Aligning a Rotator

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VK2HRX
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Aligning a Rotator

Post by VK2HRX » Tue Apr 26, 2016 5:48 pm

Hi Satellite Finder Brains Trust,

I'm refurbishing myAz/El rotators for my 2/70/23 sat yagis and am interested in wether it is the norm to set the rotator to magnetic or true north. So if OrbiSatfinderPlus gives me a bearing is it True or Magnetic ? I appreciate there are a number of Norths that are possible but I am just looking for the convention rather than the most exquisit response.

Compton
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Re: Aligning a Rotator

Post by VK4KHZ » Tue Apr 26, 2016 6:34 pm

All I can offer is the benefit of practical and operational experience...
I have all of my satellite antennas aligned to magnetic north by use of a GPS. This includes my 2395Mhz dish which must track within 3 degrees of the ISS or you get no signal. I consistently obtain excellent results with all of my satellite antennas.

In answer to your question - Magnetic North.

Regards

Shane VK4KHZ

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Re: Aligning a Rotator

Post by VK1JA » Tue Apr 26, 2016 7:19 pm

Hi Crompton,

A little from left field - I align my az and el rotators to the sun or moon. If your tracking software has an option to track the moon then set it tracking the moon and adjust the poles in the rotators so your antenna's point to the moon.

Hope that helps.

Jayson
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Re: Aligning a Rotator

Post by VK2HRX » Tue Apr 26, 2016 7:55 pm

VK1JA wrote:Hi Crompton,

A little from left field - I align my az and el rotators to the sun or moon. If your tracking software has an option to track the moon then set it tracking the moon and adjust the poles in the rotators so your antenna's point to the moon.

Hope that helps.

Jayson
VK1JA
Saves using a compass I guess. Just have to work out how to get me, a spanner and the moon up the ladder on the mast all at the same time.

Good suggestion though, I'll investigate further.
Compton
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Re: Aligning a Rotator

Post by VK2NR » Tue Apr 26, 2016 9:35 pm

Hi Compton,

To keep the answer short, the software will be referencing True North.

For a bit more of an explanation:
Magnetic north is variable depending where you are located on the surface of the Earth - it is simply the direction that a magnetic compass will align. The earths magnetic field is not uniform. Most maps will indicate the number of degrees that magnetic is from True for the area that they cover (called "declination" or "magnetic variation"). In Sydney it is presently +12.57 degrees, meaning that your compass will indicate approximately 12.5 degrees east of True North.

Basically, if I take a magnetic bearing on a station in VK4, his bearing to me won't be exactly 180 degrees from my reading because his magnetic variation will be different to mine - our compasses don't indicate the same direction for north.

It is best to reference True North if possible. That way we are all using the same point of reference.

Regards,
Dave, VK2NR.

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Re: Aligning a Rotator

Post by VK2HRX » Tue Apr 26, 2016 9:49 pm

VK2NR wrote:Hi Compton,

To keep the answer short, the software will be referencing True North.

For a bit more of an explanation:
Magnetic north is variable depending where you are located on the surface of the Earth - it is simply the direction that a magnetic compass will align. The earths magnetic field is not uniform. Most maps will indicate the number of degrees that magnetic is from True for the area that they cover (called "declination" or "magnetic variation"). In Sydney it is presently +12.57 degrees, meaning that your compass will indicate approximately 12.5 degrees east of True North.

Basically, if I take a magnetic bearing on a station in VK4, his bearing to me won't be exactly 180 degrees from my reading because his magnetic variation will be different to mine - our compasses don't indicate the same direction for north.

It is best to reference True North if possible. That way we are all using the same point of reference.

Regards,
Dave, VK2NR.
Thanks Dave. I understand what Mag N is and how it is derived etc. So currenlty I have 1 vote for True, 1 for Mag and 1 for the Moon. Hmmm......
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Re: Aligning a Rotator

Post by VK3DXE » Tue Apr 26, 2016 9:58 pm

THIS!!!
VK2NR wrote:Hi Compton,

To keep the answer short, the software will be referencing True North.

For a bit more of an explanation:
Magnetic north is variable depending where you are located on the surface of the Earth - it is simply the direction that a magnetic compass will align. The earths magnetic field is not uniform. Most maps will indicate the number of degrees that magnetic is from True for the area that they cover (called "declination" or "magnetic variation"). In Sydney it is presently +12.57 degrees, meaning that your compass will indicate approximately 12.5 degrees east of True North.

Basically, if I take a magnetic bearing on a station in VK4, his bearing to me won't be exactly 180 degrees from my reading because his magnetic variation will be different to mine - our compasses don't indicate the same direction for north.

It is best to reference True North if possible. That way we are all using the same point of reference.

Regards,
Dave, VK2NR.
And then this should be spot on:
VK1JA wrote:Hi Crompton,

A little from left field - I align my az and el rotators to the sun or moon. If your tracking software has an option to track the moon then set it tracking the moon and adjust the poles in the rotators so your antenna's point to the moon.

Hope that helps.

Jayson
VK1JA

Because I don't have any obvious geographical features at true north or south, I improvised. I worked out the bearing of the side of my house in relation to true north from the Logger Mapping feature, set the rotator controller to that bearing, then pointed the antenna in the correct direction when tightening everything up. Elevation is simple ;-)

Calibration of rotators is a WHOLE different ballgame. My Yaesu rotator is crap. I have an old Alliance az rotator that needs a bit of a reno, but when last working, maintained 0.5deg accuracy right around the dial. The Yaesu is not as accurate :-(

Once set, it's easy to do a boresite check on your pointing accuracy with the moon. Using the sun hurts, and may lead to premature vision loss.

Using the moon or sun obviously requires ensuring that your location data is as accurate as possible.


Why anybody would use magnetic north as a reference is beyond me. Almost all maps and software reference TRUE north.
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Re: Aligning a Rotator

Post by VK3ALB » Tue Apr 26, 2016 10:20 pm

Whilst in some places magnetic and true north are close it's certainly not the case in NSW where you are.

Choose true north.
Lou - VK3ALB

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Re: Aligning a Rotator

Post by VK4KHZ » Wed Apr 27, 2016 5:38 am

How it was explained to me when I initially set up the tracking software with the AZ/EL rotators is the antennas should be aligned to magnetic north and once your longitude and latitude is input into the tracking software any required correction is made. All of my antennas were set up using this method and they work. I have three of the Yaesu AZ/EL rotators and yes they can be difficult to calibrate - all three behaved differently during the calibration process.
Crompton, I apologise if I have confused the situation but this was not intentional I only offered my comments based on how I set up my satellite tracking antennas and it worked for me.

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Re: Aligning a Rotator

Post by VK2HRX » Wed Apr 27, 2016 7:35 am

VK4KHZ wrote:How it was explained to me when I initially set up the tracking software with the AZ/EL rotators is the antennas should be aligned to magnetic north and once your longitude and latitude is input into the tracking software any required correction is made. .........
Got it, line them up to mag north on the mast and then account for the mag to true variation in the controller. Makes sense.
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Re: Aligning a Rotator

Post by VK2TS » Wed Apr 27, 2016 10:12 am

Rotators should always be aligned to true north as great circle maps and maps generally are always based on true north. Magnetic north slowly varies and from memory at my QTH True North is currently about 11.5 degrees west of north compared to magnetic north. Not hard to orientate with a compass. Your beam headings will then be correct.

This website expalins it: http://www.yourhome.gov.au/passive-design/orientation

Cheers
Attachments
PD-Orientation-TrueNorth-03_fmt.png
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Re: Aligning a Rotator

Post by VK3DXE » Wed Apr 27, 2016 11:13 am

VK2HRX wrote:
VK4KHZ wrote:How it was explained to me when I initially set up the tracking software with the AZ/EL rotators is the antennas should be aligned to magnetic north and once your longitude and latitude is input into the tracking software any required correction is made. .........
Got it, line them up to mag north on the mast and then account for the mag to true variation in the controller. Makes sense.
Why not, if you insist on using magnetic north (and remembering that compasses can be affected nearby metal, magnetic fields, etc.......), make your variation to true north at the rotator when you install it? It really isn't difficult to locate true north and do the job right the first time. There are many, many mapping tools available online and on smart phones, which can all be set to default to true north.
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Re: Aligning a Rotator

Post by VK2HRX » Wed Apr 27, 2016 4:49 pm

Actually, one of my magnetic compasses can be set to read true North, how cool is that!

I am sure I can cope with accounting for the variation.

Biggest issue will be lining up the booms to "north". I was thinking of hanging a string as loops off both ends of the 5m boom of the 23cm antenna and attaching a rod (non Fe) between the string loops and mounting the compass on the rod. Then I can see where the booms are pointed on the ground or there abouts. Then use a pipegripbighammer device to whack the Az rotator mount into the right position, tighten up with chewing gum and Bob's your Uncle.
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Re: Aligning a Rotator

Post by VK3ALB » Wed Apr 27, 2016 4:56 pm

If there is a 23cm beacon (or signal source) at a reasonable distance and you know the direction from your location you can set your rotator to that bearing then use your big hammer to move the beam into the right direction.
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Re: Aligning a Rotator

Post by VK2HRX » Wed Apr 27, 2016 6:04 pm

VK3ALB wrote:If there is a 23cm beacon (or signal source) at a reasonable distance and you know the direction from your location you can set your rotator to that bearing then use your big hammer to move the beam into the right direction.
Yep, the one at Dural. I think I could use that to get max signal and hope that its not bouncing off the neighbors house etc.
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Re: Aligning a Rotator

Post by VK2LK » Sun May 15, 2016 8:11 pm

Suddenly my interest in satellites has been re-kindled...!

What is there to work these days? I recall 10 years ago, AO-51(?) was hammering away and was all the rage..

Also, are there many non- HAM satellites that can be tracked for anything of interest?
Matt, VK2LK

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Re: Aligning a Rotator

Post by VK4CRO » Mon May 16, 2016 6:31 am

Referring to my site plan provided by the Qld government my street runs E-W so I use that as reference ( true Nth)
tnx Cro
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