Trunk Lid Mount vs. Roof Mount

Discussion in 'VHF/UHF - 50Mhz and Beyond' started by KX4QP, Apr 27, 2019.

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  1. KX4QP

    KX4QP Ham Member QRZ Page

    I'm planning to get a 2m mobile for my car -- considering a Yaesu FTM-3100R (non-removable faceplate, under $150, 5/30/65W, CHIRP compatible -- did I mention I have a limited budget?). Obviously, I'll need to mount a vertical antenna. I drive a 2015 Fiesta sedan, so have choices of fender mount (not preferred), trunk lid (edge mount or through hole), or roof mount. A mag mount that would let me toss the antenna in the trunk wouldn't be a bad thing, but I understand those are less preferred from an operating standpoint as well as prone to damage the paint.

    This will be a permanent mount; I expect to drive this car for another three or four years at a minimum (to around 200,000 miles at least), but if it's through-hole, I'll have to pay someone to install the antenna, as I lack the tools (and skills) to remove and replace the headliner for a roof mount or drill a large hole in the roof or trunk lid (and make it not leak).

    So, first question: is there a significant performance difference between a trunk lid edge mount and a trunk lid through-hole? Ground plane is asymmetrical in the edge mount case, which I understand may lead to a directional radiation pattern. Also, the antenna will be partly shadowed by the roof and pillars, which will have its own effect on radation pattern.

    If the through-hole is a lot better than edge mount, then the question is whether the roof is enough better to accept the significantly higher installation cost, possibility of permanent headliner damage, and increased likelihood of having to replace the whip itself every so often (I don't drive under low clearance often, but that just makes it more likely I'll forget I have an extra meter of antenna on top of the car).
     
  2. OH8GAD

    OH8GAD Ham Member QRZ Page

    Even though, technically, mounting the aerial in the middle of the ground plane is better than at the edge, I doubt you will notice any real difference in performance. In my opinion, I would go for a magmount where you can place the aerial in the centre of the roof, or a clamp-on at the side or boot/trunk lid. That way, there is no need to damage the vehicle.
     
  3. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    In most vehicles having a horizontal or nearly horizontal trunk lid, popping a hole in the center of it for an NMO mount is usually very easy and takes like 15 seconds, and many have no insulation or anything else in the way. Some fancy cars do have some insulation there, but heck -- it's inside the "trunk" and if you make it less cosmetically perfect, this should be a kind of "who cares?"

    The only thing to watch out for, obviously, are braces that are welded inside and will make it impossible to mount the antenna in some areas; so just avoid those.

    There is no special "water sealing" or anything to be done with a standard NMO mount -- it seals itself very tightly against the sheet metal when you tighten the mount as directed, and has a gasket which seals out water, dust, and everything. I've never in my life seen one of these "leak" unless the installer was blind and used the wrong drill or punch size. The correct size (typically 3/4") is such a snug fit to the mount that once it's tightened down it's an airtight seal.

    Only drawback is this puts the antenna a couple feet farther away, so you may need more coax; but many NMO mounts come with 17' of coax preattached, and that's enough for almost any kind of car.

    The trunk edge "lip" mounts can work okay but use setscrews to punch through the paint and make electrical contact with the sheet metal while binding the mount to the lip. I don't really like those, and they not only electrically offset the antenna but they make it easier to grab for kids just walking by the car. The more difficult you make it for that to happen, the longer the antenna lasts if you park the car outside much.

    With respect to damaging the whip: Use an NMO mount whip and NMO mount through the metal, and the whip can be unscrewed and stored in about fifteen seconds, any time you wish to remove it. I unscrew NMO whips hundreds of times (carwashes, or whatever) -- doesn't hurt anything.

    Roof mounting is always best and is more work; I don't like dealing with headliners, either, and usually go to the local Auto Upholstery shop to have them re-install the liner professionally after I install a rooftop mount. They have all the tools and I see they use heat guns in the process, and know what they're doing. It would take me four hours to do what they do in 15-20 minutes. I buy them donuts and coffee.:p
     
  4. AI3V

    AI3V Ham Member QRZ Page

    You have a Ford Fiesta.

    You plan on driving this car until it has 200,000 miles on it.

    And your worrying about paint damage?

    Middle of the roof.

    nmo is a pain to install, because you need a special hole. Magnet mount tends to be rough on coax where the door pinches it.

    Rege
     
  5. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Mag mounts also invite tampering because they're so obviously temporary. Depends where you live and park.

    NMO doesn't need a special hole, the standard one needs a 3/4" hole. I have a 3/4" chassis punch. I drill a 1/2" pilot and use the punch to make a perfectly clean 3/4" hole, and the process takes about a minute. The PITA is the headliner, in most vehicles.

    In my van, the headliner isn't just stretched and clamped, it's also glued using an adhesive. I imagine that's not unusual. Pulling it down is pretty easy, putting it back in place isn't. That's why I hire the pros to put it back, but they can do it during a coffee break.
     
  6. KX4QP

    KX4QP Ham Member QRZ Page

    Yes, I drive a Fiesta, and plan to drive it to 200,000 miles -- maybe longer if it's still in good shape then (my 1990 Aerostar had 240,000 on it when I parked it, but it had a head gasket/mill flat job done by folks who weren't very careful and started leaking coolant again -- and I never drove the kind of commute I have now). I've had the Fiesta almost four years, and it's just about to turn over 90,000. I drive forty-ish miles each way to work, five days a week, so the car is still in pretty good shape, even though I'm nearing the end of the second set of tires, and I still get 40-41 mpg when I don't have to run the air conditioning, even on E-15.

    Another potential wild card here -- I just noticed yesterday that the stock antenna (AM/FM radio and possibly cell extender, roundly ten inches long with an obviously spiral wound radiator) is screwed into its connector in the fairing; looks like an M8 fine thread. That antenna is, accounting for the wrapped radiator, close to the size of the Nagoya 771 I have on my BaoFeng. Would it be practical in any way to use the cable that feeds that antenna with an A/B switch (to preserve stereo function when not using the 2m) and replace the whip with a better matched one?

    Oh, also, "middle of the roof" would have to be offset forward or back, there's a bar of some kind that runs between the tops of the door pillars (presumably rollover protection).
     
  7. W7CJD

    W7CJD Ham Member QRZ Page

    The metal vehicle roof makes a good ground plane.

    I managed to drill the NMO hole in the roof and thread a wire down the back near the door to the floor. I pulled the cable thru. The Pl-259 was added.

    I routed it behind the seat, with the transceiver under the seat. I put the detachable face on the dash.

    There are fold down 2-meter 440-meter antennas. I simply remove the antenna I like and put it in a sleeve behind the seat.

    The NMO has a waterproof cover sold for it, for when the antenna is not in place.

    There is a trick to getting the NMO mount to ground: scrape or emery cloth or both inside and under the hole. The NMO needs to get a ground on the inside and outside of the hole.

    If I use the mag mount, I run the cable thru the passenger side wing window.

    No wing window? I the slightly opened passenger side rear window.
     
    Last edited: Apr 29, 2019
  8. AI3V

    AI3V Ham Member QRZ Page

    Well Steve, I have also installed many, many nmo mounts.

    Not every body has the right. Tool for what is a one time deal for most people, and your claim of a minute is laughable, it's a project to remove the trim and headliner on a modern car, and route the coax around the many airbags.

    Course you have a shop that works for a dollar donut......:rolleyes:

    Rege
     
  9. N8EKT

    N8EKT Ham Member QRZ Page

    Always opt for the NMO mount in the middle of the roof.
    Best performance, most durable, and most immune from tampering.
     

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