[amsat-bb] New Rotator X/Y as opposed to Azimuth/Elevation SPX X-Y Rotor

[Robert Bruninga]

Unless you live at low latitudes, an X/Y system has twice the problem as
the AZ/EL does directly overhead, because it has moved the "axis" problem
to the horizon directly North and South.  So if you are at reasonably high
latitude and trying to track the ISS across your south, you have the same
problem.  It takes the X/Y a LONG time to go from 179 degrees to 181
degrees azimuth since the Y motor has to go a full 180 degrees to get
across the X axis (south)..  If the system operates at 1 RPM, that can
take a full 30 seconds.

The X/Y is best for tracking things that do most of their work "overhead"
but  are bad for things that swing through south with a low horizon
(assuming you are in the northern hemisphere.).  And since all LEO
spacecraft spend 98% of their entire pass times well below 70 degrees and
so they are definitely -not- "overhead" type space applications.

For example, the ISS has maybe one "overhead" pass above say 70 degreees
only once every few days, which might have a few second problem in
tracking, but the signal is so strong as to be inconsequential.  Whereas
the ISS will go through at least 2 or 3 pasess every day through south
where the X/Y will have the same significant delay, BUT the delay is
ocuring when the spacecraft is down on the horizon where you need the gain
the most because it is 10 dB farther away.

See the real-world geometry of a LEO orbit and it is quickly obvious why
there is very little "overhead" operations in the Amateur Satellite
Service with LEO spacecraft.  http://aprs.org/LEO-tracking.html

The thing about leo satelites (and the ISS) is that when it is directly
overhead (a problem for the AZ/EL) it is 10 dB closer and very strong and
needs no gain at all.  And the duration of any pass above 70 degrees lasts
only a few seconds.

We have a 12 meter X/Y and we are at 39 deg North Latitude and cannot
track the ISS on any low  southern crossing.  We have to choose one side
or the other and lose the other side.  But this was back in 199? when we
were one of three successful uplink stations to the Shuttle on STS-37 with
Amateur TV color Video.



-----Original Message-----
From: amsat-bb-bounces at amsat.org [mailto:amsat-bb-bounces at amsat.org] On
Behalf Of Daniel Cussen
Sent: Monday, October 13, 2014 6:15 AM
To: AMSAT
Subject: [amsat-bb] New Rotator X/Y as opposed to Azimuth/Elevation SPX
X-Y Rotor

New Rotator X/Y as opposed to Azimuth/Elevation SPX X-Y Rotor

I am thinking of purchasing a new tracking system design, which uses an
unusual way of pointing the antenna. I was wondering if anyone else has
used this product or even the nearly identical non XY model?

http://www.rfhamdesign.com/products/spx-light-antenna-rotator/spx-x-y-roto
r/index.php#

Youtube video at the bottom does not work.

The benefits of it are supposedly better/faster positioning at the
elevation peak, due to the "two elevation, one over another" design.

There is a good description of why it might be good here:
Scroll down to conclusions
http://www.microwavejournal.com/articles/2937-selecting-a-pedestal-for-tra
cking-leo-satellites-at-ka-band

There are other benefits:
630 Euro plus shipping including USB computer interface (cheaper than
Yaesu) Fast motor movement (50 seconds for 360 degrees) Can be compatable
with Yaesu GS232 protocol or SPID driver

Downsides
Low strength 80nM only suitable for light antennas (such as the arrow etc)
Brand new model may have bugs or weaknesses
1 degree max position accurancy sensed by reed switch. Not 0.1 degrees as
per some expensive systems.
Cheaper computer interface/features compared to more expensive models.
Not available from anywhere else (yet)
3 weeks minimum delivery time
Strange to understand design
Strange to understand config. The az & el degrees are converted to XY
positions.

The main reason for taking the risk, is I want to do some small dish tests
for HAMTV from the ISS, and even most expensive tracking systems, are too
slow at fast peak elevations, particularly with narrow beamwidth dishes.

So has anyone used one of these or any thoughts/comments on the design?

Dan EI9FHB
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