CDE Model Ham M Installation Feedback

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by K8ATG, Apr 16, 2018.

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  1. K8ATG

    K8ATG Ham Member QRZ Page

    I have a CDE Model Ham M rotor that I'm planning installing on my tower. The Ham M was a pretty heavy duty built rotor built back in the 60's and I've serviced it and it's working great. I've got 40 foot of Rohn 25G and have two different ideas I'm debating on as far as installing.

    First, some details.

    1. Tower is Rohn 25G 40 ft. Designed to the 110 MPH wind load rating and guyed at 35 ft.
    2. Rotor is CDE Model Ham M. Manual states it can support exceptional heavy antennas. I don't know the exact ratings. There is no specification in the manual.
    3. Antenna that I'm considering supporting is a JK Navassa-5... 59 lbs and 13.45 sq ft wind rating. (Seems like this rotor will easily handle that).

    Next, my two installation ideas.

    1. I have a 25g top plate designed for mounting a thrust bearing. This would sit on the top of the tower with a thrust bearing installed with approximately a 5 or 10 ft mast running through the thrust bearing to the antenna. The mast would run down about 2.5 or 5 ft below the thrust bearing to a rotor plate that I also have. Therefore, the rotor would sit inside the tower roughly 2.5-5 ft below the thrust bearing mounted in the center of this rotor plate.

    2. Mount the rotor directly on the top plate. Reface the top plate, covering the knockout for the thrust bearing and re drilling the holes (3" centers for rotor) allowing the rotor to rest directly in the center of the top plate but would be supporting the antenna weight both horizontally and vertically. Since the rotor would be on the top plate, the mast would be shortened considerably to decrease the stress on the mast.

    I had always planned for option 1 because the thought of the thrust bearing would reduce stress on the rotor by taking some of the horizontal weight away and allow the rotor to just support the vertical weight of the antenna. After looking at the CDE Model Ham M manual several times, it seems like the rotor was designed to support directional antennas by mounting in-line with the mast. Therefore, I've come up with option 2.

    So, from a experience and recommendation, which do you think is the better option?

    Andrew - K8ATG
  2. WB2WIK

    WB2WIK Platinum Subscriber Platinum Subscriber QRZ Page

    #1 is waaaaaay better.

    If you have an "original" HAM-M, that's nowhere near as robust as the modern HAM-IV/HAM-V series that superseded it over the course of about five decades.

    I would never use a HAM-M without mounting it inside the tower and a thrust bearing above it for a 13 s.f. antenna.

    Use a 2" O.D. mast, for sure (the HAM-M series is designed to rotate concentrically only with a 2-1/16" diameter mast, but 2.00" is usually close enough). Nothing smaller than that, or you'll be scraping up stuff from the ground after a few strong winds.:p
    K8ATG likes this.
  3. K8ATG

    K8ATG Ham Member QRZ Page

    Thanks WIK.
  4. K9STH

    K9STH Platinum Subscriber Volunteer Moderator Platinum Subscriber QRZ Page

    Does your HAM-M have the original "pot metal" ring gear or the newer, replacement, steel ring gear? If it has the original "pot metal" ring gear, do not install the rotor before replacing the ring gear with the newer version. The ring gear is the primary difference between the original HAM-M / Ham II rotors and the newer Ham III and Ham IV. Especially with a larger wind load antenna, the "pot metal" ring gear is put in a high stress level when the rotor is stopped and when there are high winds. The ring gear will definitely break in a relatively short period of time if it is the older type.

    Never even think of putting the rotor on top of the tower! With that type of installation there is a very high moment of force due to the "lever action" from the mast and antenna. Definitely mount it at least 5-feet below the top of the tower. Doing so puts the lion's share of forces on the thrust bearing.

    When installing the thrust bearing, make sure that the weight, of the mast and antenna are on the thrust bearing. Then, all the rotor has to do is to turn the antenna and then hold it in place as the wind blows.

    Glen, K9STH
    K8ATG likes this.
  5. K8ATG

    K8ATG Ham Member QRZ Page

    I would suspect that it is the older ring gear. I'll open it back up and take a look. If it is, I'll replace it with the stainless steel one.


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