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### Topic: Point an antenna at a static GPS location (Read 4018 times)previous topic - next topic

#### Receo

##### Aug 23, 2013, 04:19 am
Hello folks,
I'm setting a goal for myself to build a device that will point a small antenna to a known GPS location (lat,long,alt)

My antenna will never be more than 12 miles from the known GPS location.
I will need to move my antenna project every couple of months within my 12 mile radius but it will always point back to my known gps location.

Regarding hardware,
I believe I will need:
arduino (which one not a clue) GPS shield (recommendations appreciated )and two servos.
Possibly an electronic compass.

This will be my first arduino project
If you could provide any direction it would be greatly appreciated.

#### Robin2

#1
##### Aug 23, 2013, 07:46 am
Why?

...R
Two or three hours spent thinking and reading documentation solves most programming problems.

#### AWOL

#2
##### Aug 23, 2013, 08:50 am
The TinyGPS library has a "course_to" method.
"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.
Do not send technical questions via personal messaging - they will be ignored.

#### Nick_Pyner

#3
##### Aug 23, 2013, 09:08 am
I don't believe you will need a compass. An on-board GPS is there to determine one position and a the other position is static by definition. You can therefore calculate altitude and azimuth for the antenna, and I guess the GPS can do that chore for you.

#### Grumpy_Mike

#4
##### Aug 23, 2013, 09:20 am
This is the sort of project that radio hams do. You could try looking at some web sites for built examples of this.
You would not use a servo and controlling tha azimuth is unnecessary.

#### Shpaget

#5
##### Aug 23, 2013, 09:36 am

I don't believe you will need a compass. An on-board GPS is there to determine one position and a the other position is static by definition. You can therefore calculate altitude and azimuth for the antenna, and I guess the GPS can do that chore for you.

But the device does not know its own orientation just from the GPS location.

It seems to me that a simple map and compass with manual orientation would be much simpler, more portable, sturdier and faster. Once in a few months is really not that often for such a simple operation.
Other than that, Grumpy's suggestion of radio beacon seems a lot easier (think low power NDB).

How accurate your antenna pointing has to be?
What kind of terrain is in your 12 mile radius (hills, plains, urban, rural etc)?
Will you be positioning your antenna somewhere in the wilderness, out in the open or in a building?

#### Nick_Pyner

#6
##### Aug 23, 2013, 09:41 am

But the device does not know its own orientation just from the GPS location.

Yes........

#### Grumpy_Mike

#7
##### Aug 23, 2013, 10:06 am
How?
A GPS only returns lat and long. You can only get a heading if you are moving. When you are static ther is no way of telling where you are pointing.

#### 123Splat

#8
##### Aug 23, 2013, 08:14 pm
Mike,

With all respect, oh great one, oh, yes they do.  You get a reasonablly accurate 'course direction', with respect to either magnetic, or true, north after warmup and reception of three or more satalites.  With earlier modules, your direction got better with movement. But now days, with the multiple channels, you are pretty good from the get go (at least here in the states).

#### Robin2

#9
##### Aug 23, 2013, 08:38 pm
So if you sit a GPS receiver on a table in your garden and rotate the receiver about its own centre it will be able to tell you which new direction it is pointing?

...R
Two or three hours spent thinking and reading documentation solves most programming problems.

#### 123Splat

#10
##### Aug 23, 2013, 09:21 pm
Mine do, with better response than my E-Trek handhelds.

#### el_supremo

#11
##### Aug 23, 2013, 10:26 pm
This site has a formula for the bearing which is basically all you need:
http://www.movable-type.co.uk/scripts/latlong.html
It gives the general formula for the bearing from one lat/long to another. In your case, if the second one is always the same, the formula simplifies a bit.
But if you only move the antenna once every few months you could easily do the computation of the bearing on a calculator (or Excel spreadsheet), point the antenna and you're done.

Pete

#### wizdum

#12
##### Aug 23, 2013, 11:15 pm

Mine do, with better response than my E-Trek handhelds.

I suspect that this is due to the manufacturer adding in an analog or digital compass, NOT because GPS tech got better. GPS only gives you a single point, it has no idea of direction until you move. Even then, GPS accuracy can be all over the place depending on cloud or tree cover.
"Anyone who isn't confused really doesn't understand the situation."

Electronic props for Airsoft, paintball, and laser tag -> www.nightscapetech.com

#### Chagrin

#13
##### Aug 23, 2013, 11:59 pm
1) Mark your antenna platform with a 360o compass.
2) With a GPS on the platform, move ~10 meters in any direction in a straight line, and note the GPS's reported course heading.

...and that's it.

#### kg4wsv

#14
##### Aug 24, 2013, 01:06 am
Quote
With all respect, oh great one, oh, yes they do.  You get a reasonablly accurate 'course direction', with respect to either magnetic, or true, north after warmup and reception of three or more satalites.

Wrong!

The GPS knows the course if it is moving.  If it isn't moving, it doesn't know.  Some units immediately revert to a course of 0, some hold their last estimate of the course.

If you want to know orientation when stationary, you need a compass.

-j

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