Disecting a vertical antenna

[737mech]

Take a look at this picture, (best I could do with MS Paint) anyway, I had this old antenna, it broke, so I pulled it apart. Interesting to see how the coax coiled and terminated near the top of the vertical section and the shield terminated at the top of the lower section? Note that in the top portion you have isolation with dilectric but no shielding for the center conductor to the top. The upper and lower portions are made of brass and as noted on the drawing they are isolated from each other. Also the coil is interesting, I'm guessing for TX loading? I'm no expert on antennas, I just pulled this apart to see what it was made of. It was originally for VHF airband made by a company called "Celwave" or something like that. Any thoughts? Why was it built this way? What does bringing the center conductor to the top do for you? Any other coments welcome.

 

[prcguy]

Looks like a center fed "coaxial dipole" with the coil at the bottom being the coax wound into a choke to decouple RF from the feedline. Let us know if the coil is actually the coax.
prcguy

 

[737mech]

vertical

Looks like a center fed "coaxial dipole" with the coil at the bottom being the coax wound into a choke to decouple RF from the feedline. Let us know if the coil is actually the coax.
prcguy

Yes it is the coax that makes up the coil.

 

[prcguy]

Is this in a white plastic tube about 1 1/4" dia with a threaded chrome plated base that screws into a black aluminum mount with two U bolts?
prcguy

 

[737mech]

vertical

The radome was severe sun burned like pvc gets but was about 1" diameter and the chrome part you are correct, the base was gray cast aluminum two u bolts. I'm still wondering why the coax center conductor was run all the way to the top why not just to the bottom of the element? Seems it was done for a reason?

 

[N_Jay]

The coax is run to the feed point of a simple dipole.

 

[prcguy]

Sounds like you have a Cellwave BA-1010 series. The upper portion and lower portion in your dwg would be the dipole elements and its fed at their junction. probably with miniature Teflon coax about 1/8" dia and brown in color.

I have several in other frequency ranges.
prcguy

 

[737mech]

vertical

Sounds like you have a Cellwave BA-1010 series. The upper portion and lower portion in your dwg would be the dipole elements and its fed at their junction. probably with miniature Teflon coax about 1/8" dia and brown in color.

I have several in other frequency ranges.
prcguy

Ok, so now I know who made it, thanks for the info prcguy, but questions about the construction?? Why take the feed line all the way to the top? What changes if you feed it half way up the vertical or at the base of the top piece? Does someone have an idea why it was engineered this way?

 

[N_Jay]

Does someone have an idea why it was engineered this way?

YES!

Because that is how a dipole is designed.

Face to face with a white board, it would not be hared to explain, but in this format/forum, I will leave it to someone else.

The biggest challenge is figuring out where you are starting from in terms of basic RF waves and fields understanding so the explanation can use appropriate analogies without insulting you.

If you are really interested, I would suggest a good book on antennas, like some from the ARRL.

 

[737mech]

Vertical

YES!

Because that is how a dipole is designed.

Face to face with a white board, it would not be hared to explain, but in this format/forum, I will leave it to someone else.

The biggest challenge is figuring out where you are starting from in terms of basic RF waves and fields understanding so the explanation can use appropriate analogies without insulting you.

If you are really interested, I would suggest a good book on antennas, like some from the ARRL.

Thanks for explaining without insulting, I had someone at work suggest the same thing ARRL book. Wish that was a seperate forum. (ARRL handbook)

 

[N_Jay]

Thanks for explaining without insulting, I had someone at work suggest the same thing ARRL book. Wish that was a seperate forum. (ARRL handbook)

Glad you are not insulted, because you would not believe the number of people who consider;
a) "This is the type of subject better understood if read",
and/or
b) "It is hard to give you an answer without knowing what you already understand,"
as sever insults.