quick and dirty cb antenna

Discussion in 'General Electronics Chat' started by lokeycmos, Jul 18, 2011.

  1. lokeycmos

    Thread Starter Active Member

    Apr 3, 2009
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    so i pulled a Cobra 18 WX ST II out of the dumpster. had a bad diode causing a short on the input. got that fixed. anyone have an idea for a quick and dirty antenna? i live in an apartment so im limited in space. im not looking for anything fancy, mostly just for testing. not planning on doing any transmitting, just want to scan and listen in on the 10 weather channels. thank you!
     
  2. Wendy

    Moderator

    Mar 24, 2008
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    Do you have a SWR meter? This is a critical piece of equipment as far as it goes. It will keep you from burning up your CB transmitter among other things.

    When the CB craze was at its most intense during the late 70s I rigged a quick and dirty antenna with a SWR meter, a 50 ohm resistor and a coat hanger.

    Before that experimenting as a teen I used to make a lot of crystal oscillator based transmitters. Since the band was designed for high power I figured they couldn't track me down among all the major cheaters and linear amps, I just wanted to get on the air. It was wild wild west days.
     
  3. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    Go to radio shack. They still sell these(most stores) for about 20-30 dollars. The antenna will be base 'loaded', meaning it will be properly configured to present a 50 ohm load to the CB. Doing something homebrewed, without proper meters and coax will result in poor reception and could fry the output section if the transmitter is activated.
     
  4. pistnbroke

    Member

    May 9, 2011
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    If you only want to listen any length of wire will do ..if you can make it about 0.8 x 1/4 of a wavelength so much the better and hang it upright.
     
  5. lokeycmos

    Thread Starter Active Member

    Apr 3, 2009
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    .8 x .25 x 27.185mhz = 7.25'

    im planning on hanging it off my 3rd floor balcony. im goona use coax to the CB. what kind of ground goes on either end of the coax? im guessing the braid will connect to the thread part of where a real antenna goes. what about the other end? im only using this for recieving. TY
     
  6. SgtWookie

    Expert

    Jul 17, 2007
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    A 1/4 wave antenna centered around channel 19 would be 9 feet and 3/4 inches long. For the best reception and impedance match, you'll need a ground plane - but that'll be tough to do hanging from an apartment window.

    RG-58U is 50 Ohm impedance, which is what's used for most transceivers. Don't use TV cable, as that's 75 Ohms impedance.

    At various times, I had a 9' fiberglass whip and a 9' stainless steel whip on a bumper mount on my car at the time. Parking ramps ended that for me. :rolleyes:

    Don't key the mic without checking the VSWR unless you want to fry the transmitter.
    Your neighbors won't like you much if you transmit in the apt.
     
  7. lokeycmos

    Thread Starter Active Member

    Apr 3, 2009
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    this is the coax i have. its considerably bigger than the coax they put in the box with a new vcr. however there is no writing at all on it to identify. how critcal is a ground? thats the part im confused on. remember its only for recieving.
     
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  8. radiohead

    Active Member

    May 28, 2009
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    that looks like RG-6. It's 75Ω. If you are receiving only, you can use just about any whip antenna, although a dual band 50 antenna would be preferred. Also, try to get some RG-58-series or RG-174 coaxial cable.

    I agree with the others' comments regarding VSWR and the use of an SWR meter. You might be able to find one at a flea market for around $10.00
     
  9. bertus

    Administrator

    Apr 5, 2008
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  10. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    There once was an Aussy electronics parts and kits house who's ads boasted the lowest price replacement antenna on the market.

    They called it the "Co-tanger."

    (say it out loud fast)
     
  11. lokeycmos

    Thread Starter Active Member

    Apr 3, 2009
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    i was able to pickup 4 channels by hanging a 9' piece of wire off my balcony, but they were very weak and couldnt make them out
     
  12. gootee

    Senior Member

    Apr 24, 2007
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    Try another 9' connected to the ground braid.
     
  13. lokeycmos

    Thread Starter Active Member

    Apr 3, 2009
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    im assuming it the opposite direction? does it matter if it is vertical or horizontal?
     
  14. Wendy

    Moderator

    Mar 24, 2008
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    Most CB antennas are vertically polarized. The direction of the antenna matters.
     
  15. gootee

    Senior Member

    Apr 24, 2007
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    The ground part should probably be oriented at least 90 degrees from the antenna part, i.e. somewhere in "the opposite hemisphere".

    Ideally, I think, you'd want the antenna portion (i.e. the coax center-connected wire) to have its unconnected end directly above where it connects to the end of the coax, i.e. vertically oriented (vertically polarized), to match everyone else's polarization, or else you will lose a lot of overall gain from not matching that.

    The "ground" part could be configured several different ways. If you let it be just one wire, you could experiment with its orientation (horizontal, vertical downward, or angled downward, at different azimuth angles, or maybe even a sort-of horizontal circle, etc). But it might be better to connect more than one wire there and array them horizontally outward like an asterisk, or probably even better: arrayed outward similarly but angled downward. Not sure if you could use 1/2 the length for those or not. Something stiffer might be easier to position how you want it.
     
  16. radiohead

    Active Member

    May 28, 2009
    474
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    Read this attachment for a basic understanding on how radio waves propagate.

    Also, get yourself an American Radio Relay League (ARRL) Antenna Handbook, and/or an ARRL Handbook for Radio Communications. These two books will serve you very well.

    http://www.arrl.org/arrl-store
     
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