[amsat-bb] Re: Azimuth question
kl7uw at acsalaska.net
Sat Jan 9 19:02:16 PST 2010
At 04:11 PM 1/9/2010, Dave Guimont wrote:
> >A fraction of a degree per year, and at least once in the history of the
> >Earth the North and South magnetic poles reversed.
>Yes, I'm aware of that, it also rotates about 1° about true north,
>the earth wobbles a bit to change the AZ, but how
>many ham antennas in the world need that accuracy?
>And I doubt that the average ham can orient within more than 2° by eyeball!
> 73, Dave, WB6LLO
> dguimon1 at san.rr.com
> Disagree: I learn....
> Pulling for P3E...
>Sent via AMSAT-BB at amsat.org. Opinions expressed are those of the author.
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For 144 & 432 that is probably adequate. On 2400
the beamwidth of my 33-inch dish is 10.6 deg.
(24.9 dBi) so keeping a signal within 1dB,
probably requires 3 deg beamwidth and knowing
true north with an accuracy of 10% of that results in 0.3 deg accuracy.
Of course if you are doing something like eme on
1296 with a 16-foot dish the beamwidth is 3.38
deg. (34.9 dBi). For eme it is desirable to
track within 1db of maximum gain which may is
something like 1-deg. and 10% accuracy is 0.1
deg. How would you set up a dish azimuth so that
it is that accurate to true north? For eme it
usually requires comparison with tracking sw for
location of the Sun or Moon. At these freq. and
dish sizes one can detect solar and lunar noise
to peak onto, then adjust az and el calib. to match tracking sw az and el.
As it turns out my dish digital az-el readout has
0.1 deg. resolution so that is best I can
read. On the Yaesu B5400, one is lucky to
determine direction within 7.5 deg. for azimuth
and 3.75 deg. for elevation. Manually tracking
AO-40 with the B5400 was very touchy, as fine
adjustment is near impossible. But I did refine
my azimuth positioning using solar noise on 2400.
For 144 or 432 probably the most accurate method
for calib of azimuth is using a repeater many
miles away (knowing both its Lat-Lon and your
Lat-Lon with bearing sw that produces a great-circle bearing).
73, Ed - KL7UW, WD2XSH/45
BP40IQ 500 KHz - 10-GHz www.kl7uw.com
500-KHz/CW, 144-MHz EME, 1296-MHz EME
DUBUS Magazine USA Rep dubususa at hotmail.com
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