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Author Topic: Rohn 25AG  (Read 1242 times)
N0DSN
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Posts: 13




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« on: January 12, 2010, 04:11:24 PM »

I am looking at putting up my first rotor (Ham IV) and a HF beam (Mosley TA33 JR). What I am wondering is I have a TB50 bushing installed at the tower point already. Do I need a thrust bearing to go along with this. If so what thrust bearing plate would be work for this setup. I realize I need the rotor shelf it self but dont know about the thrust bearing. Like I said first time install and any help would be greatly appreciated.

KD0BFP
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K3GM
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« Reply #1 on: January 12, 2010, 08:02:23 PM »

Actually, the peened bushing that comes installed in the 25AG "rocket top" tower section would have sufficed.  I used one with a TH3JR for 4 or 5 years without problems.  The Ham IV will support the vertical load of your tribander without the aid of a thrust bearing.  Should you choose to add one, I believe you'll need to place the rotor shelf at the bottom of the section, while installing the bearing on a second shelf in the traditional rotor location.  I also think you'll need to drop the rotor down thru the top section and onto the pre-mounted shelf at the bottom in order to avoid "surgery" on the lattice.  Then once the thrust bearing and mast are in place, you can't remove it if it ever needs servicing.  Your existing setup will work fine.
« Last Edit: January 12, 2010, 08:04:38 PM by K3GM » Logged
WB2WIK
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« Reply #2 on: January 12, 2010, 10:12:26 PM »

That suggestion should work.

But I always wonder why "anybody" chooses the welded tube top section.  Having installed a lot of 25G towers, I would never install the welded tube top section; it's too limited in its utility and can create rotator to mast alignment problems.  It also doesn't provide guy points for the top section.

For the same cost, you can get a "beacon plate" top, which is flat, provides three very good guy brackets, has the top plate pre-drilled for a thrust bearing, and does everything the other top sections do.  No extra cost, and more versatility.

The "rocket top," "pointy top" or "welded tube" top section would be my very last choice in installing a 25G.
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K3GM
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« Reply #3 on: January 13, 2010, 05:12:48 AM »

......I always wonder why "anybody" chooses the welded tube top section.......

My guess is there are probably plenty of them out there from used TV antenna installations.  ....and I imagine many of them are RG-20 sections and are used unknowingly.  Another mistake a new user makes is to try and cut costs.  The flat top section runs about $60 more, and bearing costs anywhere from $125-$175 these days.  If you can, I'd also recommend using either a full section with the short beacon top plate on top (BPL25G), or the 8 flat top section (25AG4).  Take the rocket top section to a hamfest.
« Last Edit: January 13, 2010, 05:15:17 AM by K3GM » Logged
WB2WIK
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« Reply #4 on: January 13, 2010, 11:44:06 AM »

I use the Yaesu thrust bearings, which are cheaper. Smiley  And they fit the Rohn plates just fine.
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K9KJM
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« Reply #5 on: January 14, 2010, 12:01:51 AM »

For a smaller HF beam like the TA33JR NO type of "thrust bearing" is needed. I had one up for well over 10 years in the common (old used Rohn 25G "TV" tower recycled into a ham tower, With the tapered top section)
As properly pointed out, Old used TV towers are CHEAP to obtain, And the taper top section works very well. The much more expensive ball bearing type "thrust bearing" is needed only if you go with a really BIG antenna array.   IF you have a really large array and will be using the ball bearing type thrust bearing, Then the "flat top" section is much nicer.

In fact, You could have a TA33JR just above the tower, A two meter yagi above that, And a high gain VHF/UHF dual band vertical at the top of the mast and have NO problems with the common "taper top" Rohn 25G. Lots of us have already done that and proven that.
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N0DSN
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« Reply #6 on: January 14, 2010, 04:42:05 AM »

Thanks for all the help in the replies. As far as the "Cheapness" of the tower goes. Yes did pick it up cheap from my brother's inlaws just for taking it down.
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