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Thread: Need advice on antenna/mobile set-up

  1. #1

    Default Need advice on antenna/mobile set-up

    Hello,
    I am relatively new to these radios. I got licensed and bought a KENWOOD TM-281A for my truck. We use them for hunting and communicating. When I bought my radio, the salemans recommended a Hustler brand magnetic mount set up for my band (144). The setup worked fantastic for a few years. Then I traded my truck in for a new F150 with an aluminum body. So, the mag mount no longer works. I wired it directly to the battery as I had it before. I purchased a mount that goes on the drivers side front fender - just remove a hinge bolt and bolt it down. I bought a tram NMO style antenna. Granted, it is shorter than my previous whip style antenna but it doesn't work well at all.

    I've been reading about ground plane and perhaps the antenna worked better on top of my vehicle. I don't want to drill in the roof of the truck either. So, here come a bunch of questions:
    Could it be a ground plane issue? I saw some Larsen antennas advertised as non-ground plane, would they work better?
    Should the mount be grounded? If so, how?
    Anything else I'm missing or any other thoughts to improve performance? I would like to get a taller antenna to replace the shorter Tram unit I have now.

    Thank you in advance.
    Joe

  2. #2

    Default

    If you take a piece of string 100' long and you tie the string to the antenna and walk around the truck with the string fully extended in a circle, using a Field Strength meter, you would see that the antenna now talks best in the direction with the most mass - metal. So if you mount it to the right front fender, the portion of the signal with the most strength is now directed towards the left rear of the vehicle. Probably one reason why so many 102 inch whips for 11 meters was mounted on the right rear quarter panel of most of the larger family vehicles when I was a kid. It allowed the operator to talk best towards the direction the vehicle was traveling to, not behind the vehicle - back towards the direction the operator was traveling away from..
    The best location is always going to be the middle of the vehicle - period. Most antenna situations are a compromise - what the user is willing to tolerate, not what works best! My first question would be - how did you tune the antenna, after you mounted it to the vehicle.. If the antenna was resonant - 1:1 SWR - the length of the coax wouldn't matter. then again, if there is 12 feet of coax from the PL connector to the NMO connector - what do you do with the left over coax? Did you coil it up? That creates a choke! Did you know this? My advice is for you to find a 2 way radio shop, have the antenna installed professionally, pay someone to install it for you.. The simple mag mount antenna - that required no investment on your part of any type of understanding - how a antenna works, or how SWR affects your transmit signal, now has come back to bite you.. The days of playing cb radio, or playing with a handheld - because all you have to do is press the PTT button - leaves us with a whole new group of unskilled operators that doesn't know anything about the hobby they chose to participate in... ( Basically we dumbbed everything down to the point of where they don't understand what happens when they press the PTT button or how to tune a antenna when it is installed)...

  3. #3

    Join Date
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    Default

    Quote Originally Posted by Sixmeters View Post
    If you take a piece of string 100' long and you tie the string to the antenna and walk around the truck with the string fully extended in a circle, using a Field Strength meter, you would see that the antenna now talks best in the direction with the most mass - metal. So if you mount it to the right front fender, the portion of the signal with the most strength is now directed towards the left rear of the vehicle. Probably one reason why so many 102 inch whips for 11 meters was mounted on the right rear quarter panel of most of the larger family vehicles when I was a kid. It allowed the operator to talk best towards the direction the vehicle was traveling to, not behind the vehicle - back towards the direction the operator was traveling away from..
    The best location is always going to be the middle of the vehicle - period. Most antenna situations are a compromise - what the user is willing to tolerate, not what works best! My first question would be - how did you tune the antenna, after you mounted it to the vehicle.. If the antenna was resonant - 1:1 SWR - the length of the coax wouldn't matter. then again, if there is 12 feet of coax from the PL connector to the NMO connector - what do you do with the left over coax? Did you coil it up? That creates a choke! Did you know this? My advice is for you to find a 2 way radio shop, have the antenna installed professionally, pay someone to install it for you.. The simple mag mount antenna - that required no investment on your part of any type of understanding - how a antenna works, or how SWR affects your transmit signal, now has come back to bite you.. The days of playing cb radio, or playing with a handheld - because all you have to do is press the PTT button - leaves us with a whole new group of unskilled operators that doesn't know anything about the hobby they chose to participate in... ( Basically we dumbbed everything down to the point of where they don't understand what happens when they press the PTT button or how to tune a antenna when it is installed)...
    Six meters... Why does it seem like you talk down to everyone you meet? You lose on every teaching moment I see you engage in due to your "get off my radio lawn" demeanor. You had it great up until the colored highlights in your post. He wants to know what he's doing wrong and how to do it right; not be told to take it to a radio shop to let the 'priests of syrinx' do it for him. You had to learn once too and you aren't paying it forward very well, IMO.

    Just help the guy a little and keep the 'tude on USA 75 meters where it comes from, m'kay?

    Investigate this site for excellent advice on mobile setups; be prepared to read! http://k0bg.com/
    Last edited by WZ7U; Wed 22nd Aug 2018 at 08:20.

  4. #4

    Default

    Quote Originally Posted by WZ7U View Post
    Six meters... Why does it seem like you talk down to everyone you meet? You lose on every teaching moment I see you engage in due to your "get off my radio lawn" demeanor. You had it great up until the colored highlights in your post. He wants to know what he's doing wrong and how to do it right; not be told to take it to a radio shop to let the 'priests of syrinx' do it for him. You had to learn once too and you aren't paying it forward very well, IMO.

    Just help the guy a little and keep the 'tude on USA 75 meters where it comes from, m'kay?

    Investigate this site for excellent advice on mobile setups; be prepared to read! http://k0bg.com/
    Well said.

  5. #5

    Default

    If it's the BR-150B, it should have come with a tuning/cutting chart. If you don't have an SWR meter, maybe you could borrow one long enough to get the antenna working.

    Ben

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