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Re: How to calibrate the azimuth angle?



----- Original Message -----
From: "Chiu-Teng Tsai" <n2693415@mail.ncku.edu.tw>
To: <amsat-bb@amsat.org>
Sent: Thursday, December 27, 2007 6:08 AM
Subject: [amsat-bb] How to calibrate the azimuth angle?

> Dear all,
>
>     I am Chiu-Teng Tsai (BM6ERA) from Taiwan. Now we are building a mobile
ground station. One of our problem is how to calibrate the azimuth angle.
Use compass only, or any better solution? Thanks for your help!
>
> Best regards,
>
> Chiu-Teng Tsai

Hi Chiu, BM6ERA

My reference source to calibrate the azimuth angle is the Sun at the
equinox.
I am fortunate enough because my horizon is free over the sea and I
know exactly the point near the island of Ischia in wich the sun set
belove the horizon during the spring equinox on march 21 and the
autumnal equinox on september 23

http://it.wikipedia.org/wiki/Equinozio

This reference point over the sea when the sun set during the equinox
is my geographical West or AZ=270 degrees

For several reason this point it is not accurate enought for precise
astronomical observation  but it is accurate enought to calibrate my
AZ=270° if the beamwidth of my  antenna at - 3 dB points is in the order
of 34 degrees like for my 13 dBdC 2M-22C for 2 meters or 25 degrees like
for my 15.2 dBdC  435-40CX for 70 cm.

By the way the above metod is not to be used for my 1.2 meters disc at
2400 MHz or any larger disc or yagi array for EME

In the case of 1.2 meter disc the gain is 27 dBi at 2400 MHz and the
beamwidth at - 3dB points is only 7 degrees but more important the feed
rarely is perfectly centered in the focal point so that the pencil of the
antenna can be affected by an unwanted  "squint" angle.

If I point a disc on the sun and I look at the shadow of the feed in the
center of the disc probably the pattern of the antenna is not perfectly
oriented towards the sun because of the "squint" affecting the feed.

For the above reason when the gain and directivity of the antenna are very
large I use InstantTrack to know with sufficient accuracy the Az and El
at the time of measuring the maximum level of sun-noise at the output
of my receiver and so now I can accurately calibrate my AZ and EL readout
accordingly.

Best 73" de

i8CVS Domenico






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