"Dave Liquorice" writes:

On Fri, 20 Sep 2013 03:56:08 GMT, Windmill wrote:

Does a dish motor automatically drive a dish back to the original
position if a gust moves it a fraction of a degree away?

It might if the system really knows, via some form of feedback where
the dish is but I don't think they do.

That's probably the case; I suspect (but don't know for sure - maybe
need to dig for the stuff about DisEqC I copied from a library book a
couple of years ago) that the receiver can tell the dish motor to go to
position 5, the dish motor can remember positions and the corresponding
azimuths when it's told to do so by the receiver (so the receiver can
later say 'Goto X' using the appropriate protocol), the dish motor can
have all positions reset (this one does it when you press both the 'Go
East' and 'Go West' manual buttons on the motor at the same time and
then power on (they can't have intended it to be easy!), but probably
the motor can't tell the receiver where it's pointed.

However it's still possible that even if the receiver doesn't know, the
dish motor might remember where it's pointed and move back there if a
gust blows it maybe 0.1 degrees away.

That would depend on the dish motor having some kind of shaft encoder
to tell it it's current position.

Otherwise, there would have to be a stepping motor pointing the dish
by just counting the number of steps. Which doesn't sound very good,
but maybe they do that.
(I'm just trying to guess semi-logically what the design might do).

Just align the dish to
satellites each end of the arc it can see and it just motors x amount
to find the ones in between. There could be some form of signal
strength feedback to "peak the alignment" when about in the right
place but that couldn't be used to keep the dish aligned as it
doesn't provide information about which way to move the dish.

Mmmm - couldn't you do that by moving one way a small amount until the
signal falls a little, then the other way until it rises then falls to
the same amount as before, and then split the difference?
But I doubt if there is such a feature, in this motor/receiver
combination at least.

The motor does have east and west limits which you set from the
receiver, but that doesn't prove that there is any position feedback to
the receiver from the motor.

Next time it happens move the dish to another sat and back again?

I've been reluctant to do that in case something goes wrong. Access to
the roof here is via a hatch in the upstairs neighbour's flat, so I
have to coordinate that with them, and if I can't get the dish pointed
correctly again I would lose satellite internet until I can go up.
(Also, I'm still not really clear about setting motor positions - the
booklet is translated from maybe the Chinese!)
Pointing to a TV satellite has to be fairly precise, but pointing to an
internet satellite has to be super-precise - a 3 watt transmitted
signal has to reach up 22,400 miles to the satellite.
Which is bloody well amazing, but it works.
Another case where Clarke's dictum is spot on: 'Any sufficiently
advanced technology is indistinguishable from magic'.
And very appropriate that it applies to satellites in the synchronous
orbits he suggested long ago.


--
Windmill, Use t m i l l
J.R.R. Tolkien:- @ S c o t s h o m e . c o m
All that is gold does not glister / Not all who wander are lost