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. NM7G

    NM7G Ham Member QRZ Page

    How large was the ground plane when you measured the null, and was the ground plane circular? I measured many dozens of VHF and UHF verticals on outdoor ranges, and some in anechoic chambers. With circular ground planes, any null I saw was due to range error (reflection or leaking range RF cable assembly), RF on the coax cable, or to interference from outside the range.
     
  2. K0BG

    K0BG Platinum Subscriber Platinum Subscriber QRZ Page

    I didn't. You can down load the radiation pattern from Larsen's site.

    Even a slight "dent" in a circular pattern can be called a null. If memory serves, the null I spoke about is about .5 dB which is rather insignificant. Especially so, when compared to some of the Pacific Rim antennas, where 3 dB or greater nulls are seen. If you want some enlightenment, look at the pattern of Diamond's four bander (10, 6, 2 and 70).
     
    K4AGO likes this.
  3. K4AGO

    K4AGO Ham Member QRZ Page

    NMO with a 5/8 antenna is about as good as it gets with an omni dirrectional antenna. Thats what I use.
     
    AG6QR likes this.
  4. K4AGO

    K4AGO Ham Member QRZ Page

    Hitting a repeater 80 miles away with 5 watts is highly unlikely. Of course it depends on your elevation and or the elevation of the repeater. I can hit the Mt. Mitchell repeater from Greensboro, NC which is maybe 100 miles as the crow flies. Then again Mt. Mitchell is 6, 684 feet above sea level and Greensboro is less than 100 ft above sea level (estimated). Maybe you should take along a cell phone for emergencies.
     
    Last edited: Mar 27, 2018
  5. NM7G

    NM7G Ham Member QRZ Page

    I agree entirely with your message about the role of gain in a repeater environment, and also contend that a 0.5 dB null, dip, wobble, whatever it's called, is of no significance except in a controlled lab test. Power from the entire radiated field isn't lost (as in gone away) due to small nulls, because average power remains in the 3-dimensional field. For every 0.5 dB null, there are one or more HIGHER bumps elsewhere in the 3D field. The point I attempt to make is it's important for users of published data to understand how very difficult, labor intensive, and thus costly, it is to obtain flawless data. For typical ham mobile use, published data, out of context with how it was obtained, has limited value and shouldn't be thought of as lab quality. For many of us, the ground plane under our mobile vertical is quite unsymmetrical. That circumstance is enough to distort most azimuthal patterns.

    I don't like mag mounts either, but occasionally use one. It's a pragmatic step. The coax to mag mount interface is frequently a cause for a null, because the symmetry of an otherwise ostensibly symmetrical radiator is distorted by the presence of the cable. Indoors, in lab environments, the current bump at the coax to mag mount junction can be mitigated. However, the mitigating methods employed don't lend themselves to weather resistance nor to eye appeal. 73
    Gary
    p.s.: I'm intimately familiar with Larsen's patterns.
     
    Last edited: Mar 27, 2018
  6. K0BG

    K0BG Platinum Subscriber Platinum Subscriber QRZ Page

    Agreed.

    One thing I think is lost in the translation, so to speak is what gain really is. One would think (from reading the posts here) that the power is increased by whatever gain there is, and we both know that is not the case. Rather, the existing power is redirected, or as someone here mentioned... "the donut gets squashed!". That's (sorta) a true statement.
     
    KW6LA likes this.
  7. WG8Z

    WG8Z Ham Member QRZ Page

    The harder you squeeze the donut the more jelly squirts out. :)
     
    VK6APZ and NM7G like this.
  8. K4PDM

    K4PDM Ham Member QRZ Page

    Nulls don't really matter in vertical antennas since your orientation will be constantly changing, as will the terrain and possible obstructions you deal with.

    If you are trying to hit a distant repeater, say 30 or 40 miles away as is common in my area, the quarter wave just won't cut it.

    One of the problems with ham radio is that some "experts" parrot the same "rules" repeatedly without understanding that there are exceptions and compromises that make his "perfect " antennas less-than perfect in a given situation.

    A tri-magnet mount will support most any high gain VHF/UHF antenna.
     
  9. K0BG

    K0BG Platinum Subscriber Platinum Subscriber QRZ Page

    I question this statement... " the quarter wave just won't cut it".

    I used to live in the Denver, area. I used a 1/4 wave antenna. The repeater I used most regularly was nearly 100 miles (!) away, and I had not problems at all. In my travels, I often used the Kingman peak repeater, and it averaged 200 miles away. All this with just 25 watts. But then again, the 1/4 wave was mounted dead center in the roof. Seemingly, no one want to do that theses days.
     
    AI7PM and NQ9L like this.
  10. M0GVZ

    M0GVZ Ham Member QRZ Page

    I use a 1/4 wave antenna on 2m. It'll easily cover over 60 miles with 10W. There's no point covering more than that because unless you or the other station or both stations are quite high up above sea level then the curvature of the earth gets in the way and blocks your signal.

    Going back to that scenario, if one of you is much higher than the other and not too far away then a high gain antenna will actually give you a WORSE contact than a lower gain one. A friend of mine runs a local repeater and had a customer with trucks with 5/8 wave antennas on. They couldn't get into his repeater barely 10 miles away from them. Changed over to 1/4 waves which I suggested and it was no problem, full quieting. The problem? His repeater was several hundred feet higher than where the trucks were and the horizontal take off pattern of the 5/8 wave antennas meant hardly any of their signal was making it to the repeater. He now fits 1/4 wave antennas to everything.

    So lets say you decide all the above is complete rubbish, take off angle doesn't matter, only the gain does so lets look at the gain. At best between 1/4 wave and the best vertical highest gain monopole mobile antenna after you've disregarded all the marketing BS you're going to have no more than 3-6dB at the very best. That is half to one single S point. It isn't going to make that much of a difference.
     
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