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Where to fit an Antenna Filter and a Surge Protector / Static Grounding Block ?

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  • Where to fit an Antenna Filter and a Surge Protector / Static Grounding Block ?

    Iím seeking best practice or your thoughts and suggestions on where to place the above items in the coax cable run.

    Firstly, Iím aware that some Active Antennas require grounding and assume this is for some protection against static spikes / voltage surges etc. Iím also aware that most Ďprofessionally installed' radio antenna systems have a voltage surge /static discharge grounding near the point where the coax leaves the tower or mast and a ground wire continuing down to an earthing point.

    So Ė would best practice be to have the 1090MHz filter at the antenna end ? or inline somewhere along the coax run ?? or immediately at the receiver input ??? And the same questions about where to position the surge/static protection.

    Given cable loss factors and limiting the number of connector joins, would a solution be to connect the antenna filter directly to the antenna, then connect the surge/static grounding block to the antenna filter, with the ground wire to earth, leaving an unjoined coax run directly to the receiver? Or does it matter where they go as long as they are installed somewhere ?

    Cheers

    Peter

    ylis

  • #2
    All antennas should be grounded for static/EMP protection. Passive antennas should also be center-DC-grounded (active antennas can not, since they need +VDC on center) and like you say preferably equipped with a discharge protector before entering a building or equipment shelter.

    The question is now what is possible and reasonable for a non-commercial installation. Most domestic TV antennas have never been grounded (other than possibly through the TV) and very few are ever affected by lightning. Most domestic lightning damage is actually coming from the telephone lines, affecting mainly equipment that is connected to both AC and telephone circuits.

    But, it is of course no downside to proper grounding IF you can provide a suitable ground connection, like a rod or buried copper wire. There is no evidence that a grounded antenna in any way "attracts lightning" other than from a very small area above your house. Lightning is quite stochastic in that sense.

    Just connecting to the building's AC ground can help from static buildup, but can cause more widespread damage if a larger discharge is led down to other AC equipment. So it is a matter of personal preference/risk assessment if that is the only available ground. Also check local electrical code, it may very well be forbidden.

    The placement of the filter does not matter since you have no LNA inline, so put it just before the Rx as it is best protected and easiest access.

    /M (25 years in telecom)
    F-ESDF1, F-ESGG1, F-ESGP1, F-ESNK1, F-ESNV2, F-ESNV3 F-ESSL4, F-LFMN3
    P-ESGR, P-ESIA, P-ESIB, P-ESGF
    mrmac (a) fastest.cc

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    • #3
      1) for the surge protector - From what i have seen others do where the cable enters the property seems popular (probably for mounting/earth access convenience), in theory the device breaks down when there is an excessive surge on the inner core and dumps it to the screen of the coax. So it shoudn't matter where it goes however a location with the shortest path to ground would makes sense. For my installation i have a dedicated earth spike at the mast base (mast earth) and i run a cable from the surge protector to that and not the house earth.

      2) Filter Location - If you not amplifying the signal then i would mount the filter at the receiver. Simply for weather robustness and far easier to try another one if you want to.

      3) Losses - Connecting the filter to the surge protector and then directly to the receiver would in theory save you two connection losses, it all kind of boils down to if you need the marginal gains by putting them together. Using good quality cable and connectors you probably wouldn't be able to notice the difference in having the surge protector somewhere in the middle of your run if that's the shortest path to earth.

      Edit didn't see MrMac's post but it looks like we agree.
      Last edited by SpaxmoidJAm; 2018-01-08, 21:22.
      T-EGLF8

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      • #4
        Thank you both for the replies - clear and understandable information.

        To clarify, if I had a LNA ( which I don't ), the filter would need to go between the receiver and bias-T because <most> filters don't have a DC path ?

        ylis

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        • #5
          yep as you have speculated it really depends on the filter
          T-EGLF8

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          • #6
            Originally posted by ylis View Post
            To clarify, if I had a LNA ( which I don't ), the filter would need to go between the receiver and bias-T because <most> filters don't have a DC path ?
            Depending on how strong interference you have, the filter MAY need to go between the antenna and LNA. Then you also don't have a problem with bias.

            /M
            F-ESDF1, F-ESGG1, F-ESGP1, F-ESNK1, F-ESNV2, F-ESNV3 F-ESSL4, F-LFMN3
            P-ESGR, P-ESIA, P-ESIB, P-ESGF
            mrmac (a) fastest.cc

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