Daily Archives: June 12, 2011

Rotator control

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One of the benefits of having a tower is that, for bands with shorter/smaller wavelengths, I can use directional antennas.  That means that the radiated energy goes more toward one direction than another.  You can point it.

But to do the pointing you have to have some kind of motor that does the moving.  My system has a rotator that will turn my antennas relative to the points of the compass (azimuth).  I do not have any mechanism for moving “up and down” in elevation.  (If I were tracking a satellite or the moon I would want to be able to do that.  But I’m not.)

Why only those antennas for smaller wavelengths?  Because longer wavelengths mean larger antennas.  Shorter wavelengths mean smaller antennas and more pointable antennas.  As frequency goes up the wavelength gets shorter.  So for higher frequencies you have smaller antennas.  (Which is why your cell phone uses a very high frequency.)

I have a set of wires that run from the house to the rotator on top of the tower.  They carry electrical power to the motor and they also carry sensing information to tell me which direction my antenna is pointing.

This picture is of the control box.  There is an on/off switch, a calibration knob (only used at the beginning to get N to be north.)  and three buttons.  The middle button releases a mechanical brake.  The other two are to move the motor clockwise or counter-clockwise.  To operate you hold down the brake button while also pushing a motor-direction button.  Release the motor button while still holding down the brake release.  After 4-5 seconds you can then release the brake button, which sets the brake again.

And there is a meter which is used to tell me which way my antenna is pointing.  As you can see, to get from SE to SW I have to go all the way around via N.  I cannot go past S.  My rotor probably could be made to do it, but my antenna feed wires would eventually wrap around the mast and make a mess.  So they make the rotor only go so far.

(and yes, I need to get a camera with a close focus ability…)

 

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Jun 12, 2011
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