August 2013 - AMSAT-BB - mailman.amsat.org

LO-19 on again
by Ib Christoffersen 12 Aug '13

12 Aug '13

hello all, This morning at 0828 UTC it was back on with the very strong signal. Dots and Dashes at random. Sorry if this is a double posting. Had some problems. 73 OZ1MY Ib

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Rotator Positioning questions
by Ing. Pavel Milanes Costa 12 Aug '13

12 Aug '13

Ok, I have now a paper design with the goal for my rotor project. This rotor is really a 0-360o, but I have managed (designed) to make it full stop on 0-450o (even 540o if I like... with two contact switches that cuts power to motor when in position) and will use a mixed reference setup, the same for elevation as 0o (horizon) to 90o (cenit) I can attach a plastic overlay to a wheel on the gear reduction for making a 90 shift signal (2 wires for AZ and 2 for EL) an then down in the controller a 74hc74 decoding the 90o to say/count not only the position, but also the real rotation direction, the reduction cuadrature signal outputs ~ 750 pulses for full 450o as per my calculations, this after decoding by 74hc74 will be ~375 pulses for 450o and about 1.2o of accuracy, and the controller knows if the system if de-phased by high winds as it gets extra pulses when no moving was requested... so it can correct this deviation... (this is not possible with "simple" pulse counting or "time" counting as Bob, WB4APR proposed) High winds here normal here, and as I say in a previous email the brake mechanism is working poorly, remember this is for a "small" camera mounted on top the device, not a "sail" of 2 crossed yaguis for 70 and 2 more for 2m The "motor running/motor stop" signal will be a current probe on the AC 24V motor feeding wires down the control, as when the motor reach 0o or 450o it automatically switch's off Now the real question is how to orient the rotor physically, I have ZERO rotor experience here... knowing it can do 0o-450o... 0o is north, and 450o is east, this is the way I see, so I can do E-W north (up) and south (down) ways as well as N-S in east (right) and west (left) ways This is correct? And from the point of view of the controller and PC, lets imagine a ~NNE to NW pass (80o to 300o pass, north way) The PC(software) knows that ZERO will be crossed and send the controller a 450-(real zimuth) to the controller? Or this job must be done IN the controller it self? With Azimuth and Elevation you can flip the direction of the pass an then flip elevation 180o and cover it 100%, but how to do this in azimuth only rotors? Another... in 450o rotors (no elevation) How you cover a 110 to 300 (~SEE to ~NNW) pass if 450o is East and 0o is Noth? Assuming the software can figure the ZERO crossing and can do the math, 110o is beyond the 450o (450 = 360+90)... How to manage this? If I make a 540o rotor: softwares can manage it? (1+1/2 turns against 1+1/4 turns of 450o?) I have the serial comms working on the pic (MCU) but this questions are hammering my head... Can anyone help me with this? 73 the CO7WT

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Update on my Noise problem on 75 Mtrs
by Dave Larsen PhD 12 Aug '13

12 Aug '13

2 Days ago abt 3am I was up and working 20 mtrs when our power went out .. I went outside and noticed some lights down from me , so went to main house breaker and it had triped - Tryed to reset it and would not .. long story short .. it was REAL BAD .. changed the 200 amp breaker out and Qrn is knw back to a S-3 .. here is a pic of it .. cut the breaker so I could see how bad it was http://imageshack.us/photo/my-images/850/om69.jpg/ TNX for everyone that sent back trying to help me in this matter .. Dave N6CO

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LO-19 changed to continuous carrier ?
by Ib Christoffersen 11 Aug '13

11 Aug '13

Hi, Here (Copenhagen, Denmark)at the AOS at 1213 UTC it sounds like just a single carrier with no modulation. LHCP seems to be best. It is not very strong like it has been for some time. Anybody else ? 73 OZ1MY Ib

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Cubesat 2013 Summer Workshop live video stream
by Samudra Haque 10 Aug '13

10 Aug '13

FYI, I'm at Cubesat workshop @USU.. Link for live video stream is provided below. http://www.ustream.tv/channel/cubesat-summer-workshop-2013?utm_campaign=www… Samudra Haque, Ph.D Student Dept of Mechanical and Aerospace Engineering George Washington University

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Non-mechanical feedback follow up
by Zach Leffke 10 Aug '13

10 Aug '13

Hello again everyone, I have received a couple of emails off list asking about details of how I'm planning to use the magnetometer for the azimuth feedback. Instead of individually replying I'm placing my response here so everyone gets the same info (skip to the end of this long winded email for the details). Before I get into that I want to address Bob's (WB4APR) note about the constant rate of these motors. Basically, I like the idea because of its simplicity. That's something I hadn't considered, but will look into. My logic there is run my system through a few dozen trials to really lock down the turn rate baseline. Then all I have to do is keep track of the amount of time and in which direction I'm telling the motors to turn, and voila I should know the azimuth/elevation. As Bob mentioned with the beamwidth of these antennas that should get me close enough. If I were only planning to use the system for tracking LEO birds at VHF/UHF frequencies, I would probably just go with that. However, I was slightly understating my goals when I initially brought up this issue. In addition to LEO birds, I plan to also use this system for UAV tracking and High Altitude Balloon Tracking. I am an EE graduate student at Virginia Tech and each semester I help out with an Undergraduate Lab with Aerospace and EE students that design and fly a high altitude balloon (generally with APRS tracking and some kind of camera/sensor suite payload). One of the professor in charge's (Dr. Dennis Sweeney, WA4LPR, some folks might know him for his filter design work among many other things) goals is to up the data rate in order to attempt a high speed real time data link. So in my own time I want to use this tracking pedestal for LEO tracking (and for my Master's Thesis prototype), but for this HAB project, the elevation can get quite high depending on the geometry of our chase scenario, and beamwidths can get quite small depending on the frequency we finally choose. In the end it might not matter much, but when we get to that point I want to at least have the OPTION for tight control over the pointing. This whole thing will likely get vehicle mounted in the bed of my pickup, and though I haven't completely thought out the details yet, My gut is telling me the use of a magnetometer for azimuth feedback could have a slight advantage because as the vehicle is moving the system could automatically compensate for the turning of the vehicle, where as a potentiometer type solution would not. With position updates from the HAB and a local GPS in the chase vehicle, calculation of Az/El to the target is pretty straight forward. Combine that with magnetometer feedback about the antennas' azimuth and elevation feedback from an accelerometer (which should also be somewhat "self compensating", say if the vehicle were moving up or down a hill), and I should be able to come up with a fairly sexy tracking pedestal that automatically compensates for the vehicle's motion to keep the antennas "on target." All that being said, here is my plan for the magnetometer implementation: I don't really have the details locked down yet, but I can give the overall plans. First I plan to use the HMC5883L from sparkfun. This device is $14.95 + Shipping and handling. It is a 3 axis magnetometer. When dealing with magnetometers it is important to understand whether or not your device is tilt compensated. This particular device is NOT tilt compensated. What that means is that it must be kept oriented parallel with the Earth (within say maybe + or - ten degrees or so). Assuming it remains oriented properly, the device will output (over I2C) the magnetic field strength in the X, Y, and Z directions. The Z direction is essentially pointed straight up at zenith (and should remain near zero since it is orthogonal to the earth's magnetic field). Also assuming no other strong magnetic fields exist near the sensor, it will detect Earth's magnetic field (the sensor just returns the highest magnetic field for a particular direction, so if other magnetic fields exist near the sensor, it can ruin the readings). In order to get the bearing, or azimuth, information one simply has to use the atan2 function with the Y and X axes, here is the code snippet from some examples online: heading = atan2(scaled.YAxis, scaled.XAxis). The rest is just calibration and making sure the heading makes sense (i.e. if the heading is a negative number add 360 to get a 0 - 360 output). One issue too is that most satellite tracking programs return the TRUE heading or azimuth (reference to the North Pole) to the spacecraft. This magnetometer with produce a MAGNETIC azimuth (referenced to the magnetic pole). Thus one must compensate for the magnetic declination of the area of operation. The declination can be found online for each person's individual location and can be hard coded into the code to adjust the magnetic readout to a true readout. Since this device is not tilt compensated I plan to mount it on my azimuth base on a short boom that sticks straight out in front of the antenna assembly. It will be center mounted on a non-conductive extension (maybe two or three feet in front of the azimuth assembly). My logic here is to try to get the sensor as far away from the AC induction motors and other metals as I can. The AC motors will produce a strong magnetic field and if the sensor is near them, it will distort the readings. Thanks again to everyone that provided feedback for me. Below are a few links that should help out those who want more details. Keep in mind too that there is a plethora of information out there on these devices (tutorials and example code) and with the links below and some skillful Googling, anyone can found out everything they need to make one of these work. Sparkfun Link: https://www.sparkfun.com/products/10530 Bildr Tutorial: http://bildr.org/2012/02/hmc5883l_arduino/ K3NG's Arduino rotator control project: http://blog.radioartisan.com/yaesu-rotator-computer-serial-interface/ (Thanks to Lizeth, N3YKF for pointing me in this direction) --------------- -Zach, KJ4QLP

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AMSAT Awards
by Bruce 10 Aug '13

10 Aug '13

As the AMSAT server is being rebuilt, I have just rebuilt all the AMSAT award pages. You can reach them by going to amsat.org and clicking on Services. You will find Awards under the drop down. At the bottom of the main page is a link to all the award recipients. This information will be the same information that appears on my website. I will keep them both up to date. 73...bruce -- Bruce Paige, KK5DO AMSAT Director Contests and Awards ARRL Awards Manager (WAS, 5BWAS, VUCC), VE Houston AMSAT Net - Wed 0100z on Echolink - Conference *AMSAT* Also live streaming MP3 at http://www.amsatnet.com Podcast at http://www.amsatnet.com/podcast.xml or iTunes Latest satellite news on the ARRL Audio News http://www.arrl.org AMSAT on Twitter http://www.twitter.com/amsat

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Astronaut Mike Foale KB5UAC Leaves NASA
by Clint Bradford 09 Aug '13

09 Aug '13

Astronaut Michael Foale Leaves NASA After 26-year Career NASA astronaut Michael Foale has retired, ending a 26-year space agency career that included 375 days in space during six space shuttle missions and extended stays aboard two space stations. Foale spent 145 days aboard the Russian space station Mir in 1997 and 194 days aboard the International Space Station as commander of Expedition 8 from October 2003 to April 2004. He also conducted four spacewalks over his NASA career totaling almost 23 hours. "We salute Mike and his contributions to NASA as an accomplished member of the astronaut corps," said NASA Administrator Charles Bolden. "Starting with his first flight, shuttle mission STS-45, when we flew together in 1992, Mike has worked tirelessly to support NASA's quest to explore the unknown. I know Mike will go on to do more great things as he continues to support the aerospace industry in his new endeavor." Foale held many positions during his NASA career, including chief of the Astronaut Office Expedition Corps, assistant director (technical) of the agency's Johnson Space Center in Houston, and deputy associate administrator for exploration operations at NASA Headquarters in Washington. He most recently worked in support of Soyuz and International Space Station operations, as well as space station spacewalk activity and spacesuit development. Foale's future plans include advancing green aviation technology. For Foale's complete NASA biography, visit: http://go.nasa.gov/14gPLKx For more information about NASA programs, visit: http://www.nasa.gov -end-

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ArduSats and ITAR
by M5AKA 09 Aug '13

09 Aug '13

One of the designers of the ArduSat-1 and ArduSat-X CubeSats, Australian Jonathan Oxer who passed his amateur radio Foundation exam last February, was interviewed for an article that has been published in The Register. In the interview he mentions that ITAR has currently stopped the design of the payload being released under the TAPR Open Hardware License. See http://amsat-uk.org/2013/08/09/ardusat-open-source-ham-radio-cubesats/ ---- 73 Trevor M5AKA AMSAT-UK website http://amsat-uk.org/ Facebook https://www.facebook.com/pages/AMSAT-UK/208113275898396 Twitter https://twitter.com/AMSAT_UK ----

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Re: magnetic reed switches f(not really needed)
by Robert Bruninga 09 Aug '13

09 Aug '13

These motors run at a nearly constant rate. ALl you have to do to know position is to keep track of the time they are on. It remains calibated because at the end of every pass (it ends at zero elevation) so you konw you are at 0 (include say a 10% overshoot after the pass to be sure it is at 0). Same for Azimuth. Each time you find yourself within 45 degrees of the mechanical stop at south (or north), after the pass, send the rotator to the stop with again, 10% overshoot, this re-establishes that reference. So, no feedback needed (for the beamwidths of VHF and UHF anyway). Oh, and you dont need elevation at all really for all LEO satellites. See http://aprs.org/rotator1.html Bob, WB4APR On Fri, Aug 9, 2013 at 6:00 AM, Robert C. Campbell <kb3pmr(a)gmail.com> wrote: > I am using reed switches for both my AZ and EL visual feed back on my > newest build. I have had to slow the motors down with a PWM so that the > reeds don't skip a count. Both AZ and EL are still within the speed of > keeping up with ISS. You can determine the ratio of motor turns to one > revolution of the AZ full 360 or 90/180 for the EL and use that ratio to > determine the position in degrees. Repeat-ability seems very good. If you > are going visual/manual positioning you can check on utube or > instructables.com and find a easy build for a modified $ 2.00 Dollar > General calculator that then becomes a pulse counter by simply connecting > the enter button to your reed and entering the ratio and pressing the plus > sign. Then each rotation the calculator will tell you the degrees the > antenna is looking at. Yes, it does need reset after each pass, and yes, if > you run by the bird and go back the calculator will give you some extra > counts since it is counting reed switch contacts not true degrees of > indication. Purchase 5 of them, one for practice, 2 for EL and 2 for AL > then if you start from the same standard position each time one can add and > one can subtract. This should work fine assuming that the driver maintains > mental focus. It is a small fun project and cheaper then happy hour at the > local pub. The Pulse Width Modulator works good with this because you can > adjust the speed of the motors to keep up with the bird. This of course > assumes you are working with direct current motors. > > Bob > _______________________________________________ > Sent via AMSAT-BB(a)amsat.org. Opinions expressed are those of the author. > Not an AMSAT-NA member? Join now to support the amateur satellite program! > Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb

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