Tough car to stick an antenna on, ideas?

Discussion in 'Mobile Radio Systems' started by KF2Q, Feb 16, 2015.

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  1. AG6QR

    AG6QR Premium Subscriber QRZ Page

    I'd go with a 1/2 wave antenna that doesn't rely on a ground plane, instead of trying to figure out how to put enough metal on your car to make a 1/4 wave antenna work. I have a Diamond NR770HB, which is designed on this principle (I see another recommendation for the NR770HNMO, which is essentially the same antenna with a different mount).
     
  2. K0BG

    K0BG Ham Member QRZ Page

    Lets talk about these ground-plane-less antennas.

    RF MUST return to its source. It will do so over the path of least resistance. In any single element antenna, this will be back down the outside of the coax shield as common mode current. While you can choke part of the CM off, and turn it into heating the choke, the coax still radiates. In most cases, the feed line does most of the radiating, especially in the case of the glass mounted ones.

    Common mode is always higher when using mag, clip, and lip mounts, due mainly to the increased ground plane losses. While VHF ground losses may be low (≈2Ω), HF ground losses can easily exceed 20Ω. The fact you can still make contacts, or have a low SWR, or the ability to hit repeaters, or whether the CM causes any RFI, doesn't mean squat!
     
  3. KK6GMN

    KK6GMN Ham Member QRZ Page

    If all I need to do is hit my local repeaters and I can do that, and I am not stressing the TX, not causing feedback or issues in the cars electrical or computer systems, why do I care? If it works it works. No, it is not optimal, but who cares? If I could do the same by dragging the coax on the ground behind the car I would give it a try.

    Now, if I were in a place were I needed to squeeze every last drop of radiation out of my system to hit something, I would do it differently. Why is it wrong to let the requirements drive the project, not the optimal setup?
     
  4. KK4YDR

    KK4YDR Ham Member QRZ Page

    Its not wrong. And Alan k0bg is not yelling at anyone. He is simply reminding everyone of proper antenna and RF theory. What people choose to do with said theory is up to them. This is a hobby. Consider the more informed you are the better at troubleshooting you will be, and you will remember where you chose to violate or work against the grain of the theory or laws of physics concerning light radiation i.e. R.F.

    There are people who get on here and say... your just an idiot CBr and you suck. Those are just plain ignorant people. Ill defend Alans technical prose as considerate but concerned that people should be aware of the proper theory. Before choosing to violate the establiahed and well researched methods for proper RF generation, transmission, and reception at least try and understand it first. Trust me it will save a lot of money and headache when something doesnt conform to your vision or concept when violating established scientific law and theory.

    My statements are a general address. Not to a specific person or persons.

    A good way to think about it is this way... all RF is light, and it is by laws of physics, all electromagnetic radiation is light waves/wavelengths of transmitted light energy. The frequencyies that VHF is made of are not visible to the human eye. However, given they were, imagine your car/truck and you key up and start talking ... is your whole car emitting light? Is your antenna the only thing giving off visible light? Is your coax making the driveway glow? I for one want as little light to emit from my truck as possible and maximize what I would see from my antenna above the CM choke as possible. Is it easier to see a warm 500lumen glow from a flourescent camp light from 30 miles away compared to a highly focused and intensely optimized 500 lumen spot light? Basically the best visual I can think of. Sure your groundplane etc.. would natuarally emit light but it would be like a dyed smoke leakdown test on an engine. We try to surpress or correct leaks in an engine because they degrade or inhibit function. Hence why we apply proper theory to amatuer radio just the same.
     
    Last edited: Feb 19, 2015
  5. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    Why not just use a whip inside the car? Seriously...with a hand-held/rubber duckie combination on my 2m HT I can work about nine repeaters "full quieting" almost anywhere within 20 miles of my home.
     
  6. KK6GMN

    KK6GMN Ham Member QRZ Page

    I would except the ducky antenna gets in the way and it is harder to read the display. (smirk)
     
  7. KK4YDR

    KK4YDR Ham Member QRZ Page

    Just stick a small magmount on your engine block hahaha now im just being crazy. But knowing Fords econo cars that block is probably made of recycled water bottles.

    You can always use echolink through your car stereo bluetooth using your phone. There are expensive towers everywhere just for your cell phone haha. Good luck.
     
  8. N7EKU

    N7EKU Ham Member QRZ Page

    OT but I beg to differ,

    Ford's got one of the best small automotive engines on the planet:

    http://jalopnik.com/why-fords-tiny-1-liter-3-cylinder-is-the-future-of-ga-1543662936

    73,


    Mark.

     
  9. KK4YDR

    KK4YDR Ham Member QRZ Page

  10. AC7NT

    AC7NT Ham Member QRZ Page

    Talk about path of least resistance... 2m and 70cm working repeaters in local area on a Handheld.... I LIKE IT! The local cops - not so much. They are getting on everyone about operating comms gear while operating a moving vehicle.

    Back to it - hood / trunk mounts are prefered IMO over glass or mag mounts. Eaiser to accompish than surface mounting on roof, and less prone to damage or accidental removal by parking structures and other overhead restrictions. With performance that is margianlly less than with surface mounts, eaiser installation path, and less damage to vehicle (resale value) what is not to like?

    If my Chevy would allow me to use a "standard" NMO mount on the fender I would not hesitate. As it is right now, that option does not exist. I am talking with a local fab shop to see how affordable a "custom" mount would be to produce one for a right side application of the same mount I have on the left of my rig. It bolts to the body front pillar of the door frame, is solid and has a good path to ground without drilling holes. COAX run will be a snap and less restrictive than trying to drill out a roof mount.

    Cheers.
     
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