Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

   Home   Help Search  
Pages: [1]   Go Down
  Print  
Author Topic: Pointing very narrow beam yagis, or is it your inclination to use declination?  (Read 2259 times)
K9ZF
Member

Posts: 76


WWW

Ignore
« on: March 04, 2014, 12:42:32 PM »

Greetings group,

I am in the process of "rebuilding" my station.  I've been inactive for the past few years but am trying to turn things around.  I am primarily a VHF/UHF contester / DXer.

I haven't given it much thought in the past, mainly because the antennas I used had fairly wide beam widths.  However, now that I am rebuilding my station I am putting up some fairly long boom yagis with  a narrow beam.  So, it would seem to be important to be spot on when pointing the antennas.

So what I done was look up my magnetic declination (difference between true north and magnetic north) and offset my rotator 5 degrees.  (my declination was 4*43'...)

What do you think?  Did I do it right?  Is it worth bothering with, or just stick to the compass?  So, when I am on http://www.on4kst.org/chat/ and it tells me the other station is 151 degrees, will I be pointed correctly?     How did you do it at your station?

Thanks & 73,
Dan

--
K9ZF
Amateur Radio Emergency Service, Clark County Indiana. EM78el
Once and future, K9ZF /R no budget Rover ***QRP-l #1269
Check out the Rover Resource Page at:
<http://www.qsl.net/n9rla>
List Administrator for: InHam+grid-loc+ham-books
Ask me how to join the Indiana Ham Mailing list!
Logged

--
K9ZF
Amateur Radio Emergency Service, Clark County Indiana. EM78el
The once and future K9ZF /R no budget Rover
 ***QRP-l #1269
Check out the Rover Resource Page at:
<http://www.qsl.net/n9rla>
List Administrator for: InHam+grid-loc+ham-books
Ask me how to join the Indiana Ham Maili
AA4PB
Member

Posts: 12770




Ignore
« Reply #1 on: March 04, 2014, 12:59:13 PM »

True North is what you want to use rather than magnetic North (i.e. the compass reading). In most cases it doesn't make that much difference but it's just as easy to do it correctly as not  Wink
Logged
W1VT
Member

Posts: 821




Ignore
« Reply #2 on: March 04, 2014, 01:49:27 PM »

A hiking GPS will typically give you the option of using magnetic North instead of true North when calculating beam headings.

I've used a compass with great success in working 10GHz troposcatter DX.  In New England, the magnetic variation is much larger than the beam width of 2' dish, making it essential to factor it in properly.

I'd suggest using Polaris or the Pole star at night to verify that your beams are accurately pointed.

Zack W1VT
Logged
WB6BYU
Member

Posts: 13117




Ignore
« Reply #3 on: March 04, 2014, 02:06:22 PM »

Quote from: K9ZF

... offset my rotator 5 degrees.  (my declination was 4*43'...)

What do you think?  Did I do it right?  ...




That depends, of course, which way you corrected your rotator display.
If you go the wrong way relative to your magnetic declination (which could be
either + or -) then you'll be 10 degrees off instead.

Does it make a difference?  Depends - what is the half power beamwidth of
your antenna array?  If it only varies 1dB in 5 degrees, then perhaps not
enough to worry about.  You may still have to swing the beam back and forth
a bit to find the best signal, as they might not always arrive exactly where you
would expect.

The declination correction depends greatly on your location:  here on the West
coast it can be 16 to 17 degrees, and up in Southeast Alaska it was over 30 degrees.
And the declination shifts with time:  in fact, the rate of change has increased over
the last 20 years or so.

How do you check?  The North Star is one way.  I lived on a street that ran due
North/South, so basically pointed it up the street (if your antenna is, say, 50' from
the edge of the street, sight it on a point as far up the street as you can see that
is also about 50' from the edge.  The required accuracy of that distance estimate
decreases as you go further away.)

Or look choose a landmark that you can see and measure the angle to it from a map,
then use that for your calibration point.  Or calculate the bearing (either from the map,
from lat and long, or using a GPS) to a ham friend's house, then have him transmit and
turn your antenna for a peak to see how close your calibration is.

There are lots of other ways, too.  The simple declination correction should be the
easiest, as long as you apply it in the proper direction.
Logged
K4SAV
Member

Posts: 1834




Ignore
« Reply #4 on: March 04, 2014, 04:29:38 PM »

Aligning antennas at night isn't much fun.  Here is the method I use:

To find true north, go to
http://aa.usno.navy.mil/data/docs/AltAz.php
and enter your coordinates in Form B

Look at the data returned and get the time when the sun's azimuth is 180 degrees.  At that time, go out and find the point on the ground where the top of the tower casts its shadow on the ground.  Put a stake there.  Line up the tower with the stake and that will be true north.

... Unless of course, if you happen to be far enough south that the sun passes to your north, in which case you have to use 0 degrees instead of 180.

Jerry, K4SAV
Logged
KI6LZ
Member

Posts: 579




Ignore
« Reply #5 on: March 04, 2014, 05:01:38 PM »

Here's my easy way using DX Atlas:

I pick an alignment point which is easy align to. My roof top edge is easy to align my beam parallel to.

I initially zoom in on the sun in DX Atlas and using the bearing cursor click on the sun. I do this around noon and wait until the tower shadow is perpendicular to the roof edge, then note the bearing angle. In the northern hemisphere the shadow is 180 degrees out from the true bearing. Then I know the true bearing of the beam when it is perpendicular to my roof line. Voila.

The deviation is about 14 degrees here. I find this more than close enough for my HF Yagis. No need to get spun around trying to figure out which direction the deviation either subtracts or adds to magnetic.


Logged
K9ZF
Member

Posts: 76


WWW

Ignore
« Reply #6 on: March 05, 2014, 06:52:28 PM »

Thanks for the tips guys!!

73
Dan

--
K9ZF
Amateur Radio Emergency Service, Clark County Indiana. EM78el
Once and future, K9ZF /R no budget Rover ***QRP-l #1269
Check out the Rover Resource Page at:
<http://www.qsl.net/n9rla>
List Administrator for: InHam+grid-loc+ham-books
Ask me how to join the Indiana Ham Mailing list!
Logged

--
K9ZF
Amateur Radio Emergency Service, Clark County Indiana. EM78el
The once and future K9ZF /R no budget Rover
 ***QRP-l #1269
Check out the Rover Resource Page at:
<http://www.qsl.net/n9rla>
List Administrator for: InHam+grid-loc+ham-books
Ask me how to join the Indiana Ham Maili
Pages: [1]   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!