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Author Topic: Installing a rotor.  (Read 1888 times)
KD5NLV
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Posts: 30




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« on: September 02, 2012, 02:32:33 PM »

Forgive the stupid question, but this is my first antenna instalation. How do I install my rotor so it's aligned with North? Can it be done using the control box after it's in the air? Before I install it in the tower should I make sure the rotor is fully CW or CCW? or does it matter?

And lastly, can I use a simple compass to align to North?

Thank you
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W9GB
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Posts: 2581




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« Reply #1 on: September 02, 2012, 03:25:20 PM »

Antenna (azimuth) rotators in the Northern Hemisphere, have their rotor STOPS at the SOUTH direction.  
The NORTH direction is a smooth sweep from WEST to EAST (or visa-versa).
The PROPER attachment of your directional ANTENNA on the rotor mast -- resolves your concern / question.  
Install the antenna in wrong direction, the rotor indicator is wrong!!


1.  ALWAYS test a rotator and control box, ON THE GROUND, before installing on a tower or mast.

2.  Based on #1, ONCE the indicator is SOUTH, and the rotor is against its stop ---
you can then move the rotor to NORTH (with the control box indicator in agreement).
This step is electronic and you perform with control box, just as if rotor was at top of tower.

3.  MARK the mast (pen, pencil, etc.) that is in the rotor, and install your directional antenna to agree with that directional alignment.

w9gb
« Last Edit: September 02, 2012, 03:28:44 PM by W9GB » Logged
AA4PB
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Posts: 12641




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« Reply #2 on: September 02, 2012, 04:19:29 PM »

You want the antenna to point to "true" North rather than "magnetic" North. You can use a compass but you must add/subtract the appropriate magnetic deviation for your area from the reading in order to convert to the "true" heading. Look at the beam width spec for your antenna to determine how critical the direction is. For example, if your beam width is 30 deg then its not really necessary to worry about the heading down to 1 degree.

For most rotors the North alignment is mechanical rather than any adjustment you can make at the control box after installation. Before installing the antenna, operate the rotor and set it for a North indication on the control box (assuming your rotor is set for center North where the stops are at South). Then mount the antenna so that it faces "true" North and tighten down the clamps.
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KA4POL
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Posts: 1860




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« Reply #3 on: September 02, 2012, 09:45:46 PM »

It is a very good idea to first try the rotor while on the ground. Saves you a second trip to the mast top.
Depending on the place where you live you can use this link http://www.thecompassstore.com/decvar.html to find how to correct your compass reading for true north.
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K7KBN
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Posts: 2754




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« Reply #4 on: September 02, 2012, 09:52:10 PM »

If you're in the Northern Hemisphere:

Go outside on a clear evening and note the position of the North Star (Polaris).  Note the angle it makes with your street, or where a plumb line from Polaris hits the horizon or what you can see.  If you can't locate Polaris, find a nearby Boy Scout...we USED to have to be able to find it. 

That's true north as close as you're going to need it for more than 99% of your hamming career.

Google Earth also will show you where true north is relative to your house and nearby streets, other buildings, etc.
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73
Pat K7KBN
CWO4 USNR Ret.
KA4POL
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Posts: 1860




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« Reply #5 on: September 02, 2012, 10:05:09 PM »

http://www.onr.navy.mil/focus/spacesciences/observingsky/constellations3.htm  Grin
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K7MH
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Posts: 328




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« Reply #6 on: September 02, 2012, 10:34:27 PM »

Quote
Google Earth also will show you where true north is relative to your house and nearby streets, other buildings, etc

And there ya go. it can stay within the KISS method!
Here the avenues run north/south and streets are east/west. As long as you are not in a curved part of an avenue it is pretty easy to judge north since a house is usually squared to the street it is on.
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G3RZP
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Posts: 4326




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« Reply #7 on: September 02, 2012, 11:52:57 PM »

Unless you are going for large VHF beams, the beamwidth is usually wide enough that a few degrees makes no real difference.

If you have the rotor in a cage to give support to the stub mast above the rotor (good idea - takes a lot of strain off the rotor), make sure the bearing is well aligned. Easy way to check this is to measure the current that the rotor draws when you make it turn through 360 degrees - the current should be substantially constant. This is easiest if done on the ground with no antenna.
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K7KBN
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Posts: 2754




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« Reply #8 on: September 03, 2012, 09:09:24 AM »


At times when you can't see Merak and Dubhe, you might be able to pick out Deneb (alpha Cygni - the brightest star in Cygnus the Swan) and zeta Cygni, one of the wingtip stars in that constellation. From zeta through alpha and continue the line about three times its length gets you pretty close to Polaris.
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73
Pat K7KBN
CWO4 USNR Ret.
K8AXW
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Posts: 3598




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« Reply #9 on: September 03, 2012, 09:42:06 AM »

NLV:

First of all I recommend that you have the manual for your rotor handy.  If you don't have a manual, get one.  The manual will save you a lot of grief in setting up, calibrating and operating your rotor.  Not only that if it ever becomes necessary to repair the rotor or control head, you shouldn't have to send it away.

As others have pointed out, wire up the rotor and control and test it out on the work bench or floor.  This way you can watch the meter to see if it twitches or jerks which might indicate a dirty or defective direction wirewound resistor in the rotor.  You want to eliminate a problem before you even think about going out to the tower.  Listen to the rotor....feel it...this way if you have a problem later you'll know what the rotor is supposed to sound and feel like.  I think this would be called familiarity with the gear.

After you run the rotor from stop to stop a few times, rotate the rotor until the meter needle stops on the "N" or "S" which is in the CENTER of the meter.  (This is called either North Centered or South Centered)

Then you can mount the rotor in the tower, making very sure that the rotor shaft is aligned with the tower top bearing as good as you can make it.  Install the beam and while it's still loose, swing it around until it's pointing to the north or the south, depending on rather your meter is North Centered or South Centered.  Be sure you have a gap between the beam center clamp and the tower top bearing.  You don't want the clamp dragging around on top of the bearing.

The beam can be aligned to the north or south with the use of a cheap two-buck compass.  Nothing critical or magical here.  No need to check the stars or planets.... besides nighttime tower work isn't a good idea.   Wink If you want perfection, move the beam accordingly to compensate for the difference between magnetic north and true north.  But even that isn't a big deal.

After this, welcome to the whole new world of DX!  Grin

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AA4PB
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Posts: 12641




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« Reply #10 on: September 03, 2012, 10:24:26 AM »

The difference between magnetic North and true North (declination) varies considerably depending on where you are located. In some locations the difference is only a few degrees which is far less than the beam width of most HF Yagis. If you happend to be on the upper tip of Maine then then true North is 16 degrees west of magnetic North and that could make a noticable difference in antenna heading.
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N6AJR
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Posts: 9879




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« Reply #11 on: September 03, 2012, 01:40:43 PM »

on the ground , test the rotor and turn it to North when done and leave it there Mount it on the tower/ mast /what ever then mount the antenna and point it north.  now the rotor and the antenna are both pointing north.  clamp everything down solid and go have fun.  North can be either true north magnetic north or " I think north is    about there" a long as you know,  is all that matters.  good luck, have fun.
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N7SMI
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Posts: 305




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« Reply #12 on: September 03, 2012, 04:36:32 PM »

The first thing you may want to do is adjust where your stop points are at. For me in Utah I put the stop points at the North (well, one at North and the other at Northeast because my rotator has 90 degrees of overlap). This gives we a full sweep (when turning clockwise) from due North, through the Northeast US, all of the US, the Northwest, Alaska, and all the way back to the Northeast US. Setting the stop points are really more of a convenience than a necessity.

From there, N6AJR's post was spot on. Point the rotator in one direction, mount the antenna, then turn the antenna (or easier, the mast) to align to the same direction. If you're off by a bit, just adjust the arrow on the rotator control a bit to match the antenna direction. This will shift your stop points by that amount, but is much easier than adjusting the entire rotator/antenna system again.
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K7KBN
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Posts: 2754




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« Reply #13 on: September 04, 2012, 09:59:44 AM »

Declination changes over the years.  I dug out my old "Handbook for Boys", the official Boy Scout Manual (1953 edition).  At that time, if you lived close to a line running through Sturgeon Bay WI, northeast Indiana, through central KY and eastern TN, thence along the SC/GA state line, your magnetic compass was very close to true north.
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73
Pat K7KBN
CWO4 USNR Ret.
KC9NVP
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Posts: 64




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« Reply #14 on: September 04, 2012, 10:17:10 AM »

Adjust the Stop Points?  for my two rotors, Hy-gain and Alliance, I ran them thru their rotation and note where they ended in both directions.  I then marked the base with an S for south so that when installing them on the towers, the rotor and control box both agree.  Neither control box have adjustable stops, only meters to show directions.
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