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Posted by John Wilson on 10/11/05 01:14
Polar mounted reflectors will accurately track the Clark belt if
installed and aligned correctly for the east/west limits. They are a
compromise in the sense that the earth is located physically too close
to the geostationary arc for the reflector (antenna) to "see" the target
satellite with an adjustment to the declination or "squint" angle the
value of which is based upon the viewer's
latitude. The reflector (antenna) typically is raised slightly up on
the polar mount to more accurately boresight the target reception
satellite.
Ku band reflectors (antennas) were never designed to be mounted on a
steerable polar mount.
They were designed to be stationairy pointed on a target satellite using
an lnbf feed. However,
in Europe DBS implementation was via Ku band equipment and C band not
used for DBS applications for a number of reasons both technical and
political. Many ku band signals crossed country borders. There was
interest in receiving multiple ku band satellites. So somebody mounted
a ku band reflector on a motor and it works with limited success.
However,
these ku antenna mounts do not have the declination offset adjustment
capability. Therefore there will be a tracking error of varying degree
depending upon the installation. The error will not be noticeable on
strong downlinked signals but it may on weaker signals. This European
ku band satellite reception process has been implented in the US with
varying degrees of success.
HTH are polar mounts allowing an actuator "throw" of hopefully close
to 180 degrees. Again is the antenna is not aligned correctly it will
not track the arc accurately.
That briefly is the reason for the declination offset adjustment and
the historical reasons why large reflectors (antennas) had it and small
ku band reflectors (antenna) didn't and still don't.
rose wrote:
> Do polar mounts accurately track the Clark belt satellites
> or are they just a compromise, compared to HH mounted dishes?
>
> Or are polar mounts just for BUDs and not for Ku size dishes.
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