how to calibrate your beam heading.

[VK5PJ]

I have been pondering of late how I will accurately set the headings of my yagi's on the tower. In the past I have used a compas and a fudge factor to set north (yes I know its not good.) I even have used the moon as a calibration point for tests but it keeps on moving

In 2006 I bought a cheap GARMIN GPS that has the basic navigation functions (it also displays your location in Maidenhead if needed) so I am planning on going to a nearby hill (2 Km away that has a trig marker on it) and putting that in as a marker point, then come back to the base of the tower and get the GPS to tell me what the heading is to that hill. From here I should be able to point the yagi's at the hill and then alter the rotator to ensure it matches the bearing on the GPS.

hopefully this will give me a repeatable alignment point for the future

Anyone else tried this, is my reasoning flawed?

[VK4GHZ]

Small B&W CCD cameras are dirt cheap these days.
I was thinking of mounting one on the boom of the yagi, then using a monitor in the shack, for visual checking.
Feed +5V up the 75ohm coax for the camera power.

That way, during daylight hours (or the moon at night), knowing where the other "object" is (from GPS co-ords), you could calibrate where your pointing, and have visual confirmation.

If not on the boom itself (would it cause a problem?) then in the same alignment on the pole above/below the yagi.

Maybe at the reflector end, pointed backwards, to minimise any undesirable interaction.
Just add/subtract 180°.

[VK2KRR]

Peter your method sounds good to me.
You could try and check this with WSJT beam heading calculation of the rising or setting sun (JT65) and see where you get maximum sun noise. Then your moon pointing should be OK and any other heading you choose.
Ive done this a few times with my antennas here to check the rotator setting are right.

[VK7JG]

Hi Peter .
Just read Leigh's reply .
I also use WSJT for my beam headding calibration .
When the moon or sun is low down align your beam by standing behind it and using line of sight for alignment . Once it is spot on if you have an OzSpid rotator you can calibrate it from the front panel . Otherwise set you rotator indicator to what the WSJT says it should be and align your beam accordingly.

73
Joe
VK7JG

[VK2OMD]

Anyone else tried this, is my reasoning flawed?

Peter,

Try this:

Initially:

1. Find your magnetic offset;

2. Locate a point using a compass and that is a convenient walking distance from your antenna that allows a clear sight to and along the antenna boom and that is some convenient angle wrt true north.

3. Subtly make a permanent mark at this point that you can return to in future without the compass, and write down the bearing to the point (180 less than the true bearing of the corrected compass shot) someplace convenient.

(You will achieve better accuracy looking back to the boom from 50m - 100m away, than looking along the line of an overhead boom.)

From time to time:

Send a reliable observer to the point established above and adjust your antenna until the observer sights straight along the beam, note / correct the offset of the controller indication from the known bearing to the point. You may need a radio or phone to communicate with the observer.

I won't make any sexist comments, but note that I said a reliable observer.

This is a procedure for calibrating the boom alignment, it does not deal with pattern skew.

Owen

[VK2JDS]

yes Owens technique is good , its what i use for beam heading sighting for 1296 with the 3 metre dish.

to get a heading on a station say for example vk2dag on the coast for 1296.150, i use a road atlas main page, from north of bathurst i put the straight edge of a silva plastic orienteering compass from home to ourimba, then align the red lines under the swivelling part of the compass towards north on the map . now rotate the dial 11 degrees clockwise and it should be right.

take your compass and stand in front of your antennas (with the power off)
sight back to the feedpoint, line yourself up with your array and align the red end of the needle to the main red pointer of the base. works well and is within a few degrees.
its enough to get a good bearing to chainsaw your way through brush and trees to set up a path and unless you have a liason channel on 2metres you wont get a contact on 23cm.
73's

[VK4ADC]

Minor change to Owen VK1OD's method.

Use the long shadow from the early morning or late afternoon sun of the yagi's supporting tower / pipe masting plus the Sun's astronomical data from the WSJT software at that point in time to put a convenient mark along your boundary line. Repeat for every supporting mast when its shadow reaches the eastern or western property boundary ...

Todays' afternoon sun was at 260 degrees (+/- 0.5 degree) at about 5PM (value from WSJT) so the centre of the long shadow point was marked at ( 260 - 180 = ) 80 degrees (ref True North). I marked the fence rail with a permanent mark including the 80 degree calibration value.

I can now preset the rotator controller to 80 degrees, then mechanically point the array at the permanent mark - and for the first time in some years, it will actually be accurately pointing in the correct direction ! { and no magnetic compass or declination (magnetic variation) values involved while tower-topping }

73 Doug VK4ADC

[VK2OMD]

Minor change to Owen VK1OD's method.

Use the ...

Doug, in the absence of simple equipment like a reliable accurate compass, there are all sorts of other solutions.

I guess it is easy to take for granted that most people have a compass, but they probably don't. Just as it seems lots of people don't know their lat/lon.

My suggestion is that whatever is done,

• the sight is taken from sufficient distance to get a clear sight along the boom, a sight that is sensitive to pointing error; and
  that some sort of cross check is performed to expose gross error (like using the wrong sign for magnetic variation, putting the wrong longitude into WSJT, etc).

Google earth or a paper map are potential sources of good bearings to a local feature that can be lined up behind the mast for a known bearing, but preferably one that lines up with calibration marks on the rotator indicator where that improves accuracy.

A known shadow bearing may be useful... but if it is cast into neighbours yards, it may be inaccessible at good distance, or indistinct at good distance.

Simplest is best, and each OM needs to devise something suited to their own neighbourhood, and the ideas put here might give some inspiration.

Given the rate at which I hear people complain about indicators getting out of cal (rotator clamps slipping, boom clamps slipping, rotator / indicator internal issues etc), I can see a certain merit in the camera option described by one respondent. Perhaps we could compensate for sloppy installations by putting an electronic magnetic compass sensor on each boom and selecting the appropriate sensor for display! There is a project.

Owen

[VK3SIX]

I am lucky the grid streets run true north south.
My driveway is exactly true east west.
And i can check it from outer space to prove it.

I also own a GPS430 in my aircraft and can run it in simulator mode at home on the PC and get approach accuracy using RAIM of 1/10 of 0.6 nM resolution (1.32 KM)
or 100 M.

GPS RX offsets the magnetic variation automaticcally and applies it to the aircraft track so it matches near the radio track.



The reality is for 6M EME the best yagi (11 el M2) are only +/- 12 degrees.

I have no trouble pointing the antenna at the moon or anywhere else.

Thats the difference between true CW eme where you listen and this WJST PC generated stuff which you watch.

After all these years with an M2 Peter surely you know where its pointing?

They are sharp but not that sharp.
if I swing it on VK5 I can home in accurately on your beacon every time.

How about a preset rotator with memory stop spots?

Adams camera a good idea porviding you can wx proof it.




And remember paths are not always straight lines on 6M at least.

Magnetic variation when using a compass.





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