102 inch antenna

[RatsoW8]

I divided 11 meters by 4, which gave me 2.75 meters. I then went to Google, and had Google convert 2.75 meters into a measurement in inches. The result was 108.2677 inches.

I suppose that, since I am most frequently on Channel 19, I could tailor the antenna to that specific frequency, but would the effort be worth the reward? (<~~ Actual question, by the way; not being sarcastic )

492/f is correct for calculating the 1/2 wave length of an antanns in free space but since our signals travel througth wire or other solid metal like a whip we use 468/f to build antennas. I supose the same theory applies to 1/4 verticals as well.

I suppose if you use a superconductor for the radiator 492/f would work. I'm no engineer but that how I've been building antennas for the last 30 years and it seems to work.

 

[Sarasota Slim]

492/f is correct for calculating the 1/2 wave length of an antanns in free space but since our signals travel througth wire or other solid metal like a whip we use 468/f to build antennas. I supose the same theory applies to 1/4 verticals as well.

I suppose if you use a superconductor for the radiator 492/f would work. I'm no engineer but that how I've been building antennas for the last 30 years and it seems to work.

I'm no engineer, either, lol. I'm also not educated enough to understand the reasoning behind either the 492/F formula, or the 468/F formula. I'm still pretty new to this stuff. I'm pretty sure that I have an explanation of it in my antenna book; I just probably haven't gotten that far into it, yet. I just got the book.

I see where you got your measurement of 103.3", though.

I love to tinker, and mess around with things, so I reckon that I'll try different lengths, and see what performs the best

 

[fourstringburn]

Those 492/F formulas are shortcut methods. The more scientific formula which will give a better understanding of what the numbers mean should be learned first.

Wavelength equals speed divided by frequency. 300 / Freq. = Wavelength in meters

The speed of a radio wave is 300 million meters per second in free space.

So divide 300 (no need for the extra zeros) by 27.185 MHz and that comes to 11.035 meters and that's the full wave length at that frequency. In case you didn't know that's why the CB band is known as the 11 meter band.

Convert meters to feet for us Americans by multiplying 11.035 or 11 by 3.28 and you get 36.2 ft for a full wavelength . You can shortcut by multiplying 5.5 for 1/2 wave or 2.75 for 1/4 wave.

If you make a 1/2 wave 11 meter dipole at 18 ft to start with, then the velocity factor will come into play and the antenna length would probably be shortened some for better tuning. At least this way you will know your antenna wire length will be long enough to start with.

Velocity factor is the difference between a radio wave traveling thru free space or a vacuum and a transmission line which is slower but only by a fraction.

 

[Pamm r]

I installed mine this weekend, No swr, woo woo......

 

[undertaker]

with the 6 inch spring mine is almost flat...

 

[fourstringburn]

A 102 whip should measure about 37 ohms on a typical mobile install. This should read an SWR value around 1.8. if measured with a good antenna analyzer and a short jumper.

As long as you like what you see on your meters, you're good to go.

 

[undertaker]

Those are the numbers my MFJ analyzer tells me

 

[fourstringburn]

Those are the numbers my MFJ analyzer tells me

Showing 50 to 52 ohms without any antenna modifying?

 

[undertaker]

Yes sir!!! guess im just lucky.. I have always had good luck with the whip on my tool box..

 

[fourstringburn]

Yes sir!!! guess im just lucky.. I have always had good luck with the whip on my tool box..

Interesting…

 

[undertaker]

Now I am using the ring and terminal coax. When I used the other type my swr was way off. Not sure if it is the coax or not. But it does work ..

 

[Global mobile]

Interesting…

That is interesting to have 50 ohms with a 102 inch. Did he say he was using the spring ? With the whip on my roof I show an SWR 1.8 and around 37 ohms..

 

[fourstringburn]

That is interesting to have 50 ohms with a 102 inch. Did he say he was using the spring ? With the whip on my roof I show an SWR 1.8 and around 37 ohms..

Welcome to the Forum!

He must have used an antiquated MFJ-259 analyzer. Even MFJ has a new line of modernized analyzers to try to compete with all the new digital ones today.

I like my RigExpert AA54. This far exceeds the 259's in quality, features, and accuracy and only uses 2 AA batteries as opposed to the MFJ using 10 and eats them up quick.

 

[Pamm r]

Ok, New area for my 102" whip. On the rear bumper corner on my pickup it has great low swr 1.1

But I want to move it to the center of my alum toolbox . When installed to the lower center it looked great but swr was 2.5 Grounds are all good. Is it because the antenna is mounted so low down in the bed of the pickup?

 

[undertaker]

Mine is mounted on the back center of my tool box