What to use for a Mast on a Rohn HDBX48 Tower

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by W4MRP, Apr 17, 2019.

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  1. W4MRP

    W4MRP Ham Member QRZ Page

    OK. First tower. Restoring a old Rohn HDBX48 tower inherited from a silent key friend of the family. I also have his Mosley Pro 67-A ("A" model out of production but does 40,20,17,15,12,10) that he had on this tower for at least a couple of decades. I want to keep this tower and antenna together just like he had them. By the time the tower got to me, the mast, thrust bearing and rotator had been removed. Planning on an Alfa SPID RAK rotator with Green Heron controller. Have a fancy DX Engineering thrust bearing on order and a new hardware kit for the tower with new bolts and such.

    Anyway, a Rohn M200H mast is about $200 not counting shipping. This is a 10-foot, 2" OD mast with 11 gauge thick walls. I can't determine if it's just mild steel or harder carbon steel. Does anyone know what type of steel is in the M200H mast?

    If it's just mild steel, seems that something like Schedule 40 water pipe would work just as well.

    Any suggestions on what else I might use for a mast? Any suggestions for masts from other tower companies? Would like to stick with steel rather than aluminum for this big Mosley beam. 10 feet sounds like a good length. Maybe 15 at the most.

    Thanks and 73s!

    --- Mike, W4MRP
     
  2. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    It's high carbon steel and very strong. $200 isn't a bad price for that. An alternative is Chromoly steel, and a 10' length with .188" wall thickness goes for about $244.

    Rohn M200H.PNG
     
    W4MRP likes this.
  3. K3XR

    K3XR Ham Member QRZ Page

    Check if you have any scrap yards in your area. All my quarter wall aluminum mast came from there purchased at a per pound scrap aluminum price. That was well over 40 years ago and they are still in use on a couple of towers.
     
    W4MRP likes this.
  4. W4MRP

    W4MRP Ham Member QRZ Page

    Thanks! Whar yew gettin the chromoly steel mast for $244? Got a link?

    'Preciate it!

    --- W4MRP
     
  5. W4PG

    W4PG Super Moderator Volunteer Moderator Platinum Subscriber Life Member QRZ Page

    Do you need a building permit to put up the tower??

    I had an old HDBX56 back in the 70s. Rohn always advertised those HDBX towers as "not designed for twisting motions" and they listed a fairly small boom as the maximum length. I think it was 10 feet or so but I don't remember. Folks typically ignored that. The info I came across suggested your 48-foot tower was rated "up to" 20 square feet in 70 mph winds (3 second gusts). If you need a building permit, you might have a real problem getting permission since there are few places in the entire US where those towers meed current wind-load requirements. You might want to check your local building requirements before you spend a lot of money only to find you can't get a permit. It's happened many times before.

    Good luck!

    PS: I had a 3 ele QUAD for 10-15 and 20 on my HDBX56 and got a 2-inch OD water pipe for the hardware store. It did fine. DO NOT run the mast more than a couple of feet above the top of the tower! Again, those towers were not designed for large antennas that twist.

    ................Bob
     
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  6. W4PG

    W4PG Super Moderator Volunteer Moderator Platinum Subscriber Life Member QRZ Page

    K0UO and W4MRP like this.
  7. W4MRP

    W4MRP Ham Member QRZ Page


    Thanks Bob! I realize the Mosley Pro67 (24ft boom, ~12 sqft wind load) is a big antenna for that tower. However, that antenna was on that same HDBX-48 tower for about 25 years on a mountain top environment with a rotator. All the aluminum rivets are still tight too -- a common failure mode of these towers caused by torsional stress from what I read. Also I ran across a post on the TowerTalk reflector where the moderator, Steve K7LXC (and author of the "Up the Tower" book which I own), indicates that the HDBX is strong enough for longer boom lengths.

    Tower just has a little surface rust where the galvanizing is failing. I've treated it twice with Ospho (phosphoric acid rust converter), letting it dry and angle grinder brushing it off in between applications. Ospho makes paint stick to metal good in my experience. Have a gallon of ZRC Cold Galvanizing Compound I'll paint it with (roller and brush, with a few spray cans for hard to reach areas). I'm also getting a new hardware kit for it with new tower leg bolts and all (although the original stainless bolts look fine to me). I will fabricate a new top plate and router plate out of some 1/4" steel plate I have here already, bordered with 1.5" angle. Existing ones seemed kinda flimsy. Also, the Green Heron rotator controller has a soft start feature that ramps up the rotator speed to keep stresses low. Considering running a pipe up the middle and rotating from the bottom to 1) keep rotator at the bottom and 2) virtually eliminate torsional stress on the tower. Anyone ever done this?

    Thanks!

    --- W4MRP
     
    Last edited: Apr 17, 2019
  8. W4MRP

    W4MRP Ham Member QRZ Page

  9. W4MRP

    W4MRP Ham Member QRZ Page

    You got big antennas on those aluminum masts? A Mosley Pro67 has a 24 foot boom with 42 foot wide 40m elements. Weights around 120 lbs.

    --- W4MRP
     
  10. K3XR

    K3XR Ham Member QRZ Page

    Had, for a time, a 4 element Cush Craft 20 meter Skywalker beam on a 60 foot E-Z Way tower. I can't say how it would support a Pro67, that is a very big antenna. Would check the specs for the wall thickness you plan to use.
     
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