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Antennas and our vehicles (Long)

Discussion in 'Ham Radio - CB - Trail Communications' started by The DB, August 14, 2011.

^^Searches ExplorerForum.com^^





  1. The DB

    The DB Active Member

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    I'm writing this because I have had several PM's asking various questions about antennas and our vehicles.

    The goal of this post is to explain CB antennas and their use on our types of vehicles (SUV's and small pickup trucks). I want to do this without resorting to tons of equations as many people find them intimidating and to some people unreadable.

    This is also meant for the CB band only. Not all of this will apply to other bands. The further away from the CB band you get the less of this information will apply.

    The antenna is the most important part of the cb radio system. CB radios, from $20 through $150 and beyond have their differences, they are however all limited by law to 4 watts of output power. Because of this the antenna can make all of the difference when it comes to range and wether or not you can hear or talk to another station. If you have a choice between better radio and lesser antenna and better antenna and lesser radio, choose the better antenna.

    The choice of antenna can even affect your transmitting range more than "peaking and/or tuning" you radio.

    Several things need to be considered when looking at antennas.

    Positioning:
    - Antennas like to be as high as possible, the higher the antenna the better your range, both transmitting and receiving.
    - Antennas don't like metallic obstructions nearby such as the side of a vehicle. These obstructions affect the radiation pattern and make tuning the antenna more difficult. If you must have an obstruction you want at least 60% of the antenna above it. You will have less receive and transmit range on the other side of that obstruction.
    - If you are running a cophased (or dual) antenna setup you want as much of the antennas with clear view of each other as possible, again no less than 60%. These antennas use each other to create a directional effect to the front and back. These antenna also do not require a ground plane if you have a vehicle with a fiberglass body.
    - The metal body of the vehicle is as important as the antenna itself. This is the ground plane. Optimally the best ground plane on CB frequencies is 9 feet however that is not always possible with mobile setups.
    - Be careful when connecting to a luggage bracket as these are not always grounded to vehicles. My Explorer uses plastic risers to hold up a metal bar. This mounting point is not grounded properly, and while it may still work, it will affect the tuning of the antenna and range.
    - Generally the best location for an omnidirectional (all directions) antenna on either the Explorers or Rangers is the middle of the roof. If you want more range in one direction you move the antenna in the other direction on the roof, for instance, my antenna is more towards the back from center giving me more of an egg shape pattern pointing towards the front.

    Length:
    - To a CB radio, assuming a descent SWR reading, the longer the antenna the better. There is simply no substitute for length. In practical terms the longer the antenna the more unmanageable it is. Some places you go wheeling won't even allow antennas beyond a certain length. Also with a long antenna garaging your vehicle can present an obstacle as well. On the plus side they do make antennas with removable whips and mounts that will bend the antenna down 90 degrees for better clearance. You never want to transmit when the whip is removed or bent down as you can damage your radio.
    - Long story short, the best antenna is often the longest one you can effectively manage.

    Tuning:
    - You want your antenna tuned to as low of an SWR reading as you can get. A reading of 1.5 to 1 or better is considered good, if you can get 1.2 to 1 I would call that great. Unfortunately not all antennas will tune that well and its position as mentioned above can affect this as well. The higher the reading the more power gets reflected back to the radio. Percentages are close to those listed below.
    * 1.5 to 1, 4% power reflected or .16 of a watt (assuming 4 watts transmitted)
    * 2 to 1, 11% power reflected or .44 of a watt (assuming 4 watts transmitted)
    * 3 to 1, 25% power reflected or .75 of a watt (assuming 4 watts transmitted)
    - Some antennas are not tunable, these are generally pretty close to where you need to be as is assuming positioning is not affecting the reading.

    Efficiency:
    - Efficiency is how much energy is lost in the antenna itself, usually as heat.
    - No antenna is 100% efficient. A 102" whip (the only antenna that does not need a load) is about 95% efficient, anything with a load will be less efficient that that.
    - Smaller antennas need larger loads to compensate for the smaller size and are less efficient.
    - The positioning of a load also makes a difference, the optimal place for a load is the top of the antenna, unfortunately this is also not always practicle as the antenna has to be strong enough to support the weight of the load. Center loading is the next best as far as efficiency is concerned, again the antenna has to support the weight of the load. The least efficient but most common location is the base, here they can make the load as big or as little as they need.
    - The smaller the antenna the bigger the load needs to be to match it to the coax, and thus more inefficient.
    - There are some loads that are more efficient than average, these are usually big like the ones on the Predator line of antennas. Some of the longer antennas with this type of load can be nearly as efficient as a 102" whip. Nearly.

    Wavelength:
    - For a vertical antenna the higher the wavelength the more it will transmit outwards from the antenna and the less it transmit up and down
    - Most mobile antennas are tuned to be 1/4 wave antennas, however some are claimed to be tuned to be 1/2 wave or even 5/8 wave antennas. If you don't see 1/2 wave or 5/8 wave in advertising I would assume its tuned to be 1/4 wave.
    - Tuning to 1/2 or 5/8 wave requires a larger load usually making it less efficient, this will nullify at least part (and usually all) of the range gains you would have achieved.

    Quality:
    - In most cases a poor quality antenna won't affect range aside from the items mentioned above, however it is more likely to fail at some point than a better quality antenna. In most cases you get what you pay for, unless you are being scammed by someone.

    Advertising:
    - I have seen some antenna companies claim their antennas (sometimes 4 foot long or less) works just as well or even better than a 102" whip. This is called advertising, and the main goal of advertising is to try and get you to purchase their product, not to tell you the truth.
    - Be careful about personal claims, there are people that had a faulty antenna setup, then replaced it with a cheap antenna that wasn't faulty, and as such it performed much better. They now swear by the new antenna and recommend it to everyone regardless of the situation, even though it really isn't that great of an antenna.

    Fits more than one category above and Other:
    - There are antennas that use a continuous load up the entire antenna. Some people (and advertisers go figure) like to use the full length of wire in some fiberglass antennas when making claims about performance, however the effective physical length of the antenna and not the length of the wire inside is what determines the actual effectiveness.
    - In general the longer the antenna the wider range it covers when tuned. For example, assuming two different length antennas tuned to 1 to 1 SWR on channel 19 (the actual middle frequency of the CB channels) the longer one may have a 1.2 to 1 SWR reading on channels 1 and 40 and the shorter one 1.5. These will vary depending on the antenna length.

    Taking a look at some of the antennas available.

    The 102" whip, the antenna all other mobile CB antennas are compared to:
    - Its not actually a 1/4 wave antenna for CB, its to short. It doesn't become a 1/4 wave antenna for CB until you add a 6" spring which puts its wavelength into the lower portion of the CB frequencies. Without the spring it is better tuned for 10 meter ham radio, however it has a wide enough bandwidth that it is usually around 1.2 to 1 SWR without said spring.
    - If you get one and use a spring make sure you get a heavy duty spring that was meant for it, that is usually the $20 plus springs and definitely not the $5 springs available.
    - Very durable, when I had one on a car I hit many tree branches often pretty hard, this didn't affect the performance of the antenna in any noticeable way.
    - Not very expensive comparatively to set up, although usually requires a little more work as it requires a bracket.

    Predator line of antennas and equivalents:
    - Range in length from 3' to 7'
    - Great pains have been taken (and charged for) to eliminate efficiency issues.
    - Can be intimidating for an inexperienced person to tune as they often come with whips that have to be cut by inches and sometimes feet to tune properly.
    - The longer versions of these antennas perform nearly as well as a 102" whip.

    The Wilson line:
    - I may be biased as I am currently running one myself (Wilson 5000).
    - The Little Willy is a popular budget antenna, you get the quality of the bigger versions in a smaller, less expensive package.

    The K40:
    - I have heard many good things about this antenna, many people swear by them.

    Wilson 1000 vs K40
    - These antennas are the stuff many swear by. Some claim one is better while others claim the other. A friend an I tested them one day, both were at the same SWR reading (1.1 to 1 or better) and located at the same part of the vehicle (one was removed when done and the other put in its place). The meters on both radios on both ends were tuned to be accurate. We were about 8 miles apart. This test was done both as a transmitting test where the test vehicle transmitted and the remote unit measured, and a receiving test where the remote unit transmitted and the test vehicle measured. The Wilson 1000 did slightly better, it wasn't a full s-unit, but was visibly higher for both transmitting and receiving. If it were my money I would get the Wilson (as I mentioned earlier, I have a Wilson product and may be biased), that being said I wouldn't fault anyone for getting a K40.

    Fiberglass Antennas:
    NOTE: I am not a fan of fiberglass antennas, haven't been since I had three different brands break the first time they hit something, and they didn't hit that hard. Maybe it was my bad luck. I have also never seen a fiberglass 10-Meter antenna for sale, and that being a HAM band (near our own) where people are in theory more learned on such things I'm taking that as a sign.
    - Some people swear by them and think they are the best available.
    - There are two different types of these as mobile antennas, some that have most of the wire part of the antenna at the top (forming a top load), and some that the wire is evenly spread throughout (the entire antenna is a load).
    - If it were me I would go more with the top load type, should I ever find myself purchasing one as some continuous loads are very efficient, however most are not.

    The DB
     
    Last edited by a moderator: August 15, 2011
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  3. Scott B.

    Scott B. Well-Known Member

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    Good info.

    Let's make this a sticky.

    Oh, and K40 all the way! :D
     
  4. rizzjc

    rizzjc Scubajoe - Radio Mod Staff Member Moderator Elite Explorer

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    Nice post! I made this a sticky in the forum. Should be helpful to a lot of people. :thumbsup:
     
  5. Lube

    Lube Active Member

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    A lot of what you say is true, and about 99% of it is applicable to any vertical antenna at any frequency.

    I'm curious about your efficiency claim though, and what you're referencing. No vertical gets 99%. And if you're talking about radiation efficiency (which is the only efficiency that matters), it's typically down in the 3% or less range.

    If you want some really excellent education in antenna's, go to http://www.arrl.org/shop/Antennas/ and get a copy of the ARRL Antenna Book. Not cheap, but then knowledge never is.
     
    Last edited: August 15, 2011
  6. rizzjc

    rizzjc Scubajoe - Radio Mod Staff Member Moderator Elite Explorer

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    I don't know where the numbers came from, but I would assume efficiency is referring to the amount of forward power vs. reflected, which has more to do with the antenna being properly matched to the transmitter. I'm not sure what the "3%" refers to either, but it's certainly not referring to the efficiency as I'm thinking of it. Guess I'd better go pull out my ARRL Antenna Book. ;)
     
  7. rizzjc

    rizzjc Scubajoe - Radio Mod Staff Member Moderator Elite Explorer

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    Here is a much more technical discussion of all of the pieces that makes up the overall radiation efficiency:
    http://www.k0bg.com/eff.html
     
  8. The DB

    The DB Active Member

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    An antenna that would have a 3% efficiency or less would be worthless, or are you referring to a 3% or less loss?

    I'm not talking about SWRs and forward to reflected power.

    Efficiency takes whats left of the forward power from SWR as it passes through the antenna and radiates. An antenna is a load, (in addition to any artificial load added to the antenna to adjust for length), and as a load it impedes the AC input that is the radio signal. In the radiating part of the antenna some of this AC input is lost as heat. The efficiency I am referring to is this usually this small loss, and any additional losses in any artificial loads in the form of coils (and/or capacitors depending on the matching network used on antennas).

    I am talking about the efficiency of the radiating portion of the antenna only, not the entire antenna system, and not anything being reflected via SWR.

    The DB
     
  9. The DB

    The DB Active Member

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    This pretty much encapsulates what I was referring to. I did pull the 95% number for a 108" whip (although I did say 102" in the original post) from when I earned some extra money tuning antennas as a side job for a CB shop I hung out at while in college and may have been off a bit. For various reasons I have been out of radio in general for over 10 years. I apologize if my memory is in error. The person I worked for taught me everything I know about antennas. I'm actually surprised as to how much I remember...

    The DB
     
  10. mwweimer_2001

    mwweimer_2001 Member

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    Do you think it would be possible to mount an effective CB antenna on the fiberglass bed of a Sport Trac if an artificial ground plane was installed? I've been throwing around that idea for a while and just haven't been able to figure it out yet.
     
  11. The DB

    The DB Active Member

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    The roof would be the better place. How are you planning on putting on an artificial ground plane?

    The DB
     
  12. 4x4junkie

    4x4junkie Well-Known Member

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    Fiberglass antennas

    Great post :thumbsup:
    Though I felt I needed to comment on this:
    I haven't used anything but fiberglass antennas for maybe the last 25 years or so (currently I have a 8' Francis Amazer atop the roof of my lifted Ranger... You can probably imagine how many trees, drivethrus and gas station overhangs I regularly hit with it lol).
    I think they become vulnerable to splitting if the little rubber (vinyl?) protective cap is lost off the tip (which it is easy to lose too). Since I started wrapping the top 4" of the antenna about 8-10 layers deep with electrical tape, I've never lost another antenna to splitting (the antenna on my Ranger is probably 15 years old now, almost as old as the truck).

    I prefer a fiberglass antenna over a steel whip since it stays more erect when you're going down the highway at 70 MPH, which means you "get out" better. ;)

    One significant downside to fiberglass though... As they weather in the sun, they start to shed fibers (not fun if you get them in your fingers). To combat this I lightly sand it and then shoot a layer of paint over it (a friend of mine put polyolefin shrink tubing over his, which I haven't tried myself yet. Not sure how well the shrink tubing would hold up to hitting things though lol).




    Agreed, I wouldn't mess around with the Sport Trac bed, use the roof. If you're not looking to drill a hole, a magnetic mount is fine, though be sure to get a good quality one, as cheaper ones are more prone to falling off, which could damage things if it strikes the side of your truck as it falls.
     
  13. The DB

    The DB Active Member

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    To each their own, I was just being honest up front saying I had problems rather than just saying fiberglass sucks. There are a lot of people that run them and like them.

    I've tuned both, they tune pretty much the same.

    I wasn't trying to say all fiberglass antennas are bad, and I did mention:
    Hmm, shrink tube a fiberglass antenna... gonna make it look like a big rubber duck...
     
  14. mwweimer_2001

    mwweimer_2001 Member

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    I thought about installing 2-4 radials off the mounting bracket (which would be grounded) creating somewhat of a ground plane at the base of the antenna.
     
  15. The DB

    The DB Active Member

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    A sheet of metal is the best. As far as ground radials go the more the better. Is this going to be down in the bed? Sorry I'm not familiar with the sport track lineup.

    Are you also sure that the fiberglass will be able to not only hold the weight of the antenna your going to use but also any wind loads on it?

    The DB
     
  16. Dan Whitaker

    Dan Whitaker One fast putty tat Elite Explorer

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    Will an antenna be effected by a cloth top? I have a KIA Sportage with a soft top. I have a Firestik I'm going to use and mount it on the rear of the vehicle using a Firestik door jamb mount bracket. I would say the antenna will be about 24" above the roof line with the rest blocked by the soft top.

    The only concern is there is factory roll bar in the back of the vehicle.
     
  17. The DB

    The DB Active Member

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    Make sure you mount it to a metal part of the vehicle. Cloth is not a ground plane and will not work as such, aside from that it will have minimal if any effect on the antenna.
     
  18. 4x4junkie

    4x4junkie Well-Known Member

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    I figured you were being honest, I was just giving my experience as well after finding out what caused them to become more fragile when it strikes things.
    I've got a 5' Francis on my Bronco II and same thing, no issues after having wrapped the tip up in tape.
    :chug:

    Actually you couldn't even tell it had been shrink-wrapped unless you walked right up to it and saw where the two pieces of tubing overlapped each other slightly (making it about 1 mm bigger in diameter at that spot).
     
  19. dbfreak22

    dbfreak22 New Member

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    i have a 02 sport track and im having trouble finding a way to get the coax cable into my cab with out going through the weather stripping or drilling anything. does anyone have any tips that may help?:)
     
  20. rizzjc

    rizzjc Scubajoe - Radio Mod Staff Member Moderator Elite Explorer

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    You might get more responses if you post a new thread on this, instead of having it hiding here in a sticky about antenna operation, but usually you can find a grommet through the firewall that you can poke a wire through.
     
  21. LONO100

    LONO100 Well-Known Member

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    this link has pics of how i got my cb antenna into the cab of my 03 trac. i didnt drill or punch anything, and its a completely clean install. hope this helps.
     

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