Re: [amsat-bb] Tracking AO-40 w/ C band - observations

["Bill Jones" <wejones@xxxxxxxxxxxx>]

> >* Without the benefit of a horizon-horizon mount,  my dish will
> >only provide azimuth coverage from 180 to 250 degrees.  This
> >limits reception possibilities quite a bit.
> 
> ## I find your limited dish movement angle surprizing.  I have installed
> over 100 professionally and can usually get about 120 degrees of movement
> before the actuator arm limits. 

I'm not sure if you are referring to actual degrees on the mount, or 
degrees of longitude of satellite position, but I don't think I agree 
completely with this if  the latter.  Actuator arm limit is usually not 
the problem, but rather that the back of the dish jams against the 
actuator arm, so that no matter how long the arm is, it won't push 
the dish any further.  When I used to use an actuator (I now have a 
H-H) , I could reach from my westerly horizon (sats at about 
137deg longitude) to somewhere around 55 deg longitude, at which 
point I still had a good deal of throw on the actuator, but the 
actuator jammed into the back of the dish.  There is a work-around 
to this, which involves  welding on an extension to the point where 
the actuator attaches to the dish.  This holds the actuator off away 
from the dish a bit more allowing it to move further.  However, 
without welding on this extension, I think you'd be limited to a lot 
less than 120 degrees of  longitude.  I think the actual angle of 
movement on the dish mount would be more than the number of 
degrees of longitude covered, however, so I suspect that you might 
be really saying the same thing as the previous poster.
 
> >* The declination offset of three different dishes (two 10', one 8')
> >only allows for declination adjustment plus-minus 5 degrees,  again
> >limiting possibilities if the feed is at the prime focus.  Offsetting the
> >S band feed would help somewhat,  but I guess this would introduce
> >a risk of illumination spill-over.
> 
> ## Declination for our latitude ~61 degrees North is 8.6 degrees.  Most
> dishes are capable of about 9.5 degrees.  Offset is only down ward as there
> is no need for an upward offset.  In the southern hemisphere the dish faces
> north so the offset is still downward.

I agree that you would only ever use a declination down, but some 
dish mounts do have an up and down adjustment, in particular the 
Orbitron dishes that have "spinclination" allow for up to + / - 8 
degrees.  This doesn't change your argument though, as you'd 
never use the up adjustment.

> Changing the declination offset would only be an option if the dish were
> dedicated to ham use only.  It should not be changed if still used for TV.

One option that I don't think anyone mentioned (sorry if it has), is 
that you can purchase a declination motor, which is basically just 
a second actuator connected in place of the "inclination" screw (I 
think), so it wasn't truely declination, but accomplished the same 
thing.  If controlled by a separate controller, this can give you quite 
a bit of range above and below the Clarke belt, and you can return 
it to the belt for TVRO when you are done.  These declination 
motors are usually used for inclined satellites such as SBS4, etc.

 
 *****************************************************************
 *Bill Jones  N3JLQ  Sweden Maine                                *
 * wejones@megalink.net                                          *
 * Main home page   http://www.megalink.net/~wejones             *
 * WWII/B-17 page   http://www.megalink.net/~wejones/wwii.html   *
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