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Thread: Antennas...

  1. #16
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    Default Re: Antennas...

    Quote Originally Posted by Mudderoy View Post
    {cough}CB segment!{cough}




    Typical HAM attitude to the poorer cousins ..


    Poor ol 27mhz .... It died in the arse years ago down here ... Got replaced by useless short range UHF.

    Was a lot of fun tho ..
    I hate watching simplicity and reliability being ruined by bureaucracy and technology.

    Quote Originally Posted by MattybPDX
    If my jeep is going to be a grocery getter it's at least going to be a friggin awesome one.

  2. #17
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    Default Re: Antennas...

    Quote Originally Posted by Carves View Post



    Typical HAM attitude to the poorer cousins ..


    Poor ol 27mhz .... It died in the arse years ago down here ... Got replaced by useless short range UHF.

    Was a lot of fun tho ..
    CB came out before technology was ready. The creators of CB always wanted it for short public communication.

    And the CB segment comment was my way of telling Prerunner he should think about recording a CB Radio segment for the XJ TALK SHOW! 5 minutes and tell people things like he's telling them here.

  3. #18
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    Default Re: Antennas...

    Quote Originally Posted by Mudderoy View Post
    .... And the CB segment comment was my way of telling Prerunner he should think about recording a CB Radio segment for the XJ TALK SHOW! 5 minutes and tell people things like he's telling them here.
    ahhhh .. ..

    Get him to work then ... as that sounds like a good idea ..
    I hate watching simplicity and reliability being ruined by bureaucracy and technology.

    Quote Originally Posted by MattybPDX
    If my jeep is going to be a grocery getter it's at least going to be a friggin awesome one.

  4. #19
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    Default Re: Antennas...

    yea, this newbie would like to understand it more.

    BTW I bought this: [ame="http://www.amazon.com/Uniden-40-Channel-CB-Radio-PRO505XL/dp/B005ZLB0E4/ref=sr_1_26?s=electronics&ie=UTF8&qid=1389885222&s r=1-26&keywords=uniden+bearcat"]Amazon.com: Uniden 40-Channel CB Radio (PRO505XL): Electronics@@AMEPARAM@@http://ecx.images-amazon.com/images/I/41efmMTI5UL.@@AMEPARAM@@41efmMTI5UL[/ame]

    and I need an antenna apparently. Anyone care to make a recommendation? and the corresponding coax length? Just a "trail unit" at this point, but would like the longest (reasonable) communication distance I can get.
    Last edited by denverd1; 01-16-2014 at 10:14 AM.
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  5. #20
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    Default Re: Antennas...

    Quote Originally Posted by denverd1 View Post
    yea, this newbie would like to understand it more.

    BTW I bought this: Amazon.com: Uniden 40-Channel CB Radio (PRO505XL): Electronics

    and I need an antenna apparently. Anyone care to make a recommendation? and the corresponding coax length? Just a "trail unit" at this point, but would like the longest (reasonable) communication distance I can get.
    I would suggest the longest antenna you can live with, if you have to park in a garage and the antenna won't clear I would consider a quick disconnect or a fold over mount rather than a physically shorter antenna. Neither is a great option. If you run a 102" whip, you can bend it over and tie it down like Tony has his. The 102" is the best antenna for the job however if you travel wooded trails the whip will "whip" around a lot if not tied down.. A 5' Firestik II would clear the vehicle enough to give reasonable communication....but it won't beat the 102" for overall performance/distance.

    Coax length... it whatever gets the job done. 4' 5' 18'... whatever it takes to go from the antenna mount to the radio with a little slack.

    With an older version of the radio you have and a 102" whip I can get 10 miles out in the flat country (few obstructions) with about 2 watts (what my watt meter says my radio is putting out). Radios say they put out 4 watts (legal limit), but would be surprised if any are actually real close to 4 watts. Likely closer to 3.

    In most conditions you should expect 2-3 miles of communication, though this depends on what environment/terrain/surroundings you are in.
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  6. #21
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    Default Re: Antennas...

    Quote Originally Posted by Carves View Post



    Typical HAM attitude to the poorer cousins ..


    Poor ol 27mhz .... It died in the arse years ago down here ... Got replaced by useless short range UHF.

    Was a lot of fun tho ..
    Well, do remember that a lot of HID headlamps operate in the 27Mhz range! that is what I call noise that lights you up!
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  7. #22
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    Default Re: Antennas...

    Found an ONLINE coax length calculator! Makes it easy to know what length coax you need for each installation!

    Works for fixed or mobile installations!

    http://www.angelfire.com/electronic/...alculator.html

  8. #23
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    Default Antennas...

    Coax length comes into play. You can actually tune and or notch frequencies using specific lengths of coax. The 18 ft thing only apples to the non-tunable 108" whips, otherwise you match the antenna to the coax length when you tune it.

    Even 1/4 wave of coax (accounting for velocity factor) is a perfect 50 ohm match where odd quarters are more resistive.

    Once upon a time Motorola built a diplexing chart for one of their low band radio lines which could allow for diplexed antennas using nothing more than specific lengths of coax and a T connector.

    Also co-phasing requires an odd quarters of 75 ohm cable to be teed together and then simply attached to a 50 ohm piece to the radio.


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    Last edited by xjzaped; 09-26-2016 at 01:17 AM.

  9. #24
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    Default Re: Antennas...

    Quote Originally Posted by xjzaped View Post
    Coax length comes into play. You can actually tune and or notch frequencies using specific lengths of coax. The 18 ft thing only apples to the non-tunable 108" whips, otherwise you match the antenna to the coax length when you tune it.

    Even 1/4 wave of coax (accounting for velocity factor) is a perfect 50 ohm match where odd quarters are more resistive.

    Once upon a time Motorola built a diplexing chart for one of their low band radio lines which could allow for diplexed antennas using nothing more than specific lengths of coax and a T connector.

    Also co-phasing requires an odd quarters of 75 ohm cable to be teed together and then simply attached to a 50 ohm piece to the radio.


    Sent from my iPhone using Tapatalk
    I think the length of the feed line only comes into play if you are not connecting to an antenna that isn't the same resistance as the feedline. If the radio, feed line and antenna are all 50 ohms then the length of the feedline shouldn't matter.

  10. #25
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    Default Re: Antennas...

    Quote Originally Posted by Mudderoy View Post
    I think the length of the feed line only comes into play if you are not connecting to an antenna that isn't the same resistance as the feedline. If the radio, feed line and antenna are all 50 ohms then the length of the feedline shouldn't matter.


    It does…98% of mobile installs you tune the antenna to match the system (antenna, feed line, radio) because it's easy to access.

    About 6 months ago I was managing an antenna replacement job for a MSS. They went to test the new antenna and kept getting high (2.1:1) SWR. The tech had placed his meter between the jumper coming off the duplexer and the 7/8" coming out of the poly phaser. The jumper was 1/4 wave long. I told him to put an additional jumper (quarter wave) in front of the meter to see what the duplexer is actually seeing. SWR dropped to 1.4:1. Also the reason jumper length between cavity filters are critical.


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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.
    Thank you, I have my nylon washer on the wrong side of the bracket, that probably explains why my SWR won't go below 3.

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