[TowerTalk] north

Fri Dec 26 14:18:50 EST 2014

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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>>
>>
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