[TowerTalk] north

Don w7wll at arrl.net
Fri Dec 26 15:17:52 EST 2014 

Wife suggested giving the compass to Goodwill and buying a dog. Smart alec. 
Been there done that, retired the scooper.

Kidding aside, sometimes where we have the yagi pointed is important. A few 
or more degrees from her to VU is not cause for alarm, but on 10 with more 
elements, perhaps it is more important for working the close in low strength 
new county in CO.

I've obviously missed earlier discussion on the owl. I see a few refs to N. 
What am I missing?

-----Original Message----- 
From: Bill Aycock
Sent: Friday, December 26, 2014 11:23 AM
To: Gary - AB9M ; towertalk at contesting.com
Subject: Re: [TowerTalk] north

I think the best thing I learned from this cycle was the straight poop about
the Dog alignment method.
Bill--W4BSG

-----Original Message----- 
From: Gary - AB9M
Sent: Friday, December 26, 2014 1:12 PM
To: towertalk at contesting.com
Subject: Re: [TowerTalk] north

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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