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Different Look At 102" Whip Discussion

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Old 03-05-2012, 09:56 AM
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Exclamation Different Look At 102" Whip Discussion


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.


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Old 03-05-2012, 10:14 AM
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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

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Old 03-05-2012, 10:54 AM
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Isn't 1/4 @ 108"? Adding the 6" spring would bring it up to 108" right?
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Old 03-05-2012, 11:27 AM
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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 .

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Old 03-05-2012, 12:29 PM
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Quote:
Originally Posted by 15minigrass View Post
Isn't 1/4 @ 108"? Adding the 6" spring would bring it up to 108" right?

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"

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Old 03-05-2012, 06:31 PM
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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.

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Old 03-05-2012, 06:44 PM
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A CB Classic!! Heavy Duty 3 1/2" Mounting Plate with Ball Mount. Comes with 6" HD Chrome Plated Barrel Spring. Standard 3/8"x24 Mounting Threads Accept Virtually all Standard Type CB Antennas. Accepts Spade Style Coax Connections. Per
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Old 03-05-2012, 06:48 PM
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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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