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Author Topic: Why the Bladed Spiders on 5BTV Vertical?  (Read 2906 times)
WA9YSD
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Posts: 138




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« on: May 23, 2012, 11:27:12 AM »

Why do they use the 3 bladed Spider under the 80M coil, and the 6 bladed spider above the 40M trap on the Hustler 5BTV vertical? What are there purpose?  Is placement critical?

Jim
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KQ6Q
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Posts: 979




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« Reply #1 on: May 23, 2012, 11:36:04 AM »

I suspect that these are 'capacity hats' and their placement is critical to tuning the antenna. When in doubt, follow the directions....
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WA9YSD
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Posts: 138




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« Reply #2 on: May 23, 2012, 12:01:52 PM »

Why not design it with out them?

Why did they build it with them?

Jim
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W9GB
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Posts: 2623




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« Reply #3 on: May 23, 2012, 02:26:31 PM »

They are capacity hats.  
IF you don't like them, BUY the Hustler conversion kit to
Convert your 5-BTV to the 6-BTV (adds 30 meters).
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K1WJ
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Posts: 455




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« Reply #4 on: May 23, 2012, 02:43:39 PM »

Capacity hats will reduce the amount of inductance necessary to resonate the antenna, and increase bandwidth. But contrary to popular belief they add nothing to the radiation resistance. For a component of an antenna to increase radiation resistance it must itself radiate.

It is true if you put a Capacity hat on top of a short mobile antenna it will change the antennas efficiency but what happens is the current on the radiating element moves further up to the top.

Because the current is now further away from ground this lowers ground loss. So the ratio of radiation resistance to ground loss and Omni Loss resistance, which is the reduction in the amount of inductance needed for the loading coil, goes down.

73 K1WJ
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WB2WIK
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« Reply #5 on: May 23, 2012, 02:59:13 PM »

Why not design it with out them?

Why did they build it with them?

Jim

Because they use the same traps in other antenna models that don't use the "spiders."

It's probably cheaper and easier to make traps that are common to all models, and then alter the models, than it would be to make the traps differently.
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WX7G
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« Reply #6 on: May 23, 2012, 04:07:22 PM »

The five spoked thing appears to do nothing but look cool. I've tested a 5BTV with and without it.

I've used the RM-80S resonator without its spider and it works fine.
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W8JX
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« Reply #7 on: May 23, 2012, 05:52:22 PM »

The five spoked thing appears to do nothing but look cool. I've tested a 5BTV with and without it.

I've used the RM-80S resonator without its spider and it works fine.

Yea I am sure that Hustler just wastes time and money shipping antennas with them. Yea right. Bet you did bandwidth and field strength tests too.  A "hat" will increase the efficiency of a antenna for a given size. The trade off is is add mass and wind loading to top of antenna. 
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WA9YSD
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Posts: 138




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« Reply #8 on: May 23, 2012, 10:23:07 PM »

It sure likes to wip up in the wind.

Reason why I asked was I made a home brew trap vertical. 40 and 160M is working just fine. 80 has issues. Looking for the best place to put some wire for capacity to draw the current and radiate.  I would suspect that at the top of the 40M trap would work out better than just below the 80M trap. Then again I am probably wrong.

Jim
« Last Edit: May 25, 2012, 11:06:51 PM by WA9YSD » Logged
KA1MDA
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« Reply #9 on: May 24, 2012, 04:45:25 AM »

The five spoked thing appears to do nothing but look cool. I've tested a 5BTV with and without it.

I've used the RM-80S resonator without its spider and it works fine.

Isn't the spider on a 5BTV BELOW the 80 meter resonator? For a capacity hat to work, it's places at the top of the radiating element. I think the spider below the 80 meter resonator is used on 40 meters, not 80. Just because it's physically next to (below) the 80 meter resonator doesn't mean it's part of the 80 meter portion of the antenna.
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KG4RUL
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« Reply #10 on: May 24, 2012, 08:15:39 AM »

I remember seeing a suggestion on their website to remove the "spiders" and enclose the antenna in a piece of PVC pipe so it looks like a flagpole.
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WA9YSD
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Posts: 138




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« Reply #11 on: May 24, 2012, 08:40:22 AM »

Capacity hat antennas have a hat on top of the vertical thus the term CAPACITY HAT.

The only 2 antennas I have seen that had loading elements have been the Hustler vertical and a Battle Creek Special.  Am I off topic now?

I think I will start a new topic called Capacity Hats and Loading Elements for Verticals.

Jim
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KA1MDA
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« Reply #12 on: May 24, 2012, 09:56:56 AM »

The capacity hat doesn't have to be PHYSICALLY at the top of the antenna to be a capacity hat- it has to be at the top of the ELECTRICAL section of the antenna. Since the BTV is a multiband trap vertical, there are multiple "tops" to the antenna. the electrical top of the 10 meter portion is just below the 10 meter trap. The electrical top of the 20 meter section is just below the 20 meter trap. You could install a capacity hat at either of those locations. It doesn't matter if they are not at the very top of the antenna physically, they are indeed at the top of each resonant section electrically, which technically still makes them capacity hats. As far as RF is concerned, the rest of the antenna above the trap for that band doesn't exist.
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WX7G
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« Reply #13 on: May 24, 2012, 10:43:26 AM »

I remember seeing a suggestion on their website to remove the "spiders" and enclose the antenna in a piece of PVC pipe so it looks like a flagpole.

Yes here is the link to the QST article: http://www.dxengineering.com/pdf/flagpole_antenna.pdf

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W0FM
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Posts: 2055




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« Reply #14 on: May 24, 2012, 01:36:38 PM »

Back in 1989, I took the capacity hats off my BTV antenna so I could insert it into a PVC "flagpole" and the only difference I noted was slightly reduced bandwidths.  My rig's tuner made it work.

Side note.  I just clicked the link and read the DX Engineering article on Al Parker's BTV flagpole from 1993.  Was a bit shocked to see myself referenced (I was NØDFH back then) and credited in Al's comments regarding the use of an upside down bucket to conceal the BTV mounting post.  Time flies when we're all having fun.

Terry, WØFM
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