Two meter mobile antennas for what it is worth

Discussion in 'Mobile Radio Systems' started by N7WR, Jul 26, 2020.

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  1. N7WR

    N7WR Premium Subscriber QRZ Page

    Over the years I have accumulated a LOT of vhf mobile type antennas all with NMO mounts. 1/2 wave. 1/4 wave, 5/8 wave---just a bunch of them.

    I recently decided to use an L shaped mount in the seam between the hood and fender on the driver's side. Anything on top of my pickup truck would have to be removed to get it into the low ceiling carport. So using the L bracket with NMO mount means that there is literally no ground plane directly beneath the antenna.

    For local repeaters all of my antennas worked "OK" but checking the SWR they were not particularly good. None of the antennas with 65 watts from my 2 meter radio would access distant repeaters even though I was parked at 4100 ft AGL with no obstructions.

    So I pulled out my old (at least 20 years) Larson 2/70 and tried it. That antenna has been beat to heck in the woods banging into tree branches but has never failed. Lo and behold I can now access repeaters 75 miles away and the SWR is 1:1 across most of the 2 meter band. I have recommended this antenna in the past and have even more reason to recommend it now
     
    NL7W and N0TZU like this.
  2. AI7PM

    AI7PM Ham Member QRZ Page

    The 2/70 is half wave on VHF, so the plane is not as important. Best of the dual band antennas out there.
     
    KL7KN and N0TZU like this.
  3. M0GVZ

    M0GVZ Ham Member QRZ Page

    It is if you understand rudimentary physics. All end fed antennas require a RF ground, Kirchoffs Law is the applicable physics here.
     
    N0TZU likes this.
  4. N0TZU

    N0TZU Platinum Subscriber Platinum Subscriber QRZ Page

    Yes, but for the end fed half wave antenna the counterpoise current is very low compared to a quarter wave and it doesn't need the large "plane" to efficiently launch a wave.
     
    AG6QR, W7EDC, KX4O and 1 other person like this.
  5. AI7PM

    AI7PM Ham Member QRZ Page

    ..."plane is not as important" vs not needed would be two different phrases. I did not state an RF ground was not necessary, but that a ground plane (meaning 19 inches plus in all directions) was not as important. Yeah, common mode and a radiating shield would result. A half wave mobile antenna mounted on to a metal surface would, in fact, have the RF ground you address, but not necessarily ideal "ground plane".
     
    KX4O likes this.
  6. K2IGO

    K2IGO Ham Member QRZ Page

    I want to know how he parked his vehicle at 4100 feet above ground level.
    Maybe meant MSL ?
     
    KB0MNM and AG6QR like this.
  7. KB0MNM

    KB0MNM Ham Member QRZ Page

    He was referring to elevation ( above sea level ), as is better stated in his profile. It would require a tower platform 4/5 mile high for the ground reference at his site, yet relative to folks at sea level- he already put that elevation in the profile. Folks who live in the city that is a 'mile high' ( Denver, Colorado ) frequently note that strangers can have difficulty with their cars and their own breathing due to altitude. No mention was made of 'take-off angle' from the small whips. The website that W0BG maintains covers some of the directional properties of mobile antennas on a horizontal plane. In this case, a slight vertical angle of the vehicle might effect the ability to get good signals *into* far-off ( 75 miles ) repeaters, as would wet trees.
     
  8. K2IGO

    K2IGO Ham Member QRZ Page

    I assumed that was what he meant, even hinted at it. But that isnt what he wrote.

    altitude =/= elevation
     
  9. KF5FEI

    KF5FEI Ham Member QRZ Page

    Well, the Tram 2m antenna on my van worked exceedingly well, mounted on the mirror -- but I did have to ground the door to get the SWR reasonable. Never could get the Larsen I bought to work. Finally exchanged the Larsen as defective, then sold it for cheap to a friend.
     
  10. KA3TJI

    KA3TJI Ham Member QRZ Page

    Yep, and that is why I have the 2/70B on all my vehicles including my two bikes. Best damn antenna ever made.

    [​IMG]
     
    WF7A likes this.

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