Proper Grounding for Homemade Mobile Attenna Mount

Discussion in 'Mobile Radio Systems' started by KB9WBX, Mar 14, 2011.

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  1. KB9WBX

    KB9WBX Ham Member QRZ Page

    Hey All,

    My Title was probably confusing, wasn't sure how to describe what I'm doing in one sentence, so I will go more into detail here.

    I got a new nice mobile antenna that I want to use for one of my Mobile Radios that I run in my house.

    What I was planning on doing was cement into the ground one of the standard #2 Fence Posts, the ones that are 4x4 inch wide. I would put it standard depth in the group so that 8 Feet of Post is above ground (typical depth that would support a heavy fence).

    I was then going to cut a 5x5 inch square of some metal material and screw it into the top of the post.

    I was then thinking I would drill a hole towards the edge of the metal to use to attach my ground wire that would go to a standard grounding rod in the ground.

    So then the mag mount would attach to the metal and I have my mag mount antenna on top.

    So that was my plan, as I really want to use this antenna, and wanted to place it somewhere behind my house, somewhat hidden.

    So I guess I'm looking for some advice/opinion on the following items:

    1. Is this a good idea, it should work?

    2. What type of metal is best to use as my 5x5 inch plane.

    3. Would it be sufficiently grounded by attaching ground wire to the plane, which the antenna mag mounts to?

    4. Any other opinions? We think this should work? I couldn't think of any other solution to build, and figured with antenna on top of 6 foot post it would be about as high up as sitting on a typical suv.

    Appreciate any and all advice!!

  2. M0GVZ

    M0GVZ Ham Member QRZ Page

    DO NOT USE A MAGMOUNT. They don't provide a very good connection. Instead create a plate bent at right angles, screw the vertical bit into the wood and use a 3/8 body mount on the horizontal part.

    The radials will need to be cut at a quarter wave and you'll need 4 of them for each band and they need to be kept clear of the ground. They need to meet as near as possible to the feed point so attach them to the vertical section of the plate or drill holes in the horizontal section to screw into or feed a bolt through.
  3. KB9WBX

    KB9WBX Ham Member QRZ Page

    Oh yeah, I forgot about that type of approach. Putting the antenna onto one of those mounts instead of the mag mount base.

    I thought I saw a kit from AES or HRO for putting Mobile Antenna on a mount like that. Came with the Qtr Waves and such. I been searching the last hour on their catalogs and haven't found anything yet.

    Anyone know of a good kit that will save me some time as apposed to making it? If I make it as noted below or find a kit, would I be properly grounded by just attaching the ground wire anyone I drill a hole on the Plate? Is it just pick a spot and attach the ground wire or some place better than others?

    Thx again for the feedback.
  4. W0HU

    W0HU Ham Member QRZ Page


    You may want to Google the Larsen antenna site, particularly about base station kits. I think you will find some interesting items there that may provide an operable solution for you. I have used these successfully where there was not space for a full-sized base antenna.

  5. KF5FEI

    KF5FEI Ham Member QRZ Page

    I assume we're talking 2m or 70cm. There are various (MFJ, Larsen) types of base station "adapters" for mobile 2m and 70cm antennas available. However, they typically fit the SO-239 or NMO mount antennas, IIRC. In any case, you'll still need a bigger piece of metal to provide an adequate ground plane. You also have an issue with potentially exposing people to RF and / or a shock hazard if you run a at higher power.

    For a stealth antenna that friends have said work very well, the Ventenna seems to be a winner. Guy up the hill has one and it does almost as well as the smaller colinear I have at my house.
  6. K8JD

    K8JD Ham Member QRZ Page

    Is this for HF bands or V/UHF ?
    If U/VHF I would expend my energy getting it up on top of the house rather on the ground ! Line of sight comms work better higher up !:eek:
    For HF, there are lots of radial guidelines discussed in these forums, for your antenna.
  7. KB9WBX

    KB9WBX Ham Member QRZ Page

    Hey All,

    Appreciate all the feedback. It is 2m/70cm...Also it is S0-239 connect as the antenna is the Diamond SG7900.

    From your feedback a am re-analyzing my approach. I deffinately like the idea of the base station type adaptor instead of putting this in a mag mount, thats great advice.

    Also I hear you loud and clear about doing the extra mile to get it on top of the house instead of my land mount idea. I have a chimeny so I could mount it on the backside of the chimney, just need to see what the home depot has for stuff that will drill into a chimney. I assume the base mounts your referring to would probably mount to a Pole, so would need some brackets that can have screws into the brick cement chimney and then attach maybe a 3 foot pole.

    I guess though that brings up a spin on grounding it. As Im not an expert on grounding. So if I do this then the wire that goes to the ground rod would run along the roof and down the side of my house to the ground. It will be touching the house is my point. I assume thats ok that it lay/be attached to the actual house structure as it follows to the ground? Unfortunately my chimney is in the middle of my house, and not at the end of the house were I could of had the wire go directly to the ground without touching the house.

    Only other thing I can think of is a "sat dish" type pole mount and put it on the side of the garage wall so ground wire can go straight down... but then I think antenna would be blocked some by the house. Having on the chimney I think really gives optimal view of the sky.

    Apprecaite the continued help.
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