[amsat-bb] Re: Mounting antennas on a tower
jkopala at gmail.com
Sun Sep 23 15:32:04 PDT 2007
Here is another approach to the problem.
1. You need a rotor base plate that can be mounted at any level in the
tower. Basically, it should rest on and be secured to the cross braces
between the tower legs.
2. Next use a thrust bearing at the top of the tower.
3. Your mast needs to be heavy enough to withstand whatever winds you may
encounter from storms when extended several feet beyond the top of the
tower. At least half of the mast will remain in the tower.
4. The mast can be positioned vertically within the tower using a pulley at
the top of the tower and a rope secured to the mast near the base. Helpers
on the ground use the rope to raise and lower the mast while a person on the
tower guides and secures the mast at the desired height using the thrust
5. You then attach the elevation rotor with its cross boom and antennas in
as many steps as required to do so.
6. Using the rope to control the mast height, loosen the thrust bearing
screws and raise the entire structure so that the satellite antennas have
the necessary clearance above the HF beam.
7. Secure the thrust bearing screws and attach the HF beam.
8. Again raise the mast so that he HF antenna is at the desired height plus
about 1 foot and secure it in place.
9. Attach the rotor base and rotor to the tower just below the base of the
10. Lower the mast to the top of the rotor and secure it in place.
That is how I set up my current HF installation. Rather than having a
satellite setup on top, I have an Cushcraft R-7 vertical which extends
another 22 feet above the top of the mast and is spaced about 5 feet above
my triband beam. You can put anything up there you want. I was not
thinking satellites when I set this up many years ago, so my satellite
antennas are on a roof mount.
I prefer center mounted antennas because I can mechanically balance the
entire antenna system. I have balanced it front to back, side to side, and
up and down. Basically I mount my antennas on a fiberglass cross boom and
adjust the antenna positions (with coax attached) so that the whole setup is
balanced front to back. Then I use another pipe and clamps to determine the
rotor position so that the setup is balanced from side to side. Finally, I
mount the heaviest antenna on the bottom side of the crossboom and the
remaining antennas on the top side to further eliminate imbalance as the
antennas rotate vertically. The idea is to minimize the stress on the rotor
gears and bearings. Ideally, the rotor is not lifting or supporting any
extra weight when it moves the antennas. The antenna structure could be
moved with one finger if the rotor was not holding it in place. With end
mounted antennas, the rotor brake and gears must support and lift the
entire weight of the antennas every time the antenna elevation changes.
I'll also send you a picture of my current satellite setup. This is NOT the
ideal setup because the rotor is not mounted in a tower section and there is
no lateral support above the rotor for the mast. But it does give you a
look at a setup with center mounted antennas on a cross boom with an
elevation rotor all mounted above a 6 meter beam. The satellite antennas do
rotate a full 180 degrees of elevation and clear the 6 meter beam. The
longest antenna is an old KLM 2 meter circular polarized antenna that is 12
feet in length. Note that with the cables attached, the balance points move
somewhat toward the rear of the antennas. Also, note the preamps just below
the azimuth rotor.
And DON'T FORGET the preamps.
----- Original Message -----
From: "Eric Christensen" <eric at christensenplace.us>
To: "AMSAT-BB" <amsat-bb at amsat.org>
Sent: Friday, September 21, 2007 7:03 PM
Subject: [amsat-bb] Mounting antennas on a tower
> I'm contemplating antennas and a tower at the new homestead and I have a
> If I can figure out how to mount an elevation rotator at the top of a
> pole and have the azimuth rotator rotating said pole from the tower
> would I have any problems with putting a small HF tri-band beam on the
> pole, below the elevation rotator, and then mount all my satellite
> antennas to the elevation rotator's pole? Has anyone done a combination
> like this?
> Eric Christensen, W4OTN
> AMSAT Area Coordinator - Southeastern Virginia USA
> AMSAT Member 35360
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