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2 meter vertical feed connection

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KL3PW, Oct 12, 2017.

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  1. KL3PW

    KL3PW Ham Member QRZ Page

    Hi, I am making a 2 meter vertical that will stand up to the weather here in Alaska. I have tried using the UHF mount design but the element always flexes after time that it breaks so i opted to make a more robust one. I am using 6ga solid copper ground wire for the element and 4 gauge copper for the ground planes ( 4 x at a 45*). I have threaded the element and secured it in a chunk of plastic cutting board so it can be isolated from the angle aluminium. The ground plane radials are not a problem but was wondering about the feed line from the connector. I have included a pic of the connector and link to the element. My question is, with the link being this close to the ground portion ok, or should I shield it in some way? It will be on top of a 25 foot mast on the peek of the roof ( 2 story ) so i hope this is the last time i need to drop and raise it for some time. Any input would be most appreciated.
    Thank you,
    Andy
    KL3PW
     

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  2. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    Assuming nothing moves at all, you have enough spacing there to handle a kilowatt at 50 Ohms.

    Remember the connection from the SO-239 center pin to the copper radiating element itself all adds to radiator length and is all part of the antenna (looks like 1/2" to 1" or something), so the radiating element will need to be shorter than formula length to resonate where you want it to on 2 meters.

    I don't like any gauge copper wire for this (even hard-drawn #6) as copper is soft and heavy compared with extruded aluminum tubing which is very hard and lightweight (which is why antennas are almost all aluminum tubing).

    Also, if you get wind or precipitation static there, or any nearby lightning, a folded monopole which is at DC ground potential is both mechanically stronger and also a better design as it shorts out static and lightning charges to ground; this is a more common design in commercial VHF ground planes you'll see at airports and most government installations and it makes sense.

    But with respect to the air gap shown between the center conductor and ground...should be fine, it's as much as the connector itself has.
     
    NH7RO and WA7PRC like this.
  3. WA7ARK

    WA7ARK Ham Member QRZ Page

    How about using a 1/4 WL stainless steel whip on an NMO mobile mount. I have one on my airplane, and it has stood up to 165mph "winds", including "gusts" (buffeting because it is in the turbulent flow caused by the prop) for years...

    I would use stainless steel rods for the ground-plane elements, too.
     
    Last edited: Oct 12, 2017
  4. KL3PW

    KL3PW Ham Member QRZ Page

    Thank you for the input. Regarding the length, any feed line, connections, joints, anything added to it after the shielding is considered part of the main element, horizontal or vertical and tis length is counted when calculating the overall size of the antenna. Correct?
     
  5. KL3PW

    KL3PW Ham Member QRZ Page

    As for the whip idea, i would use a mno , non loaded coil base with the same 4 ground plane elements?
     
  6. WA7ARK

    WA7ARK Ham Member QRZ Page

    Here is a world of possibilities using NMO mounts. You might prefer to put a 5/8 wl "gain" antenna on the mount instead of 1/4wl simple whip.

    Stainless steel rods of about the same diameter as the standard whip are available at a RC modelers store.

    You can even get a kit
     
  7. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    Yes, that's true.
     

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