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Thread: Antenna Height vs Coax Length

  1. #1

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    Default Antenna Height vs Coax Length

    Hello,

    I'm getting back into amateur radio and I'm looking for an HT/Base station Dual Band Antenna for VHF/UHF. I have several mounting options: roof peak, side of the house, or stand along pole next to the house.

    The height of these options goes from tallest to shortest, the length of the coax run goes longest to shortest in conjunction. So which is more important, height of the antenna or shortest run of coax?

    I'm guesstimating that the highest mount would result in a coax run over 50'.

    I have been looking at Diamond X50A or equivalents (Tram/Comet) or a DBj-2 Dipole. Any suggestions or advice would be most appreciated.

    Thanks,
    Lou

  2. #2
    Super Moderator 5B4AJB's Avatar
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    Default

    Antenna height.

    If you're serious about mounting an antenna up high for VHF, you will need good coax. Avoid RG213 for runs over about 20-30 feet, it just isn't good enough for VHF.
    Whilst you have a decent antenna height, you may as well put something with a bit more gain than an X50, I have seen the difference between an X50 and an X200 on the same coax run, ignoring the price difference, the performance is well worth it.

    An X50 with RG213 mounted a few feet higher than the chimney stack does work well, but the difference with good (better) coax is quite surprising. Swap the X50 for something a bit better still and the difference is even greater.

    In short, feeder is more important than the antenna at VHF/UHF, more signal from the antenna will reach your transceiver and vice-versa. The coax & antenna may cost more, but you will make more contacts...

  3. #3

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    What you need is an Elmer. Buy a decent 50w mobile and some LMR 400 or Belden 9913 and the biggest antenna you can find.
    Diamond X510 or Browning equivalent would be my choice.
    I don't do walkietalkies or j-poles. But if all you want to do is talk locally, to the local repeater, your best choice is probably a j-pole mounted on 10' of pipe beside your backporch with some RG8x and a N connector adapted to what ever antenna connector is on the squawk box. Pl connectors has an impedance bump. Squawkboxes are not designed to run external antennas.
    When the SWR increases - which a rubber duck has no swr since it has no feed line, the rig tends to fold back its power, negating any real gains the height gain of the antenna makes. A cheap 5w Chinese radio probably radiates 1 watt into my Diamond antenna with 60' of coax. On a mobile, my old Radioshack HTX 202 works decent with a MFJ walkie talkie mobile antenna stuck on the roof, fed with cheap coax and a factory bnc connector, so long as I am on top of a mountain when I try to talk.

  4. #4

    Join Date
    Apr 2020
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    Crossille, TN
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    Default

    Thanks for the reply. I'll look into a higher gain antenna and keep the coax length a short as possible while using the best quality I can afford.

    Regards,
    Lou

    Quote Originally Posted by 5B4AJB View Post
    Antenna height.

    If you're serious about mounting an antenna up high for VHF, you will need good coax. Avoid RG213 for runs over about 20-30 feet, it just isn't good enough for VHF.
    Whilst you have a decent antenna height, you may as well put something with a bit more gain than an X50, I have seen the difference between an X50 and an X200 on the same coax run, ignoring the price difference, the performance is well worth it.

    An X50 with RG213 mounted a few feet higher than the chimney stack does work well, but the difference with good (better) coax is quite surprising. Swap the X50 for something a bit better still and the difference is even greater.

    In short, feeder is more important than the antenna at VHF/UHF, more signal from the antenna will reach your transceiver and vice-versa. The coax & antenna may cost more, but you will make more contacts...

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