[HCARC] Robotics/ Satellite Tracking Rotator

Sat Aug 19 18:10:51 EDT 2017

Gale,

I'm not quite sure what your application is.  If it is tracking 
satellites at 2 m and 70 cm your tracking requirements aren't very 
difficult.  In the early days of Oscar I used a 10m 3-element Yagi and a 
3-element 2 m Yagi.  The 10 m antenna was not up very high and so had 
little directivity and most of the pattern was up.  The 2 m yagi also 
had a 3 dB beamwidth of about 60 degrees.  The 2 m antenna was mounted 
at an angle of 45 degrees above the horizon. I would only have to move 
the antenna twice to cover the longest pass.  60 degrees is 
approximately a radian.

When you look at an optical telescope, because the wavelength is so 
short, the beamwidth is very much narrower, even for small telescopes.  
A 4 inch (10 cm) aperture telescope would have a beamwidth on the order 
of a microradian, a million times narrower than 3-element Yagis.

To track the early OSCAR satellites in polar orbit all you really needed 
was the time and location of the equator crossings which was transmitted 
by W1AW.  Life is infinitely easier now.  I use a program called 
Gpredict.  It has as an output polar and az-el plots of the satellite 
you specify at your location and includes time data.  It uses the two 
line element sets (TLEs) from US Space Command.

Even a 1 m dish at X-band has a beamwidth of about a tenth of a radian, 
6 degrees.

If you recall when direct satellite TV at Ku band first started, you 
were able to aim the dish close enough to the correct location knowing 
only your lat and lon and a magnetic compass and the built in elevation 
scale on the dish mount.  With your lat and lon, the satellite receiver 
gave you the compass bearing and elevation setting to aim the dish.

If you haven't already, you need to take a look at the satellite 
tracking programs available like Gpredict to see the type tracking data 
available and use it to look at the amount of change of azimuth and 
elevation and the time during a pass.  That should help you decide how 
much resolution and speed you need to do the tracking.  I think you will 
be surprised how low the resolution and speed requirements really are.

I would recommend reading "The Satellite Experimenters Handbook" 1st 
edition (1985) by the ARRL.  It really gives a practical feel for how to 
do it and the equipment required.  Like so many things in ham radio, the 
manufacturers and the ARRL have gone out of their way, in the interest 
of profits, making simple things incredibly complicated.

Kerry

On 8/19/2017 3:25 PM, Gale Heise wrote:
> A number of people responded so I’m going to simply reply to the reflector and please just ignore me if you’re not interested.
>
> First I’d like to thank John Trolinger for providing input previously.  He has a neat satellite tracking system at his place by simply pointing the antennas at 45 degrees and utilizes a Channel Master rotator.  He connects his computer to the rotator via a computer interface and can track the satellites.  I’m trying to see if there is a simple and inexpensive way to obtain elevation control as well as azimuth.
>
> Also, thanks to those expressing an interest in helping me and learning more about robotics.
>
> Today many hams are working satellite stations simply with hand held antennas such as the Arrow 146/437-10WBP.
> http://www.arrowantennas.com/arrowii/146-437.html
>
> Here is an example of someone working a satellite with a tripod:
> https://www.youtube.com/watch?v=1HfvmU_utI8
>
> Attempting to locating the satellite and track it manually is very frustrating as I have found the case through personal experience.  To purchase a Yaesu G-5500 AZ/EL rotator, cable and computer interface box it is expensive ($1,000+) and overkill for a hand held or small array antenna system.
>
> As a result, I started searching the internet for a less expensive alternative with the WRAPS system as one choice.  The first video is by the inventor and the subsequent videos are by a person who actually built the WRAPS system from parts:
> https://www.youtube.com/watch?v=K5Xx6K7tM0Y
>
> Wraps Assembly and Testing – Unless you understand Spanish, skip Video #2
> 1. https://www.youtube.com/watch?v=gntz0d-NQPc
> 2. https://www.youtube.com/watch?v=Nze3ZFRupuM
> 3. https://www.youtube.com/watch?v=XqTkkQYNYd0
> 4. https://www.youtube.com/watch?v=2tFw8tz7WW0
> 5. https://www.youtube.com/watch?v=qJOKr1KcVoY
>
> I thought the WRAPS system was on the lightly constructed side and not really meant to be all weather.  It addition, it’s about $300 for the parts.  So I began looking for existing systems that could be adapted.  One idea came to me when I thought about my neighbor who has a tracking system on his telescope and I found this video:
> https://www.youtube.com/watch?v=BDTjnJm41mc
>
> Here is a link to purchasing a telescope mount:
> https://www.celestron.com/products/nexstar-slt-computerized-mount
>
> It also requires a computer interface:
> https://www.amazon.com/s/ref=nb_sb_ss_c_1_10?url=search-alias%3Daps&field-keywords=skyfi+wireless+telescope+controller&sprefix=skyfi+wire%2Caps%2C295&crid=2RZ1O8B4040C6&rh=i%3Aaps%2Ck%3Askyfi+wireless+telescope+controller
>
> Again, the price is way more that I want to invest.  Over half of the cost of the G-5500.  So I continued to search for an all weather system and came across a video that I can’t find now.  It was of a fellow utilizing a Defender Security pan/ tilt camera platform.  He utilized the matching controller and manually tracked the satellite.  Here is a heavier duty model built for the weather:
> https://www.amazon.com/Defender-Security-82-12440-Outdoor-Heavy/dp/B002MZ8GU2/ref=sr_1_sc_1?s=electronics&ie=UTF8&qid=1503171732&sr=1-1-spell&keywords=defendersecurity+pan+tilt
>
> There’s a Techno-Geek website called hackaday.io.  On it’s site I found a fellow who purchased the Defender Security 882-12440 and built a controller for it to swing up and down, back and forth to water his lawn.  He has five different files posted showing his progress through the project beginning with a disassembly of the unit to take a look inside:
> https://hackaday.io/project/20572-ptsprinkler/log/57784-dissecting-the-pantilt-stage
>
> In addition, here is a video from AE0MT who is utilizing an inclinometer and GPS chip;
> https://www.youtube.com/watch?v=HE09wMaTUpU
>
> There was another satellite video whereas the fellow was utilizing a stepping motor to obtain feedback on position rather than a potentiometer system as utilized in the WRAPS system.
>
> Here’s where I’m looking for input.  One can purchase the Defender Outdoor Heavy Duty Pan Tilt for about $60.  I believe the fellow who assembled the WRAPS system said the electronics parts were about half the total cost so about $150.  So I’m curious if there is any way to add positioning feedback to the Defender and control it with a computer as with the WRAPS system.  It may mean replacing the motors within the Defender with stepping motors in order to obtain feedback for the positioning system or adding inclinometer and GPS chips as did AE0MT.
>
> It’s a lot to wade through so I’m not offended if people aren’t interested in pursuing.  If you get through it all I’d appreciate your thoughts.
>
> Take care,
>
> Gale
> KM4DR
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