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Author Topic: Raising Hex Beam to Roof  (Read 3184 times)
KB3MDT
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Posts: 192




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« on: August 16, 2011, 06:38:37 PM »

Hi,
    I currently have a home brew Fan Dipole (80-40-20-10 Meter) with the center of the antenna on a TV Mast extending above my roof line.   My house (a "Colonial") has a lower roof (above the garage) and an upper roof (above the rest of the house).   Both roofs are "gently peaked" and are easy to walk on.   I have two 10 foot sections of Radio Shack antenna mast.  The first piece goes from the peak of the lower roof, to an Eave Mount, and extends about 2 foot above the upper roof.  The second section is attached to the first, and extends about 12 foot above the upper roof line. Thus, the mast is pretty much above the center of my house. The mast is self guying, as the Fan Dipole has wires extending in all compass directions.       

   I would like to replace the Fan Dipole with a 5 band (20-17-15-12-10) Hex Beam antenna.  I realize I will need to upgrade the sections of Radio Shack mast to something stronger.   I'd like to put a light weight rotor on top of the first 10 foot section of mast which extends about 2 foot above the upper roof line.  I would then have a short mast attached to the top of the rotor and mount the Hex Beam on it.   Thus, the base of the Hex Beam will be approximately 5 foot above the upper roof and somewhere about 25 foot above the ground.    Some folks in our neighborhood have fairly large TV antenna's mounted in a similar fashion.

   My yard is fairly small (100ft by 100ft) and I have power lines down the back property line and one side, so I don't have room for a big tower.  Mounting the Antenna above the center of the house is about my only option.   A roof tripod might be doable, but would be very difficult to reinforce from the underside of the roof as the attic has 20" of loose fiberglass insulation and is all trussed beams.  (I.e. almost impossible to work in).   I have a brick chimney, but I understand mounting antennas on brick chimneys has a way of loosening the bricks from the extra stress and vibration.   I don't think my wife or the neighbors would be too happy about mounting something in the front yard!

  Question #1.   Does the above Hex Beam installation sound doable?   

  Question #2.   I believe you assemble the Hex Beam on the ground, do a few tests, and then raise it to the final position.  In my case, I would probably assemble the antenna in the back yard.  How do you get the assembled Hex Beam (with a diameter of 22 feet) up on the roof?   I have a 34 foot aluminum ladder that easily extends from the ground to the upper roof, plus another that extends from the lower to the upper roof if needed.   My guess is simply carrying the assembled antenna up a ladder is easier said than done.   I have 2 sons (24 and 28 yr old) that can help.   What's your thoughts on the best way to get the antenna up on the roof and mounted to the rotor?

   Question #3.   Any recommendations on which Brand Hex Beam, what diameter and material Masts, and rotor?   
 
   Thanks in advance for your thoughts.
   73.

KB3MDT
Ken 
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W6CD
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« Reply #1 on: August 17, 2011, 05:07:13 AM »

Since the roof is difficult to get a proper tripod or roof tower (like a Glen Martin) mounted properly, instead how about a house bracketed mast extending from the ground up past the higher roof?  Heavy wall chain fence top rail works well - available in various diameters to 24' lengths.
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NJ3U
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« Reply #2 on: August 17, 2011, 06:08:54 AM »

Ken,

I'm working on a very similar installation @ my QTH.  The point you made regarding the attic truss work and insulation is valid, however let me offer this thought.  This is the way I solved the challenges and you can check the photos out on my QRZ bio page via the link.

Cut yourself two foot wide pieces of ply sheathing and attach it to the floor studs of your attic trusses, the small amount of surface space your are compressing of the insulation should not be noticed and this will provide a walkway for you to access the area.

Now that you have that completed, the blocking that is needed on the underside of the tripod or quadpod roof tower is easily accessable.

The plus to all of this is that you will have a new storage area for Christmas Boxes, etc and no risk of stepping through into the second floor ceiling !
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K2MK
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« Reply #3 on: August 17, 2011, 06:17:52 AM »

Be sure to look at the Hex Beam Yahoo site.
http://groups.yahoo.com/group/hex-beam/

If you go to the photo section you will see hundreds of pictures of what people have done in similar situations.

If you can spare the yard space a Rohn H30 push up mast is very popular. Mount the rotator and thrust bearing at ground level on a 4x4 post. Guy the mast at 3 levels using the hardware provided by Rohn. The entire mast rotates. Channel Master makes a similar mast which you may be able to get without shipping charges through your local Ace Hardware store.

I have a Traffie 5 band hex beam which I'm very happy with. The K4KIO is also considered excellent. Read the eHam reviews on both. I use a Yaesu G-450A rotator and GS-050 thrust bearing.

73,
Mike K2MK
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KA5N
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« Reply #4 on: August 17, 2011, 07:26:39 AM »

Getting the Hex on the roof is a bit akward but, depending on the height of the roof
edge (and the amount of extra hands you have) it is not all that hard.  You can easily
pick the assembled antenna by the spreaders and lift the Hex over your head and angle
the spreader up to the edge of the roof and have a helper pull the antenna up as you
push.  If the edge of the roof is 10 feet or less this will work.  Trying to stand on a ladder and move the Hex about is difficult and dangerous. 
Don't use fence railing for a mast for the Hex it is too flimsy.  Even the masts by Rohn and Channel master are a bit flimsy (top section) and guying properly is critical.
Putting the rotor at the bottom works best and keeps weight off the upper end of the mast.  If you use a thrust bearing at the level of the lowest mast section a G-450 will turn the Hex easily and give few if any problems.
I have a Hex and it does a great job at low heights (around 20 to 35 feet) which are
easier to achieve than 40 or more feet.
Good Luck
Allen
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K2DC
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« Reply #5 on: August 17, 2011, 01:28:48 PM »

Ken,

   There's no doubt it's doable with some careful thought ahead of time.  I used a similar installation at a previous QTH for 2m and 440 Boomers with El over Az rotors for satellite work.  The lower mast was secured to the garage roof of the colonial with an adjustable V shaped bracket, and secured to the main house with a house bracket.  The lower mast was just long enough to put the Az rotor above the roof line, and the upper mast just long enough to allow full elevation rotation of the boomers.  Just a couple of thoughts:

-  You're right - chimney straps are a formula for disaster.  It may take several years, but brick (or wood, lathe and plaster) chimneys are never designed for the wind and torque load of an antenna that size.

-  5' above the main roof may not be enough at HF.  I had a mini-quad once that worked very well for me in a more open installation.  When I mounted it as you are proposing, it was not nearly as well matched and the performance stunk.

-  Choose your mast material carefully.  As long as you rotor has the guts to take the dead weight, steel gas pipe works great.  I used an Alliance HD-73 for my roof mount that worked well, and you can find them reasonably priced on the used market.

-  I've never had any experience with a rotor mounted at the bottom.  But I would make sure that all of the masts are precisely vertical.  Otherwise the off-axis loading can make short work of the bearings.

GL & 73,

Don, K2DC


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WA8FOZ
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« Reply #6 on: August 18, 2011, 08:58:33 PM »

Quote
Putting the rotor at the bottom works best and keeps weight off the upper end of the mast.  If you use a thrust bearing at the level of the lowest mast section a G-450 will turn the Hex easily and give few if any problems.
and
Quote
I've never had any experience with a rotor mounted at the bottom.  But I would make sure that all of the masts are precisely vertical.  Otherwise the off-axis loading can make short work of the bearings.
I agree. With that proviso, this can be a very good way of putting up a light antenna, such as a hex beam. I have done this several times with a small tribander, and it has worked well for me.

If you do this you may still be able to keep a dipole up for 40 and 80.

73,
Bill WA8FOZ
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