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Different Look At 102" Whip Discussion

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  #9  
Old 03-05-2012, 07:41 PM
BOOTY MONSTER
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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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Old 03-05-2012, 09:03 PM
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Quote:
Originally Posted by BOOTY MONSTER View Post
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 .
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?
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Old 03-05-2012, 09:09 PM
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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:

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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Old 03-05-2012, 10:04 PM
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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....
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Old 03-06-2012, 01:24 AM
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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.
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Old 03-07-2012, 05:06 AM
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Default Nice mounts

Really nice hand made mounts

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Old 03-07-2012, 07:50 AM
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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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Old 03-07-2012, 09:40 AM
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Quote:
Originally Posted by BOOTY MONSTER View Post
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 .
BM, do you really think a 102" whip will show a 2.5 SWR if the ground plane part of the installation is suitable? I've heard similar stories for ever, and that is why I decided to do my 1/4 wave work in the summers of 2003/2006... trying to understand what goes on with a 1/4 wave radiator.

IMO, the 10K raised coil antenna is less effected by the physical ground plane presented, or said another way, it just doesn't need as much ground plane to allow it to work effectively...as long as the coil is effective and well in the clear.

Your own experience with your homemade Starduster type ground plane should give you a clue in this regard, because I think you saw a good match. What else besides the ground plane is possible to cause such bad results in your mobile install, assuming it's installed correctly?

A 1/4 wave radiator requires a good ground plane, and what you get or think you get with a mobile in this regard...is almost always a little less than suitable.

The open coil mobile type antennas are just more forgiving with mobile installs with a poor ground plane.

Compare the match and SWR with these Eznec models below and you'll see what is likely to happen as the ground plane becomes less effective with a 1/4 wave radiator. Your mobile SWR problem probably has little to nothing to do with the radiator itself.

These three models shown are with the same radiator and the radials are:
Horizontal
Slightly slanted like a mobile might present
Slanted less than 50* degrees like your SD'r might have presented.

Bm's 102'' radiator idea..pdf
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