What is the highest gain possible 2-meters mobile antenna that can be used with a magnet mount base

Discussion in 'Mobile Radio Systems' started by KC0BUS, Mar 21, 2018.

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  1. KC0BUS

    KC0BUS Ham Member QRZ Page

    Hi,
    What is the highest gain possible 2-meters mobile vertical antenna that can be used with a magnet mount base on a car roof?
    Thank you
     
  2. K0BG

    K0BG Platinum Subscriber Platinum Subscriber QRZ Page

    Excuse me for being blunt, but you are barking up the wrong tree. In a mobile scenario, gain IS NOT the most important attribute. And mag mounts? are not the answer!
     
    NH7RO, K4AGO and N8EKT like this.
  3. KD2NOM

    KD2NOM XML Subscriber QRZ Page

    For some of us, mag mounts are the only viable solution. For example, I have a leased vehicle and a small budget. I can't be putting holes in the car or my wallet. So my Comet SBB-5 gives me ~5db gain with a mount at the highest point of my car and lowest RF exposure to my occupants and no damage to my paint / body.
     
    K3RW and DO4AMF like this.
  4. W1VT

    W1VT Ham Member QRZ Page

    If you install a roof rack a Yagi and rotator may be possible. I did that to make two EME contacts.
     
    NH7RO likes this.
  5. K0BG

    K0BG Platinum Subscriber Platinum Subscriber QRZ Page

    Maybe you should spend some time on my web site....

    The only time you really need gain, is when working simplex with another mobile station. Even then, high gain antennas have nulls in their patterns with predictable results. When operating through repeaters, high gain antennas are a detriment for the same reason—it is related to the HAAT (height above average terrain) between the mobile and the repeater site.

    I don't know why you drive a lease vehicle, but whatever the reason, a lease agreement DOES NOT prevent you from drilling holes for antennas, especially VHF ones.

    Oh! Zach's answer (beams) may appear factious to you, but the truth is, he just echoed what I said in a different manner.
     
    NH7RO, DO4AMF and K4AGO like this.
  6. KD2NOM

    KD2NOM XML Subscriber QRZ Page

    I think your assumption that all us mobile folks are using repeaters might be the crux of your misunderstanding. I spend most of my time on 2m call frequency during my commute as that is where many of my ham friends congregate.

    And my lease requires me to repair any aftermarket modifications upon lease termination - so you are technically correct - it does not prevent me from drilling holes - it does require me to pay to repair them.
     
    K3RW likes this.
  7. AG6QR

    AG6QR Premium Subscriber QRZ Page

    The answer to the original question is, there is no such thing as the highest possible gain antenna for mobile use with a mag mount. It's always possible to increase gain by adding another phased collinear radiator, or even a director or reflector. But the problem eventually becomes how to aim that gain properly. Especially with mobile operation, it's difficult to know in advance exactly where the other station is going to be relative to your own station. Gain is worse than useless if it's aimed someplace other than toward the station you're trying to reach. For every area of the pattern that has gain, there's another area of the pattern that has loss.
     
    K4AGO likes this.
  8. AF7TS

    AF7TS Ham Member QRZ Page

    Just how complex are you willing to get :) :)

    Mag mounts can do damage to paint, so you may be looking at a false distinction between fixing a hole drilled for a mount versus fixing the paint for a mag mount. Only you know the details of your lease.

    As others have noted, gain comes with the downside of directionality, which can be a pain during mobile operation. If you reduce the signal strength in the direction of interest, your gain isn't helping you.

    From personal experience, I am very happy with a 5/8 wave mag mount, for repeater and simplex operation while mobile. I am planning to upgrade this to a 5/8 wave NMO mount.

    If, for your particular operations, you feel that having more gain toward the horizon would help, then you could look at the huge multi-magnet mounts, combined with a 'base station' type antenna. Then the limit would be the 13'6" vehicle height limit. IMHO probably not worth the effort; as you drive around the gain would only help you sometimes, and hurt you other times, as the car moves on slopes and the like.

    If you are willing to get really complex, then you can get more usable gain by using multiple antennas and electronic beam steering. Build a suitable system, and it could automatically point the beam in the direction of your QSO, and adjust for car motion. I leave the implementation as an exercise for for the reader :)

    73
    Jon
    AF7TS
     
    KW6LA, W2TB and K4AGO like this.
  9. W2VW

    W2VW Ham Member QRZ Page

    I spent about 9 years of 5 day a week commute operating mobile mostly on 146.52.

    Originally used a homebrew 1/4 stick affixed to an NMO centered on the roof of my '81 Coupe Deville.

    Later switched to a 5/8th commercial antenna. Same mounting. No difference noticed.

    Last year of this commute was done with same 5/8ths antenna on a magnet mount because I switched to a 1980 Fleetwood Coupe and did not want to molest the roof.

    Some here might have more experience.

    Not sure what posters are talking about as far as losing certain directions due to gain. As you probably already know, the supposed extra gain from a 5/8th over a 1/4 wavelength antenna usually comes from compression of the donut shaped radiation pattern. Useless higher angle radiation is reduced and useful lower angle radiation increases.

    If your roof is only 5 square feet forget this. Mounting on a deck lid or some other off center configuration would be reason for testing of directionality.

    Mobiling in urban areas, surrounded by RF obstacles may work better using a 1/4 wavelength antenna as high angle operation helps get around the problem. I have seen the extreme of this operating from 48th street in Manhattan while awaiting the price of parking to change tiers at 4AM.
     
  10. KF5FEI

    KF5FEI Ham Member QRZ Page

    Higher gain = taller antenna.

    Taller antenna + mag mount = stopping to reattach mount when a tree limb knocks it off.

    Mag mount getting knocked off car = busted antenna and dents in car.

    Look into a trunk lip mount. You can protect the area on the outside of the trunk with some 3M rock chip stuff. Diamond and Comet make some mounts for SO-239 and NMO that will leave nary a mark on the car.
     
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