[TowerTalk] north

Sat Dec 27 13:14:37 EST 2014

Why not place a nonconducting pointer(PVC pipe?) on the top of the tower 
pointing north and subsequently align the boom with the pointer?

At least for non-rotating towers.

Patrick   NJ5G

On 12/26/2014 1:18 PM, Larry Loen wrote:
> I don't understand all the naysaying here.
>
> If we can get our rotators aligned with in 1 degree, 5 degrees, 1/2 a
> degree accuracy, depending on our stamina and ability to understand the
> procedure, we should.  If we don't care, we can take the consequences of
> whatever error we accept.
>
> It's a "one time cost" on the whole (not a lot of maintenance on this).
> Moreover, you can lay it out in such as way as to have some sort of "line"
> that preserves the effort, making maintenance even less of an issue.
>
> No matter how wide the beam width of your antenna, a more accurate
> north/south placement reduces the inevitable _added error_ of not having a
> perfect N/S alignment of your system.  If you were off by, say, 20 degrees,
> this added error would be obvious and it would be obvious that it is
> additive to boot.  If you are off by 5 degrees, it is less obvious, but it
> is still an error and it is still additional.
>
>
> Larry WO7R
>
> On Fri, Dec 26, 2014 at 12:12 PM, Gary - AB9M <glhuber at msn.com> wrote:
>
>> My response with the link to FM 6-50, was as I explained to one here who
>> contacted me directly, was done with tongue firmly planted in my cheek. I
>> know the process well, but use the generally North running road in front of
>> my house to get an approximate North for my rotor. I just wanted to see
>> what would happen if I turned the precision factor up by say a factor of
>> ten.
>>
>> Happy New Year everyone.... "now beaming over the North pole"
>>
>>
>> 73 & DX,
>>
>> Gary - AB9M
>>
>> -----Original Message----- From: Gary - AB9M
>> Sent: Thursday, December 25, 2014 10:50 AM
>> To: towertalk at contesting.com
>> Subject: Re: [TowerTalk] north
>>
>> For greater precision, say about 0.33 degrees use the Polaris - Kochab
>> method as explained in US ARMY FM 6-50
>> (http://www.globalsecurity.org/military/library/policy/
>> army/fm/6-50/Ch5.htm).
>> Many years ago, I used the Polaris - Kochab method for directional control,
>> first finding True North, then the Direction of Fire, to align Howitzers,
>> for the precision flying (in an arc) of thirty-five pound projectiles.
>>
>> Once you get the telescope properly aligned by Polaris - Kochab, you only
>> have to lower it verticly to the ground. The line from the telescope to the
>> sighted spot on the ground is to True North.
>>
>>
>> 73 & DX,
>>
>> Gary - AB9M
>> -----Original Message----- From: Patrick Greenlee
>> Sent: Thursday, December 25, 2014 9:55 AM
>> To: towertalk at contesting.com
>> Subject: Re: [TowerTalk] north
>>
>> Ahh, what fun.  Be careful shaving Phill as he gets razor rash easily.
>> I too am a bit into astrophotography and a little star gazing with or
>> without my ancient Celestron Pacific 8 inch reflector.  I also dabbled
>> in using a sextant for navigating back in my sailing days.  Was maritime
>> mobile for 9
>> years.
>>
>> You can get local noon on dry land with a sextant and a bowl of water as
>> a horizontal reflecting plane.  you can get a very precise local noon
>> and south. By taking a series of sights prior to, near, and after local
>> noon you can deduce the time and direction of local noon to an arbitrary
>> accuracy dependent on your observing conditions and skill taking the
>> sights.  It is quite easy and you don't need published tables of data or
>> an expensive instrument.  A cheap plastic sextant will git 'er done
>> better than you need for aiming antennas.
>>
>> I personally favor a vertical rod driven in the ground and checked
>> carefully for verticallity.  I put small pins in the ground where the
>> tip of the shadow is at any given time.  The series of stakes mark a
>> smooth curve with equal periods of time indicated on either side by
>> equal distances and it easy to see the point where the shadow is
>> centered (also longest shadow.)  This is true north from the vertical
>> rod (gnomon.  The shadow cast by the gnomon has two shades of gray, the
>> umbra and penumbra.  This finite width is NOT a problem, just use the
>> center of the shadow.  The shadow width is a function of the rod width
>> and the fact that the sun is not a point source. In practice neither
>> matter much as it is easy to determined the center of the shadow cast by
>> the gnomon.
>>
>> This thread inspires an experiment.  I will use a non conductive
>> (plastic) dodad attached to the antenna directly above the mast and plot
>> its shadow position with small stakes starting before and running past
>> noon, as per clock time to ensure I start before and continue past local
>> noon far enough to give an interpretable curve. I can then easily find
>> the location of the shadow at local noon and drive a permanent stake.
>> Thereafter sighting through the center of the tower to that permanent
>> stake will give me a true north reference.
>>
>> All caveats listed below are given due consideration.
>>
>> No ground hogs will be inconvenienced by this endeavor.
>>
>> Patrick    NJ5G
>>
>>
>>
>>
>> On 12/25/2014 7:31 AM, Jim Lux wrote:
>>
>>> On 12/24/14 10:39 PM, Spencer wrote:
>>>
>>>> In the northern hemisphere,  the shadow of a vertical object at solar
>>>> noon will point north.
>>>>
>>>>
>>> I've done all these North finding techniques over the years as kind of a
>>> hobby activity (and sometimes professionally, too)
>>>
>>>
>>> In mid-latitudes the shadow and stick works fairly well, although it's
>>> hard to get sub-degree precision (for your North facing owl?) because of
>>> several reasons:
>>> 1) The stick has to be vertical to within the accuracy of your desired
>>> measurement.
>>> 2) the sun is half a degree wide, so the shadow edges are indistinct
>>> (you could check this in a few weeks, if you shave the groundhog first,
>>> so the fur doesn't cause the indistinct edge)
>>> 3) the sun moves pretty fast, so it's hard to tell the exact instant of
>>> solar noon.  The earth turns a degree in 4 minutes.  Of course, you don't
>>> need a precisely aligned antenna to receive WWV, and, knowing your
>>> longitude, you can calculate when solar noon is. (don't forget the
>>> "equation of time")
>>> 4) the shadow is pretty short at noon unless you're well north (in the
>>> summer).
>>>
>>>
>>> At 34 degrees north, in the summer (prime tower building season), the
>>> shadow is pretty short. The sun's only 10 degrees from vertical at the
>>> solstice.  At La Paz or Los Cabos, Baja California, on the solstice, the
>>> sun is directly overhead at noon (or so close you won't be able to easily
>>> tell the difference)
>>>
>>> It's MUCH easier to get north if you mark the shadow periodically. You'll
>>> get a curve that you can then use to determine north.
>>>
>>> What you do is make a smooth curve of shadow position during the day.
>>> Then, you take a string from the *top* of the stick and scribe a semi
>>> circle across the curve of constant radius.  Draw a line between the two
>>> intersections of curve and semicircle.  The perpendicular bisector of that
>>> line faces north/south.
>>>
>>> (you still have the 1/2 degree width of the sun to contend with, and the
>>> ground has to be level within a fraction of a degree, etc.)
>>>
>>>
>>>
>>> If you're "between the tropics" (of Cancer and Capricorn) the shadow goes
>>> both north and south, depending on the time of year. Think of a stick on
>>> the equator: from March equinox to September equinox, the sun goes north,
>>> so the shadow is south, and from September to March, the sun goes south.
>>>
>>> And for hams aligning their rotor in midwinter in the far north? No
>>> shadow at all.
>>>
>>> By the way, the north star (Polaris) is about 3/4 degree from true north.
>>> It moves around the true pole in a circle. You can look up the position at
>>> a given time/date, or watch it in a telescope and look for culmination.
>>>
>>>
>>> Moral of the story:  getting true "north" to even one degree accuracy is
>>> harder than it seems at first glance.
>>>
>>>
>>>
>>> _______________________________________________
>>>
>>>
>>>
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>>> TowerTalk at contesting.com
>>> http://lists.contesting.com/mailman/listinfo/towertalk
>>>
>>>
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