew antenna for HF 20M and 17 M

    I needed for car mobile use

    Regards
    9H5JY
     
  2. AK5B

    AK5B Ham Member QRZ Page

    Seems like very few hams home-brew mobile antennas any more. Of course, there will always be exceptions but the majority use either something like a cheap hamstick or an expensive but more efficient screwdriver design that is remotely tunable.

    One way to at least partially home-brew one would be to make a 54-inch mast akin to a Hustler MO-4 Mobile Mast with copper plumbing pipe, copper fittings and some 3/8th by 24 thread bolts/couplings, then attach a Hustler RM17 or RM20 resonator to the top. A home-brew capacity hat could also be added for more efficiency as well as reducing ground loss (it gets the current node higher away from lossy ground). This would result in a center and top-loaded shortened vertical; one of the best types to aim for. The "mast" is actually the bottom section of the radiating element as it puts the coil in the middle, more or less---better than a base-loaded radiator by far.

    Such a "hybrid" home-brew/commercial mobile antenna could almost perform as well as an expensive screwdriver if used while parked close to your many beautiful Mediterranean shores of Gozo---vertical antennas gain 6db of low-angle propagation enhancement when over or closely adjacent to saltwater.

    If you need details on constructing the mast part I can round up a link for you. The only problem with that is that I doubt you would have SAE (American) plumbing pipe and bolt thread sizes available in Gozo, right?

    Let me know if I can be of further help and good luck going HF mobile around your island, Jeff!

    73,

    Texas Jeff
     
  3. KH6AQ

    KH6AQ Ham Member QRZ Page

    9H5JY, it can be built around materials you have on hand or can easily obtain. What have you got to work with?

    Electrically the mobile monopole can be up to 1/4 wavelength on 17 meters, or almost 4 meters. That likely too long for a vehicle so select anything that fits, the longer the better. A base loading coil is fine although a center loading coil offers higher radiation resistance. By the time vehicle GND resistance and loading coil loss is added the radiation efficiency is not much different but the center loaded may offer greater SWR bandwidth. Once you select a length I can model it using EZNEC.

    14.2MHz, 3 meter whip, base loaded, radiation resistance = 10 ohms.
    14.2MHz, 3 meter whip, center-loaded, radiation resistance = 17 ohms
     
    AK5B likes this.

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