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. K0BG

    K0BG Platinum Subscriber Platinum Subscriber QRZ Page

    David, you're correct about realigning the pattern, or donut as you refer to. However it depends on how you reshape that donut. In some cases, you end up with radiation patterns which look like a silhouette of an open hand. Almost all of Diamond's VHF gain antennas have the issue to some extent. Larsen's NMO2/70 looks fairly good on 2 meters, but does have a minor null on 70 cm (≈.5 dB).

    While we're speaking of gain, all of the Pacific Rim antenna companies use dBi instead of the more standard, dBd. Unless you know the difference, it appears their antennas are better (gain wise) than the US brands, when the reverse is true.
     
    K4AGO and N8EKT like this.
  2. KC0BUS

    KC0BUS Ham Member QRZ Page

    What's the most important attribute then? I was looking for as high gain as possible because I'm only running a VHF handie talkie putting out 5 watts on high power setting. And that's on high power setting. I may need to hit a repeater 80 miles away in an emergency, and that's not getting the job done.
    I use a magnet mount because it is temporary. There's always a need for a temporary mounting option.
     
  3. AF7TS

    AF7TS Ham Member QRZ Page

    IMHO if your design requirement is 'need to be able to hit a repeater 80 miles away using an HT in an emergency', then a mag-mount omni antenna is probably not your best option. A hand held yagi in the trunk would probably serve better (well removed from the trunk and connected when actually needed *grin* ).

    -Jon
     
    KK7AMB, KD2ACO, W1VT and 2 others like this.
  4. K0BG

    K0BG Platinum Subscriber Platinum Subscriber QRZ Page

    As I stated earlier, the HAAT is an important consideration, because it establishes the optimal radiation angle. When operating through a repeater, 99% of the time, a simple 1/4 wave antenna properly mounted, will opt perform any gain antenna. This article (used by permission of the author), http://www.k0bg.com/images/pdf/mobile_vhf_ant.pdf, explains the issue.

    There is another issue. Handhelds typically use so-called Rubber Duckies. Their front end gain is set to a very high level to make up for the resistive losses these antennas have. When connecting them to decent mobile antennas, the usual result it a whole lot of intermod. Some handhelds have attenuators built in to help alleviate the problem, but most cheap ones (from China?) do not.

    Adding insult, seemingly all newcomers to amateur radio think they need DC to daylight frequency coverage, and thus buy radios which offer wide-range receive coverage. As a result, radios so designed (handhelds notwithstanding) have wide front ends. Meaning, anything within their bandpass effects their receive capabilities, even if the offending signal can't be heard, or even tuned in!
     
    AI7PM likes this.
  5. AD5MB

    AD5MB Ham Member QRZ Page

    a high gain mag mount is like jogging while breathing through a straw.

    the ground plane is half of the antenna, and the foundation of the system. a magmount is a foundation of sand.
     
  6. W2VW

    W2VW Ham Member QRZ Page

    This brings up a valid point. At 2 meters the amount of capacitance to the car body provided by the magnet mount I used was enough to equal the SWR behavior when NMO mounted. Same shape roof, different car. On longer wavelengths things might be different. My car also had very thin paint.

    Someone with a smaller footprint magnet and thicker paint could have a lot less capacitance and the feedline might start to become part of the antenna.
     
  7. K1FBI

    K1FBI Ham Member QRZ Page

  8. N8EKT

    N8EKT Ham Member QRZ Page

    A 1\4 wave chrome dome whip on a 3\4 inch hole mount is hard to beat.
    But if i was forced to use a magnet mount, the Larsen NMO270B would be my choice because it is a 1\2 wave on 2 meters and won't be as affected by the lesser ground plane of the mag mount
     
  9. K0BG

    K0BG Platinum Subscriber Platinum Subscriber QRZ Page

    There is no AVERAGE mag mount with respect to additional ground loss. Obviously, they work better as the frequency increases, but may vary for what should be evident too.

    The only mag mount I ever tested, was one from MFJ, which was not quite 6 inches in diameter. At 145 MHz, the lost was ≈8Ω when mounted dead center on the roof of my Ridgeline. A through hole NMO mount would be difficult to measure, as the ground loss would be virtually zero. The choice is obvious!
     
  10. W1VT

    W1VT Ham Member QRZ Page

    The problem with HT receivers is that they are designed for long battery life, rather than high dynamic range. You get a better receiver by designing amplifiers to handle more power, which requires more current draw from the battery. Consumers won't buy HTs if the battery life is short. The cheap HTs are cheap because they are designed and sold in huge quantities to the Chinese home market.
    You should test your antenna to make sure it actually resonates in the ham band. Many do not. This may be a good club meeting activity--testing HT antennas to see which ones aren't even designed for use in the ham bands.

    A small rear mount Yagi and mast with a drive on mount is likely to be the best antenna for long distance emergency communications. Ideally you would drive to a good high spot and park, then set up the Yagi. Height makes a big difference in the range you can get. As does finding a path clear of obstructions.
     
    Last edited: Mar 24, 2018

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