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Author Topic: Advice on attaching pulley to top of mast for my dipole  (Read 12557 times)
KD2CJJ
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Posts: 369




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« on: August 14, 2012, 10:57:40 AM »

Need some advice for my Fan Dipole that currently comes off the side of my 2 story house...  I want to raise the antenna 10 feet (using a 10 foot mast makes it 35 feet in total) and extend the top of my mast perpendicular out away from my house about 6 - 10 feet then attach a pulley (like hang man) see below pictorial

Any ideas (using local home depot materials ideally)?
__________
|                 V
|                 o       <----away from my house
|
|
|
|   <---- against my house





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73

Mike
KD2CJJ
KC9QQM
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Posts: 184




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« Reply #1 on: August 14, 2012, 11:05:27 AM »

So I take it you don't have a tower? Just a mast pipe up the house? I would think you might be able to find some type of 90 elbow to go from the verticle pipe to the horizontal and then you would want to put a diaginal rod or bar up so all the stress is not on that elbow. You could use a piece of 3/4" conduit and hammer it flat on the ends and drill a hole through it and then drill a hole in the pipes and bolt it to it.

While I do have a tower, I am doing what you describe to get my fan dipole out from the tower. Look at my photo on QRZ;
http://www.qrz.com/db/KC9QQM

You cannot see it too well but I am using a 3/4" conduit as the horizontal bar. I ran it through the tower so I have the extra bracing for the downward pull.

Good luck and 73,

Jeff
KC9QQM
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KD0REQ
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« Reply #2 on: August 14, 2012, 11:07:05 AM »

get a dowel (plastic if you can) to put in the top of the mast.  get a 1/4 inch long eyebolt, assorted nuts, lockwashers, etc for both sides of the bolt end.  drill it in there, put the foldover gap of the bolt up.
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AC5UP
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« Reply #3 on: August 14, 2012, 11:09:59 AM »

...extend the top of my mast perpendicular out away from my house about 6 - 10 feet

Six to ten feet of overhang adds a remarkable amount of leverage to the top section of the mast and it's leverage trying to pull the mast away from the house. If you hang the dipole a little too tight (and a fan dipole needs tension on multiple wires which all pull on the center support) you'll see a mast failure or the bracket(s) pulling away from the house.

I wouldn't go more than two or three feet on the overhang, and a cross brace wouldn't hurt a thing.
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AA4PB
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« Reply #4 on: August 14, 2012, 11:40:39 AM »

You can also move the lower ends of the antenna away from the house to provide separation without having such a long horizontal support.
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W4VR
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« Reply #5 on: August 14, 2012, 12:00:55 PM »

If you use a pulley, make sure you buy one of the marine ones where the rope can't go off the track.  The other option you should consider is a big eye bolt; this way you're assured that your rope does not get tangled up or off track.
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KD2CJJ
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« Reply #6 on: August 14, 2012, 12:22:30 PM »

Thanks for the advice - regarding the mast - its a 16 guage steel mast - it should support anything I throw at it (except a large beam) and I intend to reinforce the wall brackets in my attic with 2x4 cross beams - no way in hell it will come out without taking out the side beams supports of the house -

I will need to make a trip to home depot and see what I can slap together that wont fail.. I suspect I will need something that can support 20lbs...  Maybe 3  - 4 feet should be sufficient with the extra height... and the extra height will actually only equate to no more then 6 - 7 feet as I will need about 3 - 4 feet to attach to to the bracket.  Maybe a pull is not the best idea--- I think the eye bolt actually would work better in the long run...

Im doing this to serve two purposes  1.  Get it higher for a better take off angle, 2.  to get it in the clear from the house.. right now the apex of the V is against my house - I am most likely incurring some level of reflection and absorption.... getting it higher than the house should yield a better radiated signal while reducing SWRs..

My other issue is that I am not at 90 Degrees.... I havent figured out how to get the ends higher as one end of the V I have run out of yard to tie down the end...the other end I can go pretty far with no issue but I also have to contend with wife...  any ideas on this one?
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73

Mike
KD2CJJ
N6AJR
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Posts: 9927




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« Reply #7 on: August 14, 2012, 12:44:33 PM »

No need to extend the mast out from the pole. Get the center up as high as you can with reasonable effort and then mount your pulley there and haul up the antenna. You can also use a piece of wood dowel for the top couple of feet of the mast and hook  the pulley up there. You can put the fan dipole out in  a one under the other style or you can put it up in the umbrella or Astrix fashion, with one pair going north south and the next pair going east west and the next pair caddy corner  to that.  this makes them easier to tune, and also supports the mast better. you don't even need a "real" pulley, just a large eyebolt for the rope to slid through will do OK.  google fan dipole and check it all out.
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KB3LIX
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Posts: 1130




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« Reply #8 on: August 14, 2012, 01:36:55 PM »

Remember to put a tag line from the top rope
and antenna
back down to the ground.

If for some reason, the antenna comes loose and falls,
if you don't have the tag line, how are you going to get the rope back
down to the ground to repair the whole she-bang ??
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WB6BYU
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Posts: 13574




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« Reply #9 on: August 14, 2012, 03:30:37 PM »

I use a piece of 1x2 or 2x2 wood with a U-bolt to go around the mast.  Actually I make
them about 3-4' long with the U-bolt in the center and a screw eye on each end, so I
can hang two halyards on the the mast.  Never know when you might want to try out
another antenna...
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AA4PB
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Posts: 13032




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« Reply #10 on: August 14, 2012, 04:02:10 PM »



 _____|__________
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       .   |
         . |
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It's also possible to do this sort of thing to permit cable to be used for the arm support.
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KB3MDT
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Posts: 208




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« Reply #11 on: August 14, 2012, 04:44:41 PM »

Hi, I have a mast (2 sections of Radio Shack Steel Mast,each 10' Long) that extends from my lower to my upper roof, and then 12 foot above the upper roof. My Fan Dipole Antenna goes "Up and Over" the house.   I'm not sure if this is an option for you.

Anyway, I placed a piece of PVC pipe, about 12" long, over the top foot of the mast.   I then drilled a hole through the PVC Pipe and the mast.  I placed a long (About 4") 3/8" eye bolt through the holes, holding both the eye bolt and the PVC Pipe in place.   I then used an "S" link to attach a plastic Clothes Line Pulley  (About 3" diameter) to the eye bolt.  I then used 3/8" black UV Resistant Rope to hold up the center insulator of my FAN Dipole.  The rope is about twice the length of the pole so that I can drop the center insulator to my lower roof and still have the other end of the rope low enough to reach to pull it all back up.  Everything but the rope was from Home Depot and Mast from Radio Shack.  Go to your favorite internet Amateur Radio site for the rope.

Some comments and observations.   The first time I did this, I used a Wire rope with vinyl coating and an all metal $4.00 1" pulley from Sears Hardware.  The pulley keep rusting so that it wouldn't turn properly.  The Wire Rope would get a permanent ""U" in it from the pulley and would hop off of the pulley.    One wire of the Fan Dipole would get too close to the Mast and mess up my SWR.

Thus, the following changes on verson 2 a few years later.  I added the PVC Pipe Sleeve at the top of the mast.  This guarantees I'll never have a wire directly shorting to the mast.   I switched to "Double Braided Polyester Antenna Rope"  (WWW.SyntheticTextiles.com - but I ordered it elsewhere).  Don't try regular rope, it will "rot out" in the sun in a year or two.  I switched to a bigger diameter "Clothes Line" pulley with the center being plastic and the metal bracket being aluminum.   The only gotya I have now is that the 3/8" 4" long Eye Bolt will bend over time.  However, even with a 45% angle bend, everything works okay. 

Pictures are on QRZ.COM   (Search for my call sign KB3MDT or try http://www.qrz.com/db/KB3MDT)

73
Ken
KB3MDT
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G8JNJ
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« Reply #12 on: August 15, 2012, 12:31:07 AM »

Hi,

Another point to consider - what are the other ends of the dipole attached to ?

If you are using trees as anchor points you need to allow for some movement of the dipole flat top section.

I use pulleys at both ends of my dipole. One end of the dipole support rope goes over the pulley and down to the ground where it is tensioned with bungee cords. The other end of the dipole support rope goes over a pulley and is held under tension by some concrete blocks hanging on the end of the rope. Adjust the weight of blocks and tension of the bungee cords to get the tension and position of the flat top set correctly.

Use enclosed marine grade pulleys with ballraces, of at least 2" in diameter (the larger the diameter the better), for smooth operation. Small ones will just jam.

Use a length of bungee cord at the ground level fixing to tension the rope from the middle pulley, so that it can move about slightly. Put a loop in the feeder so that it isn't holding the centre of the dipole under tension, instead of the pulley and rope.

Before I did this I found a lot of forces were transmitted to the dipole support attached to the house. When it was windy this manifested itself as a 'thumping' noise transmitted through the brickwork, which used to wake me up at night. That was until the fixing bracket finally sheared off the brickwork.

Since using the method described above, I have had no problems.

Regards,

Martin - G8JNJ

www.g8jnj.webs.com

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K1CJS
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Posts: 6061




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« Reply #13 on: August 16, 2012, 04:51:51 AM »

As someone stated, the leverage of the horizontally extended 'hanger' mast will put tremendous strain on the mast mounting point to the house.  Even if you counterbrace that horizontal mast to the opposite side of the vertical, the leverage on the vertical will still be there.

A horizontal hanger mast extending out one or two feet should be plenty, but if you must have that amount (6 to 10 feet) of horizontal separation, plan on guying the top of the vertical mast to a point directly opposite the direction of the horizontal extension, or double guying the top to two points opposite the horizontal extension.  You may also want to note that you'll have a tremendous amount of downward pressure on the vertical mast with that much overhang and the guying needed.

Finally, the mechanical leverage produced by the tension of the antenna and the distance of horizontal overhang and/or the downward pressure on the assembly will tear the mounts off the house sooner or later even if it is heavily anchored at the inside, or you'll gradually make a pretzel out of the masts themselves!  73 and good luck!
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KD2CJJ
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Posts: 369




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« Reply #14 on: August 16, 2012, 01:36:46 PM »

Thanks for the great feedback guys!!!!  I see extending it out really wont help all that much ---- so I am going to abandon that idea. 

I like the idea of the dowel - or PVC covering the mast.... with the eye bolt... I am using an Eye Bolt now on the side of my house and its working... I just need more height and why this project...

My only concern with my setup is that the apex will not be 90 degrees (or more)  unfortunately one of the ends will be at a very sharp angle down as I run out of property... the other side I can tie it off further out though to pull it away... 

Have you guys ever rigged the center of the dipole to fan out the ends away from each other - have any ideas?

Also, my dipole is a AlphaDelta DXEE which uses insulated wires - is this still an issue if it is close to the mast?
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73

Mike
KD2CJJ
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