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Different Look At 102" Whip Discussion

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  #25  
Old 03-09-2012, 09:26 AM
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234 / f (in Mhz) = feet

234/27.205=8.6 feet

102/12"=8.5 feet

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  #26  
Old 03-09-2012, 09:30 AM
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Originally Posted by Happy_Hamer View Post
Maybe I am wrong, but I thought in the past I bought a 102 inch antenna from the rat and just for the hell of it I measured it and it was only 96 inches, I went back to the rat and he said technically it is supposed to be mounted with the 6 inch coil to equal 102?

RS used to sell more ham gear including 10 meter mobiles and associated supplies. I also remember their offering a 96" whip and that clearly was for 10 meters.

I have still never seen a 6" coil spring anywhere excepted for some big tough military piece.

W5LZ and some of the others are correct also with the many comments regarding satisfactory grounding and placement issues. Every installation is going to be different and one will have to just "see what works" on any particular vehicle and antenna arrangement.

Power output is also going to be a factor , especially with adequate grounding issues. A setup that appears to work well with 4~100 watts power may see the SWR go off the chart if you try to slap some big 8 pill monster in there.

You just have try things and see what works out on each and every installation and do what is electrically necessary to make everything happy.

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Old 03-09-2012, 10:50 AM
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gamegetter,
Right, and that 0.1 foot is 1" and a little bit. So, 102" + 1" = 103", not 108" or whatever. The only 1" mount I've ever seen was one of the 'acorn'/'beehive' things. Most of those I would have doubts about holding a 102" whip, so if using a bigger/taller mount, then I'd cut that 102" whip down a bit to get it to the 'right' length. Does that mean it'd have a real nice SWR? Nope, but I'd bet it would be within reason.
- 'Doc

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Old 03-09-2012, 10:53 AM
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folks get hung up with swr and try to match by cutting the antenna and throwing resonance off.
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Old 03-10-2012, 02:54 AM
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[QUOTE=maddog355;355416]When I had mine mounted on the rollbar the needle never moved when I would check the SWR, Someone told me that SWR being too low was a bad thing so I went to 12' of coax and that got them to 1.3. As for drive throughs, My truck is not drive through friendly anyway.[/QUOte

How can SWR be too low? CB stands for Continuous Bullshitting.
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Old 03-10-2012, 05:09 AM
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The idea, not having the SWR get too low, was a justification for not wanting too good of a signal so that you would be under suspicion of doing something wrong. Sort of like, where did you get all that money you're spending unless you robber a bank, you know? It really doesn't work that way.
- 'Doc

(unless you happen to be a bank robber)

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  #31  
Old 03-10-2012, 09:18 AM
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I do not post much on 1/4 wave threads because I often get myself in trouble with this topic because of my choice of words, but....


Posted By WW:
Quote:
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.
Posted By BM:
Quote:
the ground plane will effect the final tuned length .
Posted by 6 Liter :
Quote:
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?

Posted by Marconi:
Quote:
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.
Quote:
You will see that this 102" whip and a good ground plane works very well in the CB band.
Posted By DOC :
Quote:
SWR only tells you about the impedance match of the antenna system,
Posted By BM:
Quote:
but take it off and put on a 102 whip and it shoots above 2.5 .
Posted By Marconi :

Quote:
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.
Posted By Gamegetter:
Quote:
my 102's have always matched well, always 1.5 to 1 or less.
I would Keep going, But there seems to be a pattern here.

This Post I agree with 100%

Posted By gamegetter.:
Quote:
folks get hung up with swr and try to match by cutting the antenna and throwing resonance off.
I know the example I am about to talk about is a Base antenna, but just to think about, ....the I10-K is tuned by setting the length of the antenna and THEN adjusting the trombone for best bandwidth/SWR.
( then re-read the above and take out the word trombone and insert the words feed-point for just a second)

Now Back to this:
Amateur Quarter Wave Ground Plane Antenna Calculator
The numbers are there, no mater how many times you try it.

And what DOC is saying about
""just because it shows good SWR don`t mean that the antenna is resonate""
many antennas can be the correct length, but exhibit SWR that is real bad, because of several factors.
Design
Feed
Location
Lack of Good Ground plane ( iF the design needs one)

Then Look at this Image From The K0BG. com web site.




many Guy`s, look at that and go...
W T F ?
That is BS....How can that work ??? You just shorted the Coax to ground!!!
That is a dead short!

I will finish...
An antenna Can show Good SWR and yet NOT be the correct Length.
An Antenna CAN be the correct Length and show BAD SWR.
This is why we need to MATCH the feed point of the antenna.
regardless of the SIMPLE idea of a 1/4 wave mobile set-up, it can often be complicated because there are so many factors that are different in a mobile mounting set-up.

RF is a Strange thing, Well...No RF is a Complex thing......
R= X= Ohms.......
SWR is but one thing in the whole picture, and in most cases it will get you by, because as long as you radio is happy with what it see`s at the coax connector on the back of the radio, it has that warm fuzzy everything is good feeling.
And "most" of the time that works well.
73
Jeff
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  #32  
Old 06-04-2013, 12:40 PM
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Quote:
Originally Posted by AudioShockwav View Post

Then Look at this Image From The K0BG. com web site.




many Guy`s, look at that and go...
W T F ?
That is BS....How can that work ??? You just shorted the Coax to ground!!!
That is a dead short!
73
Jeff

also notice the size/ diameter of the coil,.... the diameter is the same as the length, also called a "1x1" coil....... guess what happens when some golden screwdriver streaches the coil
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