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Thread: UHF losses in long bulkhead connectors

  1. #1

    Join Date
    Aug 2019
    Sequim, WA

    Default UHF losses in long bulkhead connectors

    I need to pass lmr400 into my house through a 7" wall. 1" Siding, 5 1/2' insulation, and 5/8'' wallboard. I do not want to bend the coax, so a right angle connector to a plate
    on the outside of the siding. I have seen 8'' bulkhead passthroughs, female N on both ends, but have read they are to be avoided like the plague on vhf/uhf. The radio is
    only 6' from the inside wall. I really would like to keep the losses as low as possible, the antenna is 100' away. Antenna is a Comet gp9, up 40'. I am tempted to just drill
    a small hole through the walls, pass 8' of lmr240, and attach appropriate connectors. I am new to vhf/uhf, and lmr400, but many years of HF experience. The purpose of
    all this is to provide a relay for search teams and the area communications center, and I went through hell with my HOA and city building inspector to get permission for
    the antenna. So, any tips from you will be greatly appreciated. I have only purchased the antenna so far, almost everything is ready to buy, just the connector design
    holding me up.
    73, Dale, K7MPZ

  2. #2
    Super Moderator 5B4AJB's Avatar
    Join Date
    Mar 2008
    Meneou, Cyprus


    An aluminium plate on the outside with a socket on it seems the most practical method for permanent installation with a hole cut into a mains socket blanking plate inside.

    However, more connectors = more losses.

    There are sash window mounting kits, which are simple to make if you have this kind of window.

    Lots of hams simply drill through the window frame.

    If you do make a hole anywhere, drill slightly downwards from the inside to stop water running down the coax and inside.

    You might be able to fit a socketed plate outside and one inside if you can manage to push the excess cable into the wallspace, then you can have them at different heights...

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