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Thread: Antenna placement effects on power output

  1. #1

    Antenna placement effects on power output

    http://kv5r.com/ham-radio/mobile-antenna-placement/

    I found this page pretty neat. The Things its showing are not universal of course but still good info.
    -3db more or less equals a 50% decrease in power

  2. #2
    I'd love to mount mine on center of the roof, but I'm not sure how that would do with my roof rack.

    Right now I receive great, but I feel my tx could be better. Maybe I'll look into moving it.
    2005 Lexus LX470 - Stock for now...

    1998 Toyota 4Runner SR5 V6 4x4 + a bunch of goodies. Lifted, Locked, Illuminated and Armored. Winner,"Best Offroad Truck" - 2010 Pismo Jamboree. It's been upside down and still drives me to work.

  3. #3
    On KV5R and some other pages there is some info on db. For the most part db are like HP on things from vacuums to compressors. What isn't explained in most products is the dbd or dbi. They are different and can be determined by the antenna placement and ground plane or lack there of.

    I was recently in the market for a couple new antennas. I wanted a dual band with higher gain. After researching it seemed my ultimate best bet would to use both of my already installed NMO mounts for a single 2m antenna and a single 70cm antenna with a duplexer. Running such a set up would get around the short cuts a lot of manufacturers use in dual band antennas and their coils. It was explained that they are cheating physics and wavelength is a real world player in the game.

    As such I get best results from a single 1/4 wave 2m antenna (Larsen NMOQ, tuned to 147 mhz) as I have the necessary ground plane. My B-10 dual band antenna does the job for both bands but has zero gain on 2m. I've learned this is not a problem for most of my radio use. In the real world my 5/8 wave 2m whip shouldn't be much better for most situations than the 1/4 wave.

    Sean, I think that your high mounting location and with the Larsen 2/70 you've got a great setup. The 2m portion of the 2/70 is 1/2 wave which doesn't require a ground plane (which I believe your rack is lacking). As a backup/spare/alternative look into just a 2m, 1/2 wave antenna. It might be a little shorter than the 2/70 but just mono band and you don't have to worry about the ground plane. Most soft top/roll gaged/tire swing mounted antennas should be 1/2 wave. Here is a good example: http://www.ruggedradios.com/index.ph...roducts_id=416

    Another thing to consider is the power you're sending through a whip. Higher power can cook a whip in short time. Higher quality antennas last longer and do better but over time they lose their structure due to heat.

    Antenna location can determine radio performance. The mount and antenna also play a roll. This is copied but most explanations are about the same:
    "Gain is reported in two general units, dBd and dBi. They differ from where the point of reference is. dBd is just over 2 units smaller than dBi when the exact same thing is being reported (it's kinda like feet vs meters). If they don't indicate what unit they're reporting the values in, assume it's dBi so you don't get fooled into getting the lower gain antenna after the marketing folks do their magic.

    dB gain is an important spec on an antenna, but don't get too caught up in the "bigger is better" mess. 3 dB = double the signal, 6 dB = 4 times the signal, etc. That sounds like quite a bit of additional signal doesn't it? The fact is that 1 "s" unit (the values on many signal strength meters are shown in "s" units) is 6 dB. The extra 3dB will only change a weak signal from extremely noisy to very noisy. A strong signal will change from fully quiet to ... wait for it ... fully quiet (yes, no change at all).

    The additional signal may even make things worse if you're in an area of heavy RF. The strong signals may mix together giving you what's called intermod, a signal being received on a frequency where it isn't actually being transmitted.

    Generally a "no gain" antenna would be 0 dBd or 2 dBi. 3 dBd is generally pretty modest while 6 dBd is fairly high (on a mobile antenna)."

  4. #4
    Sean we've got to try some more tests. On 395 I stopped receiving you around the same time as the hand helds. Of course that was miles and much better then cb.. . We oughta check it again some time. About the time I lost you I tried Keller peak and got 5x5. That's apples and oranges but if everything checks good we can still use far away repeaters to make up for a possible line of sight issue.

  5. #5
    I'd like to get a meter on my setup and see what I'm getting. Might need to adjust the antenna. I still need to get a short antenna for the tighter trails, too.
    2005 Lexus LX470 - Stock for now...

    1998 Toyota 4Runner SR5 V6 4x4 + a bunch of goodies. Lifted, Locked, Illuminated and Armored. Winner,"Best Offroad Truck" - 2010 Pismo Jamboree. It's been upside down and still drives me to work.

  6. #6
    K0BG is another great source. Here is an applicable link.

    http://www.k0bg.com/myths.html

  7. #7
    Forgive me first of all. I am very ignorant on this subject as said before. I have installed CB in my 4runner already. What are the advantages of HAM over CB besides distance? I know about the license but beyond that it's all greek to me I'm afraid.
    98 3rz 4x4 5spd- Monstalined, 99 Talls, 4.30 E-locker, Extra Lights
    In Progress:
    Tundra/Rear Disc Brakes w/parking brake
    Roof Rack/Rear Ladder
    Sliders
    1st Gen Rollbar Shelf

  8. #8
    clarity is the best part I think in respect to 4x4 use. The repeaters and great distance are wonderful but understanding everything that people are saying because the voices are clear is awesome.

  9. #9
    I'd say 3 things: As Troy mentioned, Clarity and Range. Also, a distinct lack of asshats. You don't typically have people pumping thousands of watts of power cussin' and fightin' on the airwaves. It is a much more civilized place.

    Also, so many more channels. Hundreds (over 70cm and 2m bands) compared to the 40 on CB.

    You can also get small, inexpensive handheld units that don't suck, unlike handheld CB radios.
    2005 Lexus LX470 - Stock for now...

    1998 Toyota 4Runner SR5 V6 4x4 + a bunch of goodies. Lifted, Locked, Illuminated and Armored. Winner,"Best Offroad Truck" - 2010 Pismo Jamboree. It's been upside down and still drives me to work.

  10. #10
    Quote Originally Posted by Seanz0rz View Post
    I'd say 3 things: As Troy mentioned, Clarity and Range. Also, a distinct lack of asshats. You don't typically have people pumping thousands of watts of power cussin' and fightin' on the airwaves. It is a much more civilized place.

    Also, so many more channels. Hundreds (over 70cm and 2m bands) compared to the 40 on CB.

    You can also get small, inexpensive handheld units that don't suck, unlike handheld CB radios.
    You had me sold at the reduction of asshats lol. I will go do some reading and see how much a mobile setup might run.....or maybe a handheld. I have no idea.

    I am guessing my firestik 4ft will not work with ham?

    stamped and snail mailed
    98 3rz 4x4 5spd- Monstalined, 99 Talls, 4.30 E-locker, Extra Lights
    In Progress:
    Tundra/Rear Disc Brakes w/parking brake
    Roof Rack/Rear Ladder
    Sliders
    1st Gen Rollbar Shelf

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