What is the recommended mast size-diameter for the Rotator/Rotor CM-9521A & CM-9521HD?


CM-9521A & CM-9521HD Mast Size, and Weight Specifications;
We really do not have a maximum weight specification for the CM9521A rotator.

  • The rotators were designed for antennas weighing ~15lbs to 30lbs along with a 3ft long upper mast.
    • Like many products, we're sure it was over-designed to handle more, but installing something other than ~15lb to 30lb antenna and an upper mast longer than 3ft, may shorten the life...
    • We still have many 25 year old rotators out in the field working fine with 1 or 2, 15 lb antennas on them. 
      • However, the maximum balanced wind load antenna projected area cannot exceed 3sq ft. Additional details on this are below.
  • The upper mast clamps can accept from 1" to a 1 7/8" pipe
    • If you are going to run the upper mast through an upper stabilizing sleeve on a tower, the upper mast must be 1 1/4" diameter in order to rotate "true". (Centered in the upper mast mount.)
      • See Fig 2 on page 5 of the CM-9521A Instruction sheet for an example image. 
    • If you use smaller or larger diameter than 1 1/4", it could seize as it rotates.
    • If you are not going to run the upper mast through a sleeve, then the diameter is not as important.
  • The lower drive unit mast clamps can accommodate from 1", up to ~1 7/8" to 2".
  • Also, make certain that you do not have an upper mast over 3ft tall.
    • Too tall of upper mast creates excessive leverage in windy situations and can wear on or damage the thrust bearing assembly and upper mount shim bushing.
    • Your mast could be damaged by high winds if it is longer than 3ft or if the antenna 'Wind Load projected area', is larger than 3sq ft.
    • All of Channel Master's outdoor antennas 'wind load projected area' are less than 3 sq ft, and can be used with the CM-9521A & CM-9521HD rotator systems. 
    • As an example, the antenna with the highest 'wind load projected area is our CM-4228HD, with a wind load projected area of 2.14 sq ft.
    • Our largest/~100 mile Log periodic/Yagi antennas, 'wind load projected area' are less than 2 sq ft.

You can find the CM-9521A and CM-9521HD installation instructions here

You can find troubleshooting tips here

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