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Different Look At 102" Whip Discussion

Discussion in 'CB Antennas' started by Wire Weasel, Mar 5, 2012.

  1. Wire Weasel

    Wire Weasel Senior Moment

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    The following doesn't always get brought up in discussions of the venerable 102" stainless steel whip for use as a high reliability, broad-banded, good working antenna for 10-11-12 meters.

    Very common for CB. This antenna will be a full 1/4 wave ground plane.

    What is commonly found on many vehicle installations is that you put this whip on by itself and find find that the SWR is not flat in the CB area, say in the middle at channel 20.

    Common to find again that with testing it is discovered that the center resonance point is further up the band. The math will show that the center resonance point on 102" is right about at 27.520 mhz or "Channel 52" for you sophisticated raydideo operators. Checkout and save the 1/4 ground plane calculator below.

    Amateur Quarter Wave Ground Plane Antenna Calculator


    So why is this? Why do they make and market the 102" whip as a ready-for-CB antenna when actually it is not ready for CB (many installations) and has to be lengthened to be resonant square in the CB band, commonly accomplished by adding a 4 inch heavy barrel spring, or by using a solid Shaft Extender?

    I don't know. I just know that on my pickup and every vehicle I have ever run one on, and as most of the locals around here find....you must do something to lengthen the 102 to make it flat line the SWRs in the CB band....which is critical when running an amplifier....which is always best run with no or very little SWR.

    This is a good lesson for newbies in particular as one might expect to simply go to a CB antenna seller, purchase a made-for-CB antenna, slap it on the car and expect it to work with no tuning or adjustments....and particularly so for the 102 whip that appears to be complete and there isn't anything to adjust anyway.

    So most installations require the addition of the 4 inch spring which has a wire running up inside it, which effectively lengthens the whip another 4 inches.

    Even that is insufficient on some installations and even more lengthening is required. This was so on my pickup and I had to add 6 more inches to achieve at flat SWR across the CB area. I used a 6 inch Shaft Extender from Monkey Made Antennas for this.

    There is another handy solution. MFJ still makes a 108" Stainless Whip which should be just what the doctor ordered and should give excellent resonance on CB by itself. Their part number is MFJ-1966 and they are $26.95 which is a reasonable price. (Their) problem here is - because it is so long it is an oversize package for shipping and the shipping on these costs more than the antenna does....unfortunate.

    But still is less than what you would pay for something like a new Wilson 5000 magnet mount.....so cost is relative.

    Just something to think about when considering the 102

    Again it makes me wonder why all the manufacturers didn't just offer a 108" all along.




    Comments? [​IMG]
     
    #1

  2. another option for adding length that is inexpensive if you already have the 102 is to add a 5 inch wilson trucker shaft . the 10 inch K40 shaft will work also ,and so will the longer wilson shafts ..... but the stinger will need to be cut for the CB band .

    FWIU , adding a big spring under then made the 102 run lower in the air and hit less things , as well as giving the needed length
     
    #2
  3. 15minigrass

    15minigrass Active Member

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    Isn't 1/4 @ 108"? Adding the 6" spring would bring it up to 108" right?
     
    #3
  4. on my wire starduster i made the vertical 110 inches and wound up cutting about 4 inches off , maybe a little more . the ground plane will effect the final tuned length .
     
    #4
  5. Wire Weasel

    Wire Weasel Senior Moment

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    Hi Mini, Never heard of a 6" spring. The typical fat barrel spring is 4"

    I use a 6" Shaft Extender which brings mine up to 108"
     
    #5
  6. IRock817

    IRock817 Active Member

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    I remember back in the day, that rat shack made a ball mount for the 102"!
    I had the ball mount, heavy spring and flat swr!

    I think the ball mounts are still available. (y)
     
    #6
  7. Robb

    Robb Yup

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  8. IRock817

    IRock817 Active Member

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    That's the ticket!!!!
    It's adjustable too, so you can get 'er to stand at attention!!
     
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  9. http://www.dxengineering.com/Products.asp?ID={39F55488-F985-4A3A-A58B-67A6EDA81F4F}&SecID=74&DeptID=25

    stainless steel last longer than nickle plate . the copper braid is the real weak point in springs though .
     
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  10. 6.0 Liter

    6.0 Liter Coax abuse???

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    Hey Booty, just for curosity sake, that length would probably be more in the instance of a poor groundplane? With a better performing ground plane, the vertical would be a bit shorter?:pop:
     
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  11. Marconi

    Marconi Supporting Member

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    I might agree with WW regarding the 102" whip installed on a mobile, but it is not specifically a problem with the length of the whip just to be accurate. The problem with mobiles is a typical lack of a suitable ground plane for the radiator to work against.

    To demonstrate how the 102" whip can respond in SWR and resonance in the CB band with a good ground plane, I did an SWR bandwidth curve video: Marconi Demonstrates Antenna SWR Bandwidth Curve - YouTube

    The antenna in this video was my Marconi 7x made using 7 x 102" stainless steel whips. The basic setup uses a mobile mirror mount and two A99 GPK hubs for the radials attached to a mast. You will see that this 102" whip and a good ground plane works very well in the CB band.

    Marconi 02 hub of antenna (640x480).jpg

    Just as a note: I made a small math error in determining the total bandwidth for this antenna, so forgive me.

    6.0 Liter is right on point too.
     
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    Last edited: Mar 6, 2012
  12. ThirstyBoots440

    ThirstyBoots440 Local Trash Talker

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    Of course I used to run a 102" whip on my mobile, and had a completely adjustable rig thanks to a "Gunslinger" whip adjuster. Why doesn't someone offer a 108" whip? I believe MFJ does if I'm not mistaken....
     
    #12
  13. W5LZ

    W5LZ Crotchety Old Bastard

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    If the length of an antenna is determined by how good the SWR is, then you are not considering resonance at all, which is what determines how well an antenna works. SWR only tells you about the impedance match of the antenna system, nothing else. Tuning an antenna consists of two things, making it resonant and matching impedance. An SWR meter can tell you absolutely nothing about resonance.
    - 'Doc
     
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  14. Blackpaw

    Blackpaw Member

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    #14
  15. most of us CB'er only have a vswr meter for checking/tuning antennas . folks have been getting by with just that for decades . using a analyzer could do a better job though . on my mobile my 10k tunes to 1.3 on a mfj259b at the shop , but take it off and put on a 102 whip and it shoots above 2.5 .
    resonance smesonance ....... i refuse to try to run a radio into that kind of vswr , so i stuck with the 10k .
     
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