My First Attempt At A Mobile Antenna

[HomerBB]

Well that's a boat load of information, Doc, and very useful.
I will spin another coil as suggested. I certainly need to get it shorter without overly compromising the performance radically.
Looks are important for personal satisfaction, but performance matters more at this point.
As for the copper, it is simply the least expensive material I have considering it was at hand. I will be going to something else, probably aluminum rod. I am equally interested in the weight as I am the integrity of it.
As for the insulators, I don't run much power - 100 watts at most - so Delrin won't be the only choice. I have been looking at epoxy poured into a PVC tube for the coil core, and looking into cutting board cut-outs for the bottom bracket insulators.

Thanks for the input.
Homer/Charles

 

[office888]

Homer -

your antenna has excellent SWR because the coil is located above the top of the roof of your mobile. A loaded antenna (one with a coil) radiates from the top of the coil. The stinger is there ONLY to provide matching to as close to 1:1 as possible. Increasing the wire size (or surface area) of the coil will increase the bandwidth and keep the swr low over a wider freq range. Your antenna is excellent in this respect. Increasing the diameter of the stinger will also increase your 2:1 bandwidth, which is a good thing. Disregard the Bullsh-- posts from persons in this forum who don't have a clue.

- 399

I'm still pretty new to antenna theory.

Could someone explain the science behind this?

Please and thank you!

 

[Mr Clean]

They have spray rubber coating that I used on the non stainless screws on my beam. I wonder if it would work well for a coating for your antenna? Maybe not at 10 killowatt but for us ducks lol.

http://www.google.com/products/cata...sult&ct=result&resnum=1&sqi=2&ved=0CBsQ8wIwAA#

 

[HomerBB]

Maybe . . . Hmmm

 

[W5LZ]

"Increasing the diameter of the stinger will also increase your 2:1 bandwidth, which is a good thing. Disregard the Bullsh-- posts from persons in this forum who don't have a clue."

That's some fairly good advice. At least, the second sentence is. The first sentence requires some explanation, and that ought'a be interesting. If you could quantify the amount of increase in the 2:1 SWR bandwidth with the amount of diameter required, that ought'a be really interesting!
- 'Doc

 

[mackmobile43]

"Increasing the diameter of the stinger will also increase your 2:1 bandwidth, which is a good thing. Disregard the Bullsh-- posts from persons in this forum who don't have a clue."

That's some fairly good advice. At least, the second sentence is. The first sentence requires some explanation, and that ought'a be interesting. If you could quantify the amount of increase in the 2:1 SWR bandwidth with the amount of diameter required, that ought'a be really interesting!
- 'Doc

But doesn't his first sentence contradict the second? why would anyone make claims without explaining with cold hard facts thus leaving speculation of even more bullshit.

 

[BOOTY MONSTER]

"As for the insulators, I don't run much power - 100 watts at most - so Delrin won't be the only choice. I have been looking at epoxy poured into a PVC tube for the coil core, and looking into cutting board cut-outs for the bottom bracket insulators."

i just run a pair of 1446's myself . the recycled plastic lumber i use has passed my extremely high tech %100 fool proof accurate microwave oven test . LOL
a 2x2 piece would be easy if you have a lath

 

[HomerBB]

I love the give and take of these discussions. From here, everyone gives me advice, and I take the part I can use. If it don't work, I give it back.

I could look into the composite decking as a potential alternative to Delrin, I suppose. I oughta have a perfect piece of that in the closet somewhere . . .

 

[mackmobile43]

"Increasing the diameter of the stinger will also increase your 2:1 bandwidth, which is a good thing. Disregard the Bullsh-- posts from persons in this forum who don't have a clue."

That's some fairly good advice. At least, the second sentence is. The first sentence requires some explanation, and that ought'a be interesting. If you could quantify the amount of increase in the 2:1 SWR bandwidth with the amount of diameter required, that ought'a be really interesting!
- 'Doc

Still waiting for 399's reply to this one.op:

 

[HomerBB]

Today I rewound a coil of 3 wraps and 5" diameter and 6" top to bottom. The SWR curve is roughly the same as it was, but the antenna is 14" shorter now. The present redone coil is made of 1/4" copper pipe, so is really ugly. I will not keep the pathetic little spindly looking coil. More changes tomorrow. It has gotten dark and supper approaches so I pulled the SUV into the garage for tonight. I don't know if the performance will suffer with the changes until tomorrow.
We'll find out.

 

[HomerBB]

Okay. Some more photos of the build. I haven't the time right now to do a 1-2-3 break down, but I will respond to any ques later.












Oops! Coil was wrong. I wanted 5" x 6" x 3 turns. Fixed.

 

[W5LZ]

You know, I'll bet that if you had wound that 'bar' stock 'flat' instead of 'on edge', you could have knocked another couple of inches off of the antenna's height.
Something else to think about is that by making the coil's shape more efficient, you are raising it's 'Q'. Wanna be sort of careful about that, the higher the 'Q' the less 'bandwidth' that antenna will have. The higher the 'Q' the higher the efficiency, but the narrower the usable 2:1 SWR bandwidth. Sounds like you can 'improve' an antenna too much, doesn't it? Or does it just mean that a really 'wide banded' antenna is less efficient? Hmm...
- 'Doc

 

[BOOTY MONSTER]

using larger diameter material can help an antenna be more broad banded too from what i understand . more surface area doesn't make it louder or have a stronger signal though .

 

[HomerBB]

It remains very wide banded like it is, however, because i wander not very far from the CB 40 in the mobile I don't need too much bandwidth. I may try a shorter center insulator to get the coils closer as per a suggestion; just to see what happens.

 

[ROC1]

Homer -

Your antenna design is good...just keep things within design parameters for the freq you're looking to work. Otherwise, look to keep the 2
:1 bandwidth as wide as possible using the techniques we discussed earlier.

- 399

A wide banded coil also has a lower Q... If he's going to use it on a single band there is no point in optimizing the 2:1 characteristic... it may make sense to make it as efficient as possible for the intended frequency.