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

magnetic reed switches for indication
by Robert C. Campbell 09 Aug '13

09 Aug '13

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

1 0

Non-mechanical Azimuth/Elevation Feedback Advice
by Zach Leffke 09 Aug '13

09 Aug '13

Hello Everyone, I recently came into possession of a Pelco PT170-24P tracking pan tilt pedestal designed to support large security cameras. My intent with this new acquisition is to repurpose it as a "low cost" (got it on Ebay for ~$75 + S&H) alternative for an antenna tracking pedestal for amateur satellites. It uses 24VAC induction motors to move the azimuth and elevation assemblies, pretty much just like the G5500s that I'm sure so many of us are familiar with. It definitely cannot support the same amount of weight as the G5500, but I'm looking to construct a small, portable satellite ground station node and this thing is plenty beefy enough to handle a couple of Arrow style antennas. Here is the problem, it provides absolutely no feedback. My question to the group is does anyone know of a non-mechanical method for getting relatively accurate feedback for azimuth and elevation. I'm looking for an all electronic means that I can mount somewhere outside of the actual pedestal assembly (like perhaps on the cross-boom) that will be able to provide measurement of the az/el (or pan/tilt, or yaw/pitch, whatever you want to call it) position. I'm using an arduino microcontroller for the tracking controller. Originally I intended to find a way to mount potentiometers in inside the unit and simply use the ADCs on the arduino to read the position feedback voltage from the pots, however, there is barely enough space to mount an elevation feedback pot inside the unit, and there is virtually no space for an azimuth feedback pot. Hence I'm looking for a non-mechanical method. My first thoughts for the elevation feedback was to use the old potentiometer plus nice heavy weight method mounted out on the boom. This idea doesn't appeal to me very much as other factors can now affect the position feedback (such as high winds). I then thought of something along the lines of an accelerometer. I also tossed around the idea of a 2-axis gyro for both Az/El. My issue is I have limited experience working with these types of sensors, and was hoping to get advice from everyone in this group. I know for example that the gyro will provide rate of motion around an axis and thus I have to integrate over time to get the actual position. This becomes cumbersome because now I have to keep track of time in the Arduino while executing movement commands (certainly do-able, just more complicated than reading an ADC voltage). Additionally, I believe these devices suffer from drift and require frequent calibration (although there may be a scheme of starting from a known position, say at one of the limit switch contact points, for each pass that might work). I also toyed with the idea of an electric compass for azimuth feedback, but I'm worried about distortion of the magnetic field near the pedestal due to the AC induction motors or when the antennas are radiating. In theory the motors are housed inside the metal pedestal enclosure and thus are shielded from the outside world, but I can just see it now, nice steady feedback when the pedestal is stopped and as soon as I execute a motion command the azimuth feedback starts dancing all over the place. Since the motion stop command is based on achieving the target position, system instability is sure to occur. Even if I solve the AC motor EMI problem, I still worry that when transmitting the fields could potentially be distorted if near the antenna (remember my goal is a compact design) and taint the position feedback. Any ideas from the group would be greatly appreciated. I'm looking for a "sparkfun" type solution here and if anyone has experience working with accelerometers, gyros, electric compasses, etc. I would love your advice on which might be the way to go for the position feedback. If you think I've hit on a good idea above and should go with it please let me know. Again I'm using an Arduino, so analog voltage feedback, I2C, SPI, and UART serial are all on the table for communicating with the sensors to get the feedback info. Thanks in advance! Sincerely, Zach, KJ4QLP

6 7

Re: Satellites List
by Clint Bradford 09 Aug '13

09 Aug '13

>> ... I have summarized in my web site for the latest Satellites information ... And as I have publicly stated here and privately written to you, I am in awe of the historical value of this document. I started working on a "Top 250 Questions Asked of ISS Astronauts" - Q&A from the ARISS contacts ... thinking that that would be valuable for students (of all ages) as a reference work ... Clint K6LCS

1 0

Re: V/U Linear Transponder
by Tanan Rangseeprom HS1JAN 09 Aug '13

09 Aug '13

Dear David G0MRF Thanks you very much for file present of FUNCUBE satellites. I 'm sorry for reply to you late. I have work out of country. on august 4, 2013 have RAST meeting. I have present for JAISAT-1 project. please you seen at web site http://www.qsl.net/rast/ I would like answer the question.of you as follows. 1.Thailand has regular to forbid for transmitt UHF band but can receive the signal for amateur radio satellites only. we need to used VHF band same like transponder FO-29 AO-51 SO-50 and other satellites. for interference from China Thailand and other countries on VHF is normal. 2.Ok, please advice me for circuit diagram of V/U liner transponder. 3.We have to basic design FM repeater use to modify HX1 / RX2A RADIOMETRIX VHF / UHF transmitter module we have change x-tal to 145.90 MHz used x-tal 13.59 MHz and used MC3361 with x-tal IF 10.245 MHz and CML IC FX465 CTCSS Encode/Decode build test it to be via balloon successful. On this time we and technical team of TAMSAT group need help very urgent. we need advice of circuit diagram or datasheet IC for build V/U Liner transponder for payload 1U cubesat of JAISAT-1 satellite project. best regards Tanan Rangseeprom HS1JAN Project Manager of JAISAT-1 member of RAST ----- Original Message ----- From: <g0mrf(a)aol.com> To: <hs1jan(a)tamsat.org> Sent: Monday, July 29, 2013 5:24 PM Subject: Re: [amsat-bb] V/U Linear Transponder Dear Tanan. Thanks for the mail via AMSAT.org My name is David Bowman G0MRF and I'm a member of the team building FUNcube, due for launch this November. I can help with transponder design, but there are some points which you need to consider. 1) The use of V band for the uplink will be a poor choice for your location. The interference from China and other countries on 145MHz will mean the transponder will not be usable. Using U band for the uplink is a much better choice. 2) The 100kHz bandwidth is too much for the typical power available from a CubeSat. If you get your RF team to do a link budget analysis, you will see the cubesat power budget will not support 100kHz of bandwidth. Ususally 30kHz is as much as you can do with a 1U cube. 3) You may want to consider a FM 'repeater' as there is now only 1 in orbit, while there are several linear transponder satellites ready to be launched. The FM design will allow you to run a very efficient power amplifier (70%) and power can be saved over oceans and areas of low population by using a 67Hz access tone (CML FX465) I can assist with design but would need to know if you are planning a 1U 2U or 3U design. William PE???? is good, but will probably just offer to sell you a transponder. Regards David G0MRF some old info is available at www.g0mrf.com/transponder.htm The attached powerpoint has some pictures of the UV transponder and other boards in FUNcube from AMSAT-UK -----Original Message----- From: Tanan Rangseeprom HS1JAN <hs1jan(a)tamsat.org> To: amsat-bb <amsat-bb(a)amsat.org> Sent: Sun, 28 Jul 2013 17:48 Subject: [amsat-bb] V/U Linear Transponder Dear Sir; My name Mr.Tanan Rangseeprom my callsign HS1JAN. I need help and advice from you for circuit diagram of V/U Liner transponder .I and team want to build it for payload of JAISAT-1 amateur radio satellites of Thailand. JAISAT means is HEART in thai language. JAISAT is Joint Academies Intelligent Satellites for Amateur Radio of Thailand. this is project research and developmentean consists of RAST and Amateur Radio University inThailand both instructor and students. JAISAT-1 have payload liner transponder V/U uplink at 145.800 - 145.90 MHz and Downlink at 435.10 - 435.20 MHz on CW/SSB to fit in CUBESAT design. but this time I and technical team have no knowledge of the circuit diagram of liner transponder V/U. So you can help and advice me for Electronic Circuit Diagram of liner transponder V/U. Best Regards Tanan Rangseeprom HS1JAN / XU7ADN Project Manager of JAISAT-1 member of RAST email : hs1jan(a)tamsat.org _______________________________________________ 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

1 0

Re^2: Satellites List
by Mineo Wakita 09 Aug '13

09 Aug '13

Hello Clint/K6LCS, Jeff/NX9B, and all. Please tell me if you notice the mistakes or errors in my list. I have summarized in my web site for the latest Satellites information. These are the result of the communication with the radio amateurs around the world via Satellites. Please refer to them. Thank you all. --------------------------------------------- Name: Mineo Wakita / JE9PEL, JAMSAT member Mail: ei7m-wkt(a)asahi-net.or.jp URL : http://www.ne.jp/asahi/hamradio/je9pel/ QTH : Yokohama Japan, GL: pm95tj Date: 9 Aug 2013 ---------------------------------------------

1 0

Fw: Delfi C3 Close Approach Notification
by Peter Portanova 08 Aug '13

08 Aug '13

Subject: Delfi C3 Close Approach Notification Sir/Ma'am, The United States Joint Space Operations Center (JSpOC) has identified a predicted conjunction between Delfi C3 (SCC# 32789) and SCC# 31066. Primary Object: Delfi C3 (SCC# 32789) Secondary Object: SCC# 31066 Time of Closest Approach: 11 AUG 2013 1:43 UTC Overall miss distance: 190 meters Radial (dU) miss distance: 183 meters In-Track (dV) miss distance: -4 meters Cross-track (dW) miss distance: -52 meters Primary Radial Error (U): 14 meters Primary In-track Error (V): 918 meters Primary Cross-track Error (W): 12 meters Secondary Radial Error (U): 57 meters Secondary In-track Error (V): 2607 meters Secondary Cross-track Error (W): 41 meters Very Respectfully, JSpOC Orbital Protection Team Joint Space Operations Center Vandenberg Air Force Base, California USA NO WARRANTIES: The United States provides the enclosed Space Situational Awareness (SSA) services or information "as is" and makes no warranty, either express or implied, as to the condition or suitability of the information and services, nor its fitness for a particular purpose. IMMUNITY: The United States, any agencies and instrumentalities thereof, and any individuals, firms, corporations, and other persons acting for the United States, shall be immune from any suit in any court for any cause of action arising from the provision or receipt of SSA services or information, whether or not provided in accordance with 10 USC 2274, or any related action or omission.

1 0

Re: Non-mechanical Azimuth/Elevation Feedback Advice
by Zach Leffke 08 Aug '13

08 Aug '13

All, Thanks to everyone that has responded both on and off list. For my first attempt at finding a non-mechanical solution I plan to use the MEMS accelerometer (for El) and magnetometer (for Az) solution. When still exploring the Potentiometer solution, because of space requirements and other factors I was pricing out multi turn potentiometers. For the gearing ratios I needed, I required about a 5 turn potentiometer, which at least according to digikey and the quick search I did, priced to about $20.00 apiece. The MEMS Magnetometer (HMC5883L) and Accelerometer (MMA8452Q) each price out to less than $20.00 each on sparkfun, so I'll actually be saving a few bucks. That's the plan, at least for the first iteration. We'll see how it goes! Thanks again to everyone! Go Team AMSAT! -Zach, KJ4QLP

1 0

slightly off-topic - TerraTec dongle - SDR Sharp
by Philip Jenkins 08 Aug '13

08 Aug '13

I've seen references to this floating by on the BB, and I know some of you are experimenting with it, so I offered to post this for a local ham (who is not on this BB) who is having trouble installing this dongle. I don't have one myself - just posting for him - so please contact him directly. Thanks Philip N4HF ----------------------------------------------------- Harry, KD4OQQ, hlrice(a)att.net, says that his is a TerraTec Plus, which he can't find listed on the SDRSharp website. He has watched several YouTube videos about installing, and read the documentation, but with no success. He says that none of the LEDs are lighting, no matter what he does. He's wondering if the dongle itself is bad, so please contact him and help him with the troubleshooting.

2 1

Re: Satellites List
by Clint Bradford 08 Aug '13

08 Aug '13

>> ... I believe that you owe Mineo a very sincere apology ... Then my writing was poor. And for that I do, indeed, apologize for. I actually thought so much of that document that I added a link to it on my references page of my Web site. I was just trying to relate back when I first started to have an interest in a specific aspect of the hobby, and started wandering the 'Net, and getting conflicting info and - worse - outdated info to try to sift through. As I wrote, that is a valuable, historical document. YES, I apologize - it was not meant to demean the historical value of the work. Clint Bradford 909-241-7666 - cell ---------------------------------- Clint Bradford, K6LCS http://www.clintbradford.com

1 0

Re: Non-mechanical Azimuth/Elevation Feedback Advice (Zach Leffke)
by Burns Fisher 08 Aug '13

08 Aug '13

I'm also thinking about an el cheapo rotator based on a pan/tilt base. (In fact search el cheapo rotator for an article about doing the same thing manually). The pan/tilt that I was going to start with does have a "center" command as well as 4 memories where you can remember previous positions. It is based on steppers, not A/C, though. Anyway, I was thinking about programming 4 strategic positions into the memories and using them with "center" to get close to where I want to be, and then send step commands to get more exact. Requires some programming of course, but that's what Arduinos are for! I *like* the MEMS compass idea. Pretty cool! Burns Fisher, W2BFJ

1 0