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Thread: Antennas...

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    prerunner1982's Avatar
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    Default Antennas...

    Over the last couple of months I have tuned/tested dozens of CB antennas for my local Jeep group and have three recommendations for new comers to the CB radio world.

    Nylon washer.... it goes on top between the mount and the antenna.

    GROUND your antenna mount. This isn't too hard on the Cherokee as most of us use a mount that bolts up around the tail lights. However, on the Wranglers/CJs they like to use tailgate/tiregate mounts. The tire carrier and tail gate do not make much if any metal to metal contact with the body resulting in high SWRs. The antenna isn't use able to use the body as a ground plane and therefore uses the next closest thing...the coax. The energy is then sent back towards the radio. Use it this way too many times and you will kill your radio. Also, you may be able to hear others, but you won't transmit worth a damn.

    The Loooooonger the better. Or the more above the roofline the better. If you are going to run a supershort antenna (3') mount it on the top of the vehicle. If you are going to mount the antenna by the tail light, get at least a 4', but a 5' would be better. You have to park in the garage you say? Get a quick release or fold over adapter or tie the sucker over...The adapter itself is a compromise but would likely be better than a short antenna. For most casual CB users, its all a compromise.
    I was working on one guys TJ... everything was grounded and clean and still high SWRs.. I put my 102" whip on his mount and SWR was 1.2:1. He was running a 3' antenna... he swapped it out for a 4' antenna and the SWR got better... not great but better. I have since run into this many more times.... It's a worse problem with Wranglers because they can't mount them on top, but at that point a short antenna on a fender lip mount would likely be better than back by the tail light or on the spare tire carrier. At least on the front, it is above some sort of ground plane.

    This has been a Public Service Announcement.... I will now return you to your regularly scheduled programming.
    Last edited by prerunner1982; 01-13-2014 at 10:35 PM.
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    Default Re: Antennas...

    Man, these things always come on during the show... WHY NOT ON THE COMMERCIALS! Sheesh!!!










    Nice info bud.

    Sent via messenger pigeon - i talk, he types.

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    Default Re: Antennas...

    If I remember correctly 18 feet of coax is the ideal length for a cb antenna.

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    Default Re: Antennas...

    Quote Originally Posted by xj-jake View Post
    If I remember correctly 18 feet of coax is the ideal length for a cb antenna.
    The shortest length needed is the ideal length.

    If we took the same "theory" that 1/2 wavelength of coax is the ideal length and applied it to a different frequency... say 40 meters (7Mhz) (Amateur radio), then I would need to have 70' of coax in my Jeep..... or how about 70 cm (440Mhz), I could only run 1.1 feet of coax between my radio and antenna. Neither of those seem very logical/practical.

    If anyone tells you that your SWRs won't read right if you don't use 18' of coax....they are wrong. The coax just carries the signal... the SWR is at the antenna not the coax.
    Last edited by prerunner1982; 01-14-2014 at 08:07 PM.
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    Default Re: Antennas...

    If I remember correctly the reason for 18ft of coax, is a full wave is 72ft.18ft goes into 72ft 4 times or a 1/4 wave, most antennas are 1/4 wave antenna's so your now at a 1/2 wave. The CB itself will account for aprox a 1/2 wave so your now very close to a full wave therefor allowing for a better match. So antenna length and coax length DO make a huge difference in getting a correct match. Oh and you never want to coil excess coax or loop it over itself , although it is insulated EMP will occur and effect the SWR.


    Here's some trivia for ya ever seen the radio towers painted red and white?? Each colored section is 72ft and reflects the wave strength of the tower.
    Last edited by xj4life2; 01-15-2014 at 01:28 PM.
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    Default Re: Antennas...

    Quote Originally Posted by xj4life2 View Post
    If I remember correctly the reason for 18ft of coax, is a full wave is 72ft.18ft goes into 72ft 4 times or a 1/4 wave, most antennas are 1/4 wave antenna's so your now at a 1/2 wave. The CB itself will account for aprox a 1/2 wave so your now very close to a full wave therefor allowing for a better match. So antenna length and coax length DO make a huge difference in getting a correct match. Oh and you never want to coil excess coax or loop it over itself , although it is insulated EMP will occur and effect the SWR.


    Here's some trivia for ya ever seen the radio towers painted red and white?? Each colored section is 72ft and reflects the wave strength of the tower.
    If I can't coil the coax what am I supposed to do with 70' of it?

    The coax is not a radiating part of the antenna, therefore it having to be 1/2 wave length is not relevant. If the coax is part of radiating element, your system isn't set up correctly. Also the signal running through the coax moves slower than the speed of light, it's called the Velocity factor (VF). This means that the wavelength would actually be shorter. RG 58 (typical CB coax) has a VF of .66. 18' x .66 = 11.8'

    So really calculating for the loss in speed of the signal an 18' coax wouldn't do any better for the "system" than a 5' coax since it is 50% longer than needed.... this really doesn't matter either.

    As long as the feeling impedance matches the feedpoint impedance... the length of the coax doesn't matter.
    Last edited by prerunner1982; 01-14-2014 at 08:07 PM.
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    Default Re: Antennas...

    Quote Originally Posted by xj4life2 View Post
    Here's some trivia for ya ever seen the radio towers painted red and white?? Each colored section is 72ft and reflects the wave strength of the tower.
    It's actually advised by the FAA and required by the FCC.

    Colors are Aviation Orange and White and alternating to providing maximum visibility by contrast in colors. Required for towers over 200 ft. (not related to strength of tower....)

    Color Band Characteristics.

    1. Equal in width, provided each band is not less
    than 1 1/2 feet (0.5m) or more than 100 feet (31m)
    wide.
    2. Perpendicular to the vertical axis with the
    bands at the top and bottom ends colored orange.
    3. An odd number of bands on the structure.
    4. Approximately one-seventh the height if the
    structure is 700 feet (214m) AGL or less. For each
    additional 200 feet (61m) or fraction thereof, add one
    (1) additional orange and one (1) additional white
    band.
    5. Equal and in proportion to the structure’s
    height AGL.

    there is also a height to bandwidth (width of paint band, not radio related) ratio.
    Attached Thumbnails Attached Thumbnails Height to bandwidth ratio.JPG  
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    Default Re: Antennas...

    Also using a similar theory (specific freq requires a specific length coax) ........

    A specific PSI would require a specific length hose...

    And...

    A specific Amperage would require a specific length of wire.
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    Default Re: Antennas...

    Um... Why not just a ham radio license and enjoy Reliable communications?
    I have been a ham for over 20 years, HF (Low Frequencies like 27Mhz) on a vehicle are seldom better than a bad compromise. It is nearly impossible to get a balanced antenna.
    On my bike, I run 2m/70cm, APRS and can track my friends real-time on my Garmin 2006C.

    As for the coax length, it can be used for a counterpoise (Ground plane) but if you ground the coax to the antenna mount and thus the body of the vehicle and you ground the radio to a nearby body ground you just created a dual uneven ground return that can induce some pretty weird noise issues on stereo/CB.

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    Default Re: Antennas...

    Quote Originally Posted by OldFaurt View Post
    Um... Why not just a ham radio license and enjoy Reliable communication?
    Agreed, but not every Jeeper wants ham radio. So just passing on info to help them.
    Last edited by prerunner1982; 01-15-2014 at 11:06 AM.
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    Default Re: Antennas...

    ok fellas this is what I was asking about the other day.

    so... ham radios can only talk with other hams. but have 15x the power?
    http://www.gigaparts.com/Product-Lin...FUgS7AodlkIA3A

    and are useless in communicating with CB's?
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    Default Re: Antennas...

    from another board:

    CB, and HAM complement each other.

    CB will get you more and better road info faster, but you have to put up with the Potty mouthed goons. CB will get you comms with your non-HAM neighbors. (assuming you want that)
    UPSIDES: No license required, low entry cost on hardware.
    DOWNSIDES: limited bands (one 11 meters) and only 40 frequencies, and only Voice mode, but Single Side band helps. Limit of 4 watts PEP. Virtually unregulated, any jerk can get on the air, many using several times the legal limit on power, intell quality is low for almost everything except road conditions.

    HAM will get you more and better info on local (you county) conditions; especially in an emergency (severe weather, wildfires, floods, ect) because most local HAM clubs are well tied into the local emergency management systems. (EMS, Sheriff's Office, Local PD ect.)
    UPSIDES: Well regulated, and regulations are policed by the community of HAMS themselves. Basic license allows voice operation on 23cms, 33cms, 70cms, 1.25m, 2m, 6m, and ssb voice on part of 10m. Not all but most bands and modes allow up to 1500 watts PEP. A 2m radio with access to a well positioned local repeater will give you communications ranges in excess of 30 miles. With a General class license, you have world wide communications capability. A General class license, gives you access to all HAM bands, and over 90% of the frequencies available. (if you have the hardware) The Amateur Radio community has a lot of expertise, and is more than willing to share it. MORSE CODE IS NO LONGER REQUIRED FOR ANY HAM LICENSE.
    DOWNSIDES: License required(but you can be ready for a Tech test in as little as a week if you work at it, and the General license is just as easy) Equipment generally costs more, but is of better quality.


    My recommendation is: if all you want is road info, go with CB, but if you are looking to have general communications capability, then you need to do both. You can get started in HAM on 2m (that's where almost all the local action is) for less that 500. (license, radio,antenna and all).
    Read more at http://www.survivalistboards.com/sho...OeYcmPmIC1B.99
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    Default Re: Antennas...

    "Most modern multiband hams can broadcast on 11M (CB)" true??
    Wheelin' East Texas in a RED XJ

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    //___l__,\____\,00_
    l_--- \___l---[]lllllll[]|
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    Default Re: Antennas...

    Quote Originally Posted by denverd1 View Post
    "Most modern multiband hams can broadcast on 11M (CB)" true??
    There are ham radios that can.... but it is not legal for a ham radio operator to use his ham radio on 11 meters (CB).
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    Default Re: Antennas...

    Quote Originally Posted by prerunner1982 View Post
    Over the last couple of months I have tuned/tested dozens of CB antennas for my local Jeep group and have three recommendations for new comers to the CB radio world.

    Nylon washer.... it goes on top between the mount and the antenna.

    GROUND your antenna mount. This isn't too hard on the Cherokee as most of us use a mount that bolts up around the tail lights. However, on the Wranglers/CJs they like to use tailgate/tiregate mounts. The tire carrier and tail gate do not make much if any metal to metal contact with the body resulting in high SWRs. The antenna isn't use able to use the body as a ground plane and therefore uses the next closest thing...the coax. The energy is then sent back towards the radio. Use it this way too many times and you will kill your radio. Also, you may be able to hear others, but you won't transmit worth a damn.

    The Loooooonger the better. Or the more above the roofline the better. If you are going to run a supershort antenna (3') mount it on the top of the vehicle. If you are going to mount the antenna by the tail light, get at least a 4', but a 5' would be better. You have to park in the garage you say? Get a quick release or fold over adapter or tie the sucker over...The adapter itself is a compromise but would likely be better than a short antenna. For most casual CB users, its all a compromise.
    I was working on one guys TJ... everything was grounded and clean and still high SWRs.. I put my 102" whip on his mount and SWR was 1.2:1. He was running a 3' antenna... he swapped it out for a 4' antenna and the SWR got better... not great but better. I have since run into this many more times.... It's a worse problem with Wranglers because they can't mount them on top, but at that point a short antenna on a fender lip mount would likely be better than back by the tail light or on the spare tire carrier. At least on the front, it is above some sort of ground plane.

    This has been a Public Service Announcement.... I will now return you to your regularly scheduled programming.
    {cough}CB segment!{cough}

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