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GMRS Radio Antennas - Ground Plane?

Discussion in 'Technical Chat' started by nartmot, Jul 9, 2020.

  1. Jul 9, 2020 at 6:05 PM
    #1
    nartmot

    nartmot [OP] Well-Known Member

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    Hey guys, I am just learning about radios and I decided to purchase a Midland MXT275 GMRS radio. Ideally, I would like to mount the antenna on a Relentless Fabrication Hood Hinge Mount (pictured below). I dont want to drill into my roof or hood and dont like the idea of a magnetic mount. However, I started reading about ground planes and am totally confused now. Do I need a non ground plane antenna to use this as a mounting point? Will a NGP or GP antenna give me better results in this location? Thanks.

    [​IMG]
     
    Last edited: Jul 9, 2020
  2. Jul 9, 2020 at 9:11 PM
    #2
    cwadej

    cwadej Ballerina Award winner

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  3. Jul 10, 2020 at 7:43 AM
    #3
    Naveronski

    Naveronski Well-Known Member

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    Non-ground plane antennas will perform better when you do not have a true ground plane.

    For example, I wanted to put an antenna on my roof rack. Highest point on the truck, but I did not want to cut into the cab.
    This has worked very well for me:
    https://www.arcantenna.com/trab4500n-m2m-400-490-mhz-black-low-profile-omni-antenna.html
    (edit: if you're going to shop around, make sure the model number is still the TRAB4500N. The "N" matters.)

    And it wasn't terribly expensive.
     
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  4. Jul 10, 2020 at 11:31 AM
    #4
    nartmot

    nartmot [OP] Well-Known Member

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    Thanks, guys. I seem to be getting some mixed answers on this question so still pretty confused. I also reached out to customer support at RFWiz.com and they pretty much told me that a GP antenna would be optimal with this bracket, provided the hood is metal and the bracket makes good contact with it. Any thoughts on this?
     
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  5. Jul 10, 2020 at 11:38 AM
    #5
    2013XSPX

    2013XSPX Well-Known Member

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    I have a QWB450 antenna on my MTX-400. I have it mounted using the NMO on my Prinsu rails. I think I would benefit from a non-ground plane antenna or putting the 450 on a plane.
    Pelican_Vault.jpg
     
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  6. Jul 11, 2020 at 3:05 PM
    #6
    nartmot

    nartmot [OP] Well-Known Member

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    Last edited: Jul 11, 2020
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  7. Jul 12, 2020 at 5:00 AM
    #7
    synaps3

    synaps3 Wag more bark less

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    It's on the truck and the truck is acting as the reflector / ground plane. The hood is a huge half of that ground plane, and the rest of the truck is the other half on the other side. You would have been fine and a bit better with a GP, but the NGP will still work fine - you'll just get a bit less transmission strength.

    An NGP antenna is typically used on top of a non-metallic roof rack or top of a fiberglass camper shell, but you more commonly see them on motorcycles from my experience. I have my CB and HAM antennas both on my (metal) roof rack and I use GP antennas with both with acceptable SWR. My SWR was even better when I had them on a hood mount like yours, but I couldn't stand the wind noise.

    In either case, make sure you tune the antenna for the proper SWR. You definitely want it below 2, the closer to 1 the better.

    Firestik is very reputable - this is a good read for you: http://www.firestik.com/Tech_Docs/GP-or-NGP.htm
     
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  8. Jul 16, 2020 at 10:30 PM
    #8
    JJ04TACO

    JJ04TACO Well-Known Member

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    I am ditching the CB for GMRS. Probably going with a 50x1 from Btech for the mobile. I have Midland handhelds and love them, but the price of their mobiles are too much for the higher watt units like the MTX400. That said those of you who have them, how have they been?

    I think I'll use Midlands 6db gain GMRS antenna however...and/or their 3db stubby looking one.
     
  9. Jul 17, 2020 at 12:20 PM
    #9
    nartmot

    nartmot [OP] Well-Known Member

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    I read several reports that the 6db Midland antenna is too short to be tuned properly. Look into a quality antenna from Laird, Comtelco, Diamond, or Larsen to get the most out of your radio.
     
  10. Jul 17, 2020 at 5:37 PM
    #10
    JJ04TACO

    JJ04TACO Well-Known Member

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    Awesome! Thanks. I’ll look into those for sure. I need an SWR meter for tuning as well. I thought that GMRS didn’t require much if any tuning.

    I’ll be mounting it on a front finder mount from CBI. It that makes a difference...
     
  11. Jul 18, 2020 at 6:31 PM
    #11
    JJ04TACO

    JJ04TACO Well-Known Member

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    So I looked at all those antennas and I have NO clue which is even close to what I need. I saw nothing in the 462-468 MHz range or that was noted for GMRS. If you can point to one directly that would be a start...:facepalm:
     
  12. Jul 18, 2020 at 6:58 PM
    #12
    nartmot

    nartmot [OP] Well-Known Member

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    450 - 470 is what you want for GMRS. The one I linked above would be good for no ground plane. For general use, you will probably want to tune your antenna to about 464.5mhz. Not sure about the other brands but Laird, and I believe Comtelco, come with a chart that tells you how much antenna to trim to get a certain frequency, so you might not even need a SWR meter unless you want to be really precise.
     
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  13. Jul 19, 2020 at 6:39 PM
    #13
    JJ04TACO

    JJ04TACO Well-Known Member

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    May I switch gears? So where do you guys find a 20A switched source for wiring your radios? The fuse taps are usually rated for 15A and 14g wire. Should be 12g for 20A. So i'll need a good place to tap into.
     
  14. Jul 19, 2020 at 9:25 PM
    #14
    nartmot

    nartmot [OP] Well-Known Member

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    Its probably better to wire your radio directly to the battery to minimize electrical noise and interference. If you want it switched, you will probably have to add a relay. My MXT275 only draws 3 amps so I don't have to worry about that. Not sure about your setup but the MXT400, which is 40W only draws about 10 amps and comes supplied with a 15 amp fuse.
     
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  15. Jul 19, 2020 at 10:50 PM
    #15
    JJ04TACO

    JJ04TACO Well-Known Member

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    The 50X1 instruction manual says it has a 20A max draw. I'd prefer not to do direct to battery because I know it will be left on. My kids can't help but push every damn button imaginable.

    That said, I wouldn't mind doing a Blue Sea or Busman for future stuff, but I just don't want to do all that for this.
     
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  16. Jul 20, 2020 at 4:07 PM
    #16
    JJ04TACO

    JJ04TACO Well-Known Member

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    Well, I compromised. I did an AMP-U25 from BTech to boost the power of my GMRS V1 handheld. I did get the antenna you recommended as well as the proper cable. It comes with an adapter that screws into the antenna port of the handheld. Should get 25 watts maybe more plus the benefit of the antenna. A lot cheaper than another radio setup...
     
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  17. Jul 20, 2020 at 4:16 PM
    #17
    maineah

    maineah Well-Known Member

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    There is quite a lot of myths about ground planes and the higher the frequency the less a ground plane becomes it is a return path back to the radio so a good solid mount basically is all you need. I run 6 to 80 meters in my truck with pretty much nothing left out as you well know the late trucks have a plastic bed my 6-80 meter antenna is mounted on the right rear quarter to the support at the rear of the bed not much of a ground plane there but I have worked the world mobile
     
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  18. Jul 20, 2020 at 4:20 PM
    #18
    nartmot

    nartmot [OP] Well-Known Member

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    Interesting setup. Seems like it will give you a lot of flexibility in terms how you use it (portable vs mobile) and it definitely doesn't hurt that you saved some cash. 25W seems like plenty too. I just want to be able to communicate with my buddies if we get strung out on a trail and I think situations where we are 2+ miles apart would be extremely rare.
     
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  19. Jul 20, 2020 at 4:26 PM
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    nartmot

    nartmot [OP] Well-Known Member

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    You could be right. Maybe it doesnt matter a whole lot. FWIW, I still haven't found a conclusive answer to my question. It has pretty much been a 50/50 split for GP vs NGP and I even posted on the GMRS forums (isn't it cool that there is a forum for any interest you can think of?). @synaps3 's answer was probably the best one since he has experience with the same mount and actually hooked up a SWR meter.
     
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  20. Jul 20, 2020 at 6:43 PM
    #20
    JJ04TACO

    JJ04TACO Well-Known Member

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    Yeah, I can see people getting into the quest for a perfect setup. I compromised a bit in overall wattage. I wanted to max it out at the full 50. But I feel 20-40 seems really good given the quality antenna and clean signal from the amp.

    I can unscrew the antenna cable to the amp and go back to the original handheld one for walking around. The amp was smaller and had a speaker on it too. Plus I have the option to use a mike plugged into the front if I want. Not too shabby.
     
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