[amsat-bb] To Flip or Not to Flip

Daniel Cussen dan at post.com
Fri Jun 27 15:27:53 UTC 2014

To  Flip or Not to Flip

Ok, my setup has flip capability. It also has azimuth of 1.5 turns
(540 degrees),
So flip is not essential for end stops as the rotator neither stops at
North nor South

The rotator controller software only works in WiSPDDE but this can use
many different tracking software types.
Currently using Orbitron. Orbitron only outputs Elevation 0-90 and Az 0-360

The WiSPDDE rotator driver has been modified to automatically flip if
elevation goes above 70 degrees and starts to drop again. As soon as
it starts to drop Elevation, Azimuth value has 180 degrees added and
Elevation is now suddenly >90

The software has the option to enable or disable flip on each pass.

What I need to know is

1) What is the best way to predict if I should flip or instead just
move the azimuth without flipping?

2) Is there any software to automatically decide if Flip is best, and
output Elevation values >180 to WiSPDDE during the middle of a pass?

For Example worst case would be a satellite coming from due west (270)
heading east (90).
I this case it would be best to flip antenna, otherwise azimuth would
need to rotate 180 degrees suddenly during a pass.

In another case, ISS coming from south west across to south and then
south east, but with elevation approaching 85 degrees. In this case it
would be best to not flip, but our current software flips once the box
is ticked and if the elevation rises above 70 degrees.

At the moment it is not possible to do this in WiSPDDE as it does not
know where the ISS is going to be at the end of the pass as that info
is not sent over the DDE interface.

Specific System Setup
The system will be used to track the ISS for 2.4Ghz HAMTV downlink.
The beamwidth of dish is 4 to 8 degrees, but signal is very strong at
high elevations.
Video is used live so continous accurate tracking is needed
The azimuth can be any value 0-540 degrees (1.5 turns). Currently the
software can do 2 things.

1) Not flip but instead move to an azimuth position where flip is not
essential, but sometimes the azimuth is too slow to get to the new

2) Flip the dish, but on some passes it would be better to not flip
the dish, if say elevation went to 73 elevation but azimuth could cope
with tracking.
The decision is currently a tick box. Orbitron only outputs 0-90
Elevation so WiSPDDE is not being told by Orbitron to flip, the
decision is not based on the pass prediction.

I believe some of these problems may be solved with SatPC32 but we
would possibly need to modify our custom driver to just accept these
If using SatPC32 would it solve all these issues? Can it decide to
flip or not flip based on azimuth speed and pass prediction in the
middle of a pass?
Does SatPC32 only ever flip at the start of a pass and never in the
middle of a pass?
Will it pick the best option for every pass and output values via DDE

The rotator WiSPDDE is specifically written for this task,
It is a modified version specially modified by Amasat Itallia.
The rotator we are using is prosistel Azimuth and Elevation rotator.
This is quite new and so a specific driver was written.
The azimuth can achieve 1.5 turns (540 degrees) and Elevation 180. The
manufacturer only specifies Az 360 and Elev 90 but we have special
modified hardware and software to allow movement above normal range.
We have been using Orbitron up to now as it allows sun tracking which
is handy for dish calibration,

In reality the setup may not be used too often for school contacts and
we could perform a manual pre-test or simulation to see if flip is
Another option is to just not use passes for school contacts that
require flip or that will result in a signal loss in the middle of a

What I would like to happen is the software to calculate which option
is best, to flip on the fly or not to flip
The decision would be based on the speed of the motors and which mode
is fastest to keep a signal locked.

For example

Time in seconds 1 	AZ 260 El 45
Time in seconds 2	Az 90 El 80

Assuming both Elevation and Azimuth can move a 5 degrees per second
Difference without Flip
Az 170	El 35 Max Time to correct position 34 seconds
Difference with Flip
AZ 10	El 50 Max time to correct position 10 seconds

So is there any program that does this and can output to WiSPDDE?


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