beware......im trying to think again !!

[BOOTY MONSTER]

a lot (but not all) people say a 102 inch is the antenna to beat or at least match on a mobile . the draw backs are the height for some , and the ammount of bend and sway when moving . what if you had a straight shaft (like a 10k-coily-MM) all metal with no plascic spacers and no coils but say 3 or 4 or even 5 foot long with a stinger making up the additional length/height .the stinger wouldnt bend or sway any more that a wilson 500 stinger on the 3 ft base and similar to a coil antenna stinger on the 4 and 5 foot base .

this wouldnt help with height problems but it would greatly reduce the bending and swaying that a regular 102 does when driving and affecting rx and tx .it would still give a few to several feet of stinger to cushion or deflect from impact due to the height .

with the higher wind load,weight and height of the bigger base you would have to use a ball mount or a sawblade/plate mount support.

am i making any sense or just got too much time on my hands ? lol :stupid

 

[Master Chief]

It would perform just fine and you would also learn the valuable lesson that the larger diameter bottom section will make the overall height of the antenna less than 102".

The next question would be, "Will it work better than a P-10K and if it doesn't, why bother?"

 

[Seminoles]

Two much time on your hands like myself, but then I run a 8' 1/2" diameter c o p p e r/silver plated rod with a brass screw for adjustment

 

[BOOTY MONSTER]

It would perform just fine and you would also learn the valuable lesson that the larger diameter bottom section will make the overall height of the antenna less than 102".

The next question would be, "Will it work better than a P-10K and if it doesn't, why bother?"

just so i can know for future reference . why does the diameter of the bottom section (straight with no coils) affect the total height/length of the antenna ?

i couldnt run something that tall myself cause some of my family and friends have big trees with low hanging branches and im not walking from the road (bad knees here) . i was just wondering .

Seminoles got any pics of your antenna ?

 

[Master Chief]

I am going to give an exaggerated example and use round numbers to make my point. By no means are these dimensions accurate, but you will get the jist of the lesson.

Let's say we want a radiator (antenna) to be ELECTRICALLY one quarter wavelength; or in other words, "an electrical 1/4 wave length". If we use 3" diameter tubing, that electrical 1/4 wavelength may only be physically 8' long, but still an electrical 1/4 wavelength. Now let's say we want to make an electrical 1/4 wavelength out of 14ga wire. That wire may have to be physically 10' long to be an electrical 1/4 wavelength.

The difference between the 3" tube and the 14ga wire is the surface area of the conductor! The more surface area, the shorter the conductor to achive the SAME electrical wavelength!

This is really important when building antennas. The "stepping" of the elements is taken into consideration to achieve the desired electrical wavelength of the radiator (whether that be 1/4, 1/2, 5/8, .64, etc).

To illustrate this, lets take the main radiator of a 1/2 wave antenna.

Antenna 1: The first tube is 4' long at a diameter of 1". The second, third and fourth are also 4' long, but 7/8", 3/4", and 5/8" diameter respectively. The last element will be 6' long and 1/2" in diameter. When properly assembled, let's assume we have an electrical 1/2 wave antenna.

Antenna 2: The first tube is now 6' long with a diameter of 1". With the rest of the tube lengths being identical in length and size, antenna 2 will be physically SHORTER because of the extra 2' of 1" material on the first tube.

Both antennas are electrically 1/2 wavelength and perform identically (although you will see an increase in bandwidth with larger diameter antenna elements). The only difference was the surface area of the radiating element.

There is a reason the Wilson 5000 performs better than the Wilson 1000. It uses a larger diameter wire in the coil. There is also a reason why the P-10K out performs many other antennas with smaller diameter elements.

A lot of this is minuscule, but doesn't change the fact.

So, your 1/4 wave antenna with a 1/2" diameter shaft will be shorter than your standard 102" whip.

I hope I was clear enough. If not, let me know and I'll try again.

 

[W5LZ]

...Or, if you happen to have an ARRL 'Handbook' handy, skip to the antenna section start. Somewhere in there you'll run across an equation; (492 x k) / f (in Mhz) = L in feet. The '492' thingy is for a half wave. For a 1/4 wave do the half wave and divide by 2.
That 'K' refers to the diameter of the conductor that's gonna radiate. There's a graph close to this equation where you get to divide the diameter by the wave length and look the answer up on that graph. Put that 'K' in the equation and you get the length for that particular diameter conductor. For aomething the size of average wire (+/- 14ga.) the 'K' is about 0.95, which yields the 'magic' number 468, what's usually used to find the length of a dipole antenna. For 1" tubing, or 14 foot diameter tubing, do the math and look up the number in the graph. Plug it into the equation and you got it. (It'll be slightly long, but that's better than slightly too short, right?)
If you play with that 'K' number a bit on different frequencies and bands, you'll get an idea of how conductor diameter can affect lengths. The bigger the diameter the shorter the antenna. There are practical limits to that 'shortening' affect of the diameter of the conductor. I don't care how short it gets, 14 feet in diameter is kind'a unreasonable for a mobile antenna, or a fixed one, maybe...
- 'Doc

 

[4600turbo]

I am going to give an exaggerated example and use round numbers to make my point. By no means are these dimensions accurate, but you will get the jist of the lesson.

Wouldn't the 1/2 wave antenna you described is actually a 3/4 wave when taking into account the vehicle it's attached to?

Isn't the vehicle part of the antenna system. 1/4 wave part.

Just a thought.

 

[Master Chief]

No and yes.

Also, what the hell is Doc talking about?

 

[W5LZ]

'M.C.',
I'll be dipped. You really don't have an old Handbook laying around somewhere?
- 'Doc

 

[Marconi]

Antenna 2: The first tube is now 6' long with a diameter of 1". With the rest of the tube lengths being identical in length and size, antenna 2 will be physically SHORTER because of the extra 2' of 1" material on the first tube.

To be more specific MC, 'Doc how do you figure #2 is shorter than #1 when you've added 2' of 1" material to #2?

I understand what you are getting at, but some might read your post in detail and miss the real point of why element diamater and total surface mass matters. You were going along pretty good there for a bit, then the thingy bit you in the *7%$.

 

[W5LZ]

Marconi,
I guess knowing what is meant, rather than what was actually said, can make a difference. Guilty. What I said still covers what was being talked about, which is what I meant, no matter what I said.
- 'Doc

(working on first cup of coffee. Not sure if that made sense at all. Sounds good though, doesn't it?)

 

[ken white]

Another benefit of a larger diameter antenna is that the BW is increased, or the "Q" is decreased, which is normally a good thing when trying to tune...

 

[Marconi]

I get the picture 'Doc. I just wasn't sure how you came to the fact that:

#1 was 4 x 4' = 16' and

#2 was 6' + 3 x 4' = 18'

and yet #2 ends up physically shorter. Unless you just made a mistake.

I will leave it to BOOTY MONSTER to figure out what you said and how you meant your figures, cause I sure can't.

 

[W5LZ]

...now I'm really confused. Those aren't my figures. Are they? From where?
- 'Doc

 

[Marconi]

Maybe I misread your figures and your remarks here. I am going to take the position that MC has and say no more. I am sure you have explained it as best you can.