What setup would work better?

[Captain Kilowatt]

My GM has been on a chimney strap mount and a 14 foot mast for the last two years. About a year ago I cut the mast just above the chimney to install a HD-73 alliance bell shaped rotor. The next week I installed a 4 element yagi about 9 feet below the GM. The two things I'd like to point out are I carefully tested the performance of the GM before and after the Yagi was installed under it. No change at all could be detected in GM's VSWR or the signals of any local stations I had been working. Bell shaped rotors are usually much stronger than the design Radio Shack sells. A friend a few towns away did the same install with an Antron 99 and Radio Shack rotor. The housing of the rotor broke and took both antennas out with it.

I personally would NEVER even consider using a typical Radio Shack type rotator and would always go with a bell shaped rotator or similar.They are build to handle bigger antennas and carry the weight more in a straight line rather than offset like the RS rotators. Then again I probably would never bother to install an antenna small enough to even consider an RS rotator. :laugh: I know someone will pipe up and say they had X antenna up for Y years without an issue but they are lucky. Hundreds of failures and a few good (lucky) installs does not mean they were right.The rotators I have used in the past have been Hygain CD-44, Ham II and at present a Yaesu G-2800DXA waiting to go up.

 

[Zman]

I have had my Hy Gain ham 4 for almost 20 years and to this day it has never failed. It turns a moonraker beam, btw.

 

[Shockwave]

I thought I was pushing my luck with almost 9 feet of mast and the GM above the rotor. After watching in some severe weather I feel a little more comfortable so long as my 1923 chimney holds up. I think that's my weakest link but then again, mother nature has a way of finding weakness we overlook at times. I've also put the GM through a range of VSWR test by placing it in locations one would think cause detrimental interaction. This antenna seems to keep its low VSWR almost regardless of how you mount it (within limits) For example, on a 5 foot mast on the ground has the same VSWR it has installed on the roof.

This was within 15 feet of an aluminum sided building too. If you put this antenna up and don't get a flat VSWR right out of the box, something is seriously wrong because it takes a low to mess this match up. Keep in mind, many of these things mentioned can poorly impact its radiation pattern and performance even though it may not be so evident in the match.

 

[SMILEX2692002]

Thinking about either the Maco Comet or Maco Shooting star. I would tune it for 10 meters. If I could get the swr right on CB with a antenna tuner I would be happy. Since I have never had a directional antenna before I'm sure the Comet would be a nice upgrade from an Imax 2000. Probably even the Y quad would be better than what I have now. I also don't want a huge foot print antenna in the air.
For a rotor I was looking at the Yaesu G-450A. I don't want to get a antenna up on the tower and have a cheap TV antenna rotor break and ruin my antenna.

As for my Imax 2000. Maybe I would mount it on my chimney with a chimney mount.

 

[Shockwave]

The poor performance of the Comet on the vertical side almost makes it just worth putting up a 3 element horizontal. It is quite possibly the most difficult antenna to set the vertical VSWR on. When you manage to get it acceptable, the amount of coax and mast radiation on the vertical side makes the performance just about acceptable if it doesn't plague you with RFI first. Chokes on the coax and mast isolation don't do much at all to help this antenna because we are not dealing with common mode currents. It's parasitic excitation from being right on top of the driven element. In fact, they are so close I'm sure there is some degree of capacitive coupling taking place too. Y Quad or Shooting Star if vertical is important.

 

[SMILEX2692002]

Thanks for the advice. I will avoid that antenna.
I was looking at the price of the Maco M104C vs the Maco M103C. It almost seems better to spend a few more dollars and go with the M104C. As long as the above mentioned Yaesu rotor would handle the load I can't see why not. This will be my first directional beam antenna. I have always used either a Antron 99 or Imax 2000. I have no complaints on either one, just always wanted a beam.

 

[SMILEX2692002]

Picked up a Ham 3 rotor from a local for under $200.00.
Should be all set to use a M103C or M104C with the Imax 2000 on top.

 

[M0GVZ]

Please for the love of god get a rotator cage with a thrust bearing or you'll kill the rotator in no time.

 

[SMILEX2692002]

Please for the love of god get a rotator cage with a thrust bearing or you'll kill the rotator in no time.

My Ham 3 rotors manual says its able to handle a load rating (sq. ft.) of 7.5 when mast mounted. So to not go over 80% of its holding capacity would be to to mount anyting with a surface radius (sq. ft.) of 5.925 or less.

I miscalculated for the Imax 2K and the M104C for my rotor when mast mounted.

Now the M103C and the Imax 2K should stay under the 80% holding capacity of my rotor. The M103C only has a surface radius (sq. ft.) of 4.5 or 60% of the holding capacity. So assuming the Imax dosn't have a surface radius (sq. ft.) of 1.925, I should stay under the 80% threshold.

I agree it would be better to tower mount my rotor and I might end up doing that.

 

[M0GVZ]

You're overlooking the fact that on a 9ft pole in a wind, your Imax will effectively be like you grabbing the end of the pole and pulling it hard to one side.

Not a problem when the rotator isn't moving but when it is it puts undue stress on the rotator on the gears and the motor. Using a thrust bearing transfers that load to the bearing which is designed and rated high enough to take it and cheap enough to be a throwaway item when it fails.

 

[SMILEX2692002]

Can you help me figure out what kind of tower I have so I can look for the right rotor mouting plate?

The tower was here when I bought the house.

 

[W5LZ]

I can't tell you who made your tower but I can tell you it is a 'light duty' tower. I would be careful about how much (weight and wind-loading) you asked it to handle. You need to find out exactly what that top section looks like, it won't withstand much side loading (the center tube thingy).
- 'Doc

 

[Mudfoot]

Looks like standard Dill Tower.

From the angle, it looks like the top has been modified, but probably just the angle.

Call American Tower in Ohio for info.

Or Dxengineering and ask for a rotor shelf that'll fit Dill Tower. Used to be a dude that made plates for Dill and sold them for $20 years ago.

I think Rohn 25 plates fit as well. Also easy to fab one yourself, if'n you got the skills.

 

[Mudfoot]

I have a section of dill tower out back that I can measure the inside distances for you, but I'm pretty sure those dimensions are the same as Rohn 25. I could be wrong, but I'll measure to compare with someone who has Rohn 25, if you wish.

I have seen Dill Tower with different top mast diameters. Mine will accept 2.5" diameter pipe.

 

[SMILEX2692002]

I have a section of dill tower out back that I can measure the inside distances for you, but I'm pretty sure those dimensions are the same as Rohn 25. I could be wrong, but I'll measure to compare with someone who has Rohn 25, if you wish.

I have seen Dill Tower with different top mast diameters. Mine will accept 2.5" diameter pipe.

That would be cool if you can get the measurements. I will measure mine and see what I have tomorrow.