Amsat-dc (INACTIVE) March 2013

7 participants
6 discussions

inquiry about homebrew az-el systems
by Samudra Haque 28 Mar '13

28 Mar '13

Hi, about two years ago, I started a design for a robotics class project of a AZ-EL rotator controller system, and a hardware package for the mechanism for rotating an antenna in any direction subject to mechanical stops. The system would have been able to handle regular and flip modes. I didn't do anything more than calculations, and moved on to building a classroom instructional robot then. Lately, as I am setting up (K3GWU, the George Washington University Amateur Radio Club and Research Station) I find that the price of az-el systems such as G5500 + Yaesu AZ-EL rotors are expensive, and are not typically available on an affordable basis on Ebay or eham.net etc. Well, of course, expensive is a relative term, for a student hobby organization, it's a lot, and I guess for small ham operators it is also moderately expensive. This may be a frequently asked topic: does any one have experienced with (tested) kit designs for AZ-EL rotors that can be made with parts from current suppliers ? I know there are a number of controller designs, but I am interested to know if there are any options for suppliers of the required gears/motors etc. I have located several large AC motors / DC motors at my university mechanical engineering workshop, but they are not all guaranteed the same specs. I now realize if I do embark on a actual design process with my model/simulation/hardware, it would be nice to build several of these all at once to share the development cost over the production run, and ensure those who want a cheap AZ-EL system can get one. Otherwise the production cost of one heavy duty system is going to be quite high. I hope some of you may have suggestions for me, both (+) and (-) or perhaps (~) in nature. I thought amsat / amateur radio folks have a common need to encourage homebrew activity to keep their brain cells in working condition? I'm opening this question up to the national US audience, and welcome any discussion on the challenges of making the ever-so-important azimuth-elevation rotor. I've studied some of the alternatives: Alliance U100 and Yaesu G-5500. I think we can do better in 2013. But ideally, to allow the wide adoption of AMSAT ground stations, what price point would the system have to be to make it worth building ? 73 de N3RDX George Washington University

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Thank you & antenna links
by Stephan Greene 25 Mar '13

25 Mar '13

All: I had a great time at the AMSAT-DC meeting on Saturday. I greatly appreciated the contributions, ideas, and questions from all the participants. HUGE THANKS to Pat Kilroy and to NASA GSFC for hosting! Since I went on quite a bit about cheap antennas, here are some links to design & construction info and some related information. Cheap Antennas for the AMSAT LEO's (WA5VJB) http://www.wa5vjb.com/references/Cheap%20Antennas-LEOs.pdf Construction suggestions, tuning, diplexer design. Also discusses performance of Arrow antenna. Cheap Yagi for 70 cm (search Amsat.org or internet for the companion 2M design) - uses foam board! http://www.amsat.org/amsat-new/information/faqs/crow/JulAug06AmsatJournal.p… Controlled Impedance "Cheap" Antennas (WA5VJB) http://www.wa5vjb.com/yagi-pdf/cheapyagi.pdf The original cheap yagi article. Designs for 2M, 220 MHz, 70cm, 902 MHz, 1296 MHz, including AMSAT and FM sections on 70cm. Great ideas for terrestrial as well as satellite ground station antennas. The 6 element 2M antenna I had with me on Saturday is VJB's 2M design and I've used it with reasonable success on 2M terrestrial (tropo, E-skip) and meteor bounce (FSK441 using WJST software). It's probably about as large as I'd want to use for a VHF rover station or portable installation. It's larger than necessary for use with LEO satellites; a much lighter boom & 3 or 4 elements are more than sufficient. There have been several published handheld designs that are 2 elements, and the Arrow (even with alleged performance issues) is a 3 element design. WA5VJB Herringbone Log-Periodic for satellites: http://www.cq-vhf.com/vhf_highlights/2012_vhf/2012_spring_vhf/2012_spring_v… Interesting design, simple, very portable (designed for hand-held). DK7ZB's designs. http://www.qsl.net/dk7zb/start1.htm Huge wealth of information here! Probably better performance than the WA5VJB designs, but more demanding of precise construction. Most of his designs are in metric units but some have English measurements as well. There are several standard inch dimension rods that are close enough to metric sizes to work. And you can get metric-dimensioned components , too. Many examples of ingenious construction techniques in the photos. His area of interest in terrestrial weak-signal communications; many of his designs are VERY optimized for 144.2 MHz and 432.2 MHz, particularly the lower impedance designs. So stick with the smaller 50 ohm designs for satellite use. The 2M/70cm-Yagis Ultralight page is probably most useful for satellite antennas. http://www.qsl.net/dk7zb/PVC-Yagis/PVC-details.htm Many of the designs are available from SOTABeams (UK) http://www.sotabeams.co.uk and as kits from Attila Kocis DL1NUX, Nuxcom, http://www.nuxcom.de. Some satellite-specific ideas & info: http://www.qsl.net/dk7zb/Cross-Yagi/crossyagi.htm Using electric fence post insulators as element mounts (especially for aluminum booms) http://www.qsl.net/dk7zb/images/Elementhalter/elementholder_fence.htm DK7ZB and WA5VJB both assume the antenna elements are insulated from the boom. If you use an aluminum boom (recycled antenna pieces, ¾"x ¾" extrusions from Lowes/Home Depot), you have to mount the elements above the boom or with insulated plugs through the boom (and worry about boom correction factors). These insulators are a good alternative. And I don't understand why the Europeans get all the cool design small parts. Less exotic looking ones are available on Ebay & Amazon (and probably at farm/horse supply stores, Tractor Supply, etc.). I purchased a big bag of them off Ebay and plan to experiment with this approach. Antenna element materials: WA5VJB recommends welding rod (cheap, elements may require splicing with hobby tubing to get lengths for 2M), #10 solid copper wire ($$), solid aluminum guy wire (old versions - Radio Shack discontinued the product several years ago), hobby tubing/rods (can get $$). Several online vendors sell a variety of aluminum rod and brass rod, some will cut to custom length at small additional cost if you are as inept as I am with hand tools! Watch shipping charges if you go over 48" in length. On the 6 element 2M antenna I displayed, I spliced the 2M driven element for that reason. The local big box stores generally don't stock small enough diameters/long enough lengths but it's worth a look. Or hit Timonium or Manassas and see what's in the flea market. Internet Vendors: http://ww.speedymetals.com http://www.onlinemetals.com (I think I ordered from them) http://www.mcmaster.com/#standard-aluminum-rods/=m17g2q [Thank you to Sambudra for reminding me of M-C] McMaster-Carr sells the rod stock in 6ft lengths; I haven't checked if they have oversize shipping charges. They sell a lot more than just metals. The above designs can make circularly polarized antennas. The 2nd set of elements is mounted at 90 degrees on the boom and is offset by ¼ wavelength (free space, I believe). It's fed in parallel with the 1st set. Since both antennas are 50 ohm designs, there are at least 2 solutions to deal with the parallel impedance: 1. Make a matching harness from coax of carefully cut and assembled lengths. 2. Purchase or build a power divider (both Directive Systems and M2 Antennas sell them), use IDENTICAL lengths of 50 ohm feedline to the antenna feedpoints. Note - According to the Directive Systems website, the company has been sold and is in the process of moving to HAYMARKET VIRGINIA this week! http://www.directivesystems.com RF Connection (therfc.com) in Gaithersubrg MD is an excellent local source of feedline, connectors, couplers, and associated parts. He can also make custom harnesses (those phasing lines). Attends all the local hamfests, so good way to save on shipping large amounts of coax across the country. I did not discuss omnidirectional antennas. The quadrafiller helix and Lindenblad were mentioned at the meeting, and Pat had a Lindenblad on display. These antennas have a reputation as difficult to build. A passive Lidenblad design was published in QST (or maybe AMSAT journal) a few years ago and looks much easier to build. No idea how well they actually perform. The local RF noise level is high enough that higher-gain antennas may be a requirement around the DC area. WB4APR has recommended for years using a low-moderate gain yagi elevated 15 degrees (some folks go for 20). Rotate in azimuth and don't worry about elevation - most passes are not close to overhead and the satellite spends very little time there. And when it is close, the shorter range and path loss make up for the loss in antenna gain (at least for smaller antennas - a very tight EME array is a different matter!) Preamps - besides the wideband RX-only model AMSAT sells, there are several sources mentioned on Saturday. Advanced Receiver Research's product list is here http://www.advancedreceiver.com/page2.html Hope this is of use to folks and look forward to the next meeting & meeting you on the air locally, and on the birds! 73 Steve, KS1G FM18 Herndon, VA -- ----------------------------------------------------------------------------------------------------------------- Steve Greene ks1g04(a)gmail.com <kay ess one gee zero four>@gmail.com -----------------------------------------------------------------------------------------------------------------

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ezcap SDR receiver and GNU Radio
by David Bern 24 Mar '13

24 Mar '13

Friends: At the AMSAT-DC Workshop on Saturday, March 23, 2013, Tom, K3IO and I demonstrated the ezcap $20 RTL-SDR SDR receiver USB dongle with GNU Radio. The ezcap device can be purchased from http://dx.com/p/mini-dvb-t-digital-tv-usb-2-0-dongle-with-fm-dab-remote-con… The January 2013 issue of QST discusses the ezcap USB dongle on pages 30 to 35 in an article /Cheap and Easy SDR. /In addition, more information is at http://rtlsdr.org/ http://osmocom.rtlsdr.org/ At the Sunday Seminar of the 2012 Digital Communications Conference, a custom Ubuntu Linux DVD-ROM with GNU Radio pre-installed on it was distributed http://dl.dropbox.com/u/17338050/xubuntu-gnuradio.iso http://dl.dropbox.com/u/17338050/xubuntu-gnuradio.jpeg The GNU Radio home page is at http://gnuradio.org/redmine/projects/gnuradio/wiki A .grc file defines a GNU Radio configuration. .grc files for narrow band FM and for wide band FM are at http://dl.dropbox.com/u/17338050/mono-nbfm-ctcss.grc http://dl.dropbox.com/u/17338050/mono-fm-and-sca.grc These can be used to listen the weather radio or to an FM repeater and an FM broadcast station, respectively. We need to thank my SDR and DSP guru Chris, KB3CS for providing these .grc files. After you have booted the DVD-ROM, copy these .grc files to your desktop. Then, double click on a .grc file and gnuradio-companion should start up with a dataflow diagram. Click on the gray gears icon to execute the .grc file; be sure to increase the audio volume as necessary. I will remove these files in two weeks to free up space in my Dropbox. For those who have a Hermes SDR, Tom McDermott, N5EG has been working with GNU Radio for the Hermes SDR transceiver http://svn.tapr.org/repos_sdr_hpsdr/trunk/N5EG/ I have not tried this yet, so I cannot comment on this. Enjoy, David, W2LNX

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link
by james woods 18 Mar '13

18 Mar '13

http://migma.su/fej/raypatybbrvgd/xwcnrmdsx=plthsyfw

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A Radical Concept & Challenge
by Pat Kilroy 10 Mar '13

10 Mar '13

AMSAT-DC Workshop: http://patkilroy.com/amsat-dc/ I HAD A RADICAL IDEA for a fellow AMSAT member who reads this message, to make it his or her own, and run with it. . . . WHAT IF we have a *great* turn out for our Spring Workshop and are "burdened" with either too many hardware setups overflowing the VC auditorium or too many non-hardware- toting attendees (i.e., lots and lots of non-AMSAT members)? . . . WHAT IF someone runs a Sat Pass List for our location for all amateur and Wx satellites on our workshop date? . . . WHAT IF the weather on Saturday morning, March 23, turns out to be an outrageously beautiful day? . . . THEN, wouldn't it be awesome if one of us were to set up a "fully functioning" (you define) portable satellite ground station outdoors immediately outside the VC audi- torium to actively attempt receptions, and perhaps some two-way contacts as well?!! THINK of the possibilities! THINK of the potential benefits! That extra touch would certainly be "News at 11" material. Thoughts? Any takers? Cheers, Pat Kilroy, N8PK AMSAT-DC Workshop: http://patkilroy.com/amsat-dc/ P.S. If you haven't noticed yet, the exact location in mind is shown in two of the photos displayed on the AMSAT-DC workshop Web page. ###

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Coming Soon: AMSAT-DC Spring Workshop 2013
by Kilroy, Patrick L. (GSFC-5680) 08 Mar '13

08 Mar '13

Dear fellow AMSAT members, Please go to http://patkilroy.com/amsat-dc/ and read everything top to bottom. Then please let me know if you have any comments, questions, recommended edits or anything else before I send it off to be published in this weekend's ANS bulletins. This is our workshop. Only a couple weekends away. I hope you can attend. SOME NOTES 1. We are looking for someone to bring a UHF signal source for test purposes for the day, something more substantial than an FM handheld transceiver if possible. A simple analog SSB transmitter in very low power mode looping a recorded voice message would work, and be pretty cool too. Takers, any one? Please contact me. 2. BRING YOUR CAMERA. Free WiFi. 3. We still need volunteers for this event. The task list is quite similar to those of our previous seminars and workshops (see Archives). This event is run by volunteers for volunteers. For example, two AMSAT greeters are needed. Also, a video person with lights, a video editor person, a food organizer, a Net Control Station for talk-in, go-fers, clean up crew for examples. (I believe Art Feller is going to bring his nice big dSLR still camera and gear, so we are covered for publish-ready type still photos.) 4. We need to get the word out. Can you pass the word and the amsat-dc Web page URL to your club news- letter or on a Net? Talk it up on your repeater? Tell a college kid? (YES!) Who knows how to get an event announced on Newsline? On the MDC section Web page and newsletter? Please do! 5. Have you registered through Martha yet? (Please call her even if you only "might" make it: Unlike local hamfests where you can walk right in, THERE WILL BE NO registration on the day of the event!) THANK YOU for your support. We will have a great time! Cheers, Pat Kilroy N8PK

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Amsat-dc (INACTIVE) March 2013