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{ "url": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/2PVONRXQJLOAN6I446YSVVX4MDBLORPO/", "mailinglist": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/", "message_id": "CABGf72pWfVyT7_=o1e+2o2mwyXWthb=0tcBpydnSV+UCeHxPrg@mail.gmail.com", "message_id_hash": "2PVONRXQJLOAN6I446YSVVX4MDBLORPO", "thread": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/thread/FJT3YR7OCJMHVBS5SAYGFXWTBD5K6IAY/", "sender": { "address": "tosca005 (a) umn.edu", "mailman_id": null, "emails": null }, "sender_name": "John Toscano", "subject": "Re: [amsat-bb] Link budgets for upcoming HEO/GEO sats", "date": "2016-04-09T22:34:10Z", "parent": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/FJT3YR7OCJMHVBS5SAYGFXWTBD5K6IAY/", "children": [ "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/HAMJHISAYENF3BMYJIONZJUBHJ23X7MY/" ], "votes": { "likes": 0, "dislikes": 0, "status": "neutral" }, "content": "Estimates suggest aiming for 8 watts of RF and a re-purposed\n3-foot-diameter satellite TV dish to be able to get into the bird. It would\nbe nice if only 3 - 4 watts were enough to do the job, because there are\ninexpensive 3 - 4 watt linear amplifiers designed for First Person Video on\nradio-controlled \"drone\" aircraft like this:\n\nhttp://www.ebay.com/itm/262249565979?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT\n\nSo, time will tell. It is possible that with a slower digital transmission\nrate the bird might hear well enough for the lesser power. I expect I will\ntry one of these low-power amps, and might even consider driving a pair of\nthem into an appropriate combiner to get twice the power if one by itself\ndoes not make the grade. They are small and light, but would require\nprotection from weather. On the other hand, I should have 10 watts\navailable if I need it, once I perform these modification on a much bigger\nand heavier surplus power amplifier:\n http://www.g4fre.com/avantekpa.htm\n(In fact, I have two of these beasts awaiting modification. I think they\nare much too large and heavy for my tripod-mounted rover station, but one\nof them might be doable on a fixed station.)\n\nIt would be hard to equal the gain of a dish by using a helix. Once upon a\ntime, I thought that the helix was the greatest antenna in existence, just\nmake it longer and longer to get outrageous amounts of gain. But the more I\ninvestigated the less excited I got about building a humongous helix\nantenna. (In fact, at one point, I was dreaming about a 2x2 quad array of\nhelices of great length, but I never actually attempted to build one.) On\nthe other hand, I have been amazed by the ability of a scrap-heap satellite\nTV dish (less than 3 feet in diameter) and a couple of watts of power to\nmake terrestrial 10 GHz SSB QSO's over distances of well over 100 Km, at\nleast when I stopped using a dish that was bent like a Pringles Potato\nChip, causing it to lose 10-20 db of its gain! I expect even greater things\nwhen an un-damaged dish is pointed up into the sky, away from trees and\nhills!\n\nFor the 10 GHz downlink, a possible low-cost scenario might work out to be\na direct-to-home satellite TV dish of approximately one meter in diameter,\nand a PLL-based LNBF, which would mix the 10.5 GHz satellite signal down to\nthe 600 MHz or so range, and the receiving that with some sort of SDR,\npossibly even a RTL-SDR USB dongle, though perhaps a better SDR might be\nrequired. The downlink is going to be DVB-S2x which is NOT the native\nformat of the inexpensive USB dongles. DVB-S2x requires a bit of\ncomputation ability on the computer controlling the SDR, especially if the\nVLSNR (Very Low Signal to Noise Ratio) extensions are needed. It is also\npossible that we can find (and suitably modify) an inexpensive\ndirect-to-home satellite TV receiver. AMSAT also expects to have a familiar\nUSA company building complete ground station transceivers, but those will\nlikely command a bit of a (well-deserved) premium price. We are actively\npursuing a lot of different choices, so stay tuned!\n\n>From what I have heard, the bird will be in a geosynchronous orbit, NOT a\ngeostationary orbit, so periodic dish re-positioning of some sort will be\nnecessary. Since the primary payload onto which we get to piggyback is\nowned by a government agency that likes to keep secrets, an exact proposed\norbit is not widely discussed, if at all. So it is hard (for me, at least)\nto give more specifics at this time. You won't need the\nhorizon-to-zenith-to-horizon pointing ability needed to chase a satellite\nin Low Earth Orbit, but some positioning in both azimuth and elevation will\nbe needed. High precision will be more valuable than a wide range of\npointing directions. In other words, being able to tweak the position by a\ndegree at a time to fine-tune the pointing would be more helpful than being\nable to move the dish by 30 or 40 degrees. I wish I could be more specific,\nbut I can't at this time. On the other hand, one of the other projects in\nthe works is the NASA-sponsored CubeQuest Challenge, and for that bird you\nwould need to be able to point at any part of the sky where you observe the\nmoon, since the package is going to be headed for lunar orbit! We are\ntrying to make these two birds compatible with the same ground station\nequipment.\n\nSorry for the vagueness, but I hope it helps a little bit.\n73 de W0JT/5, EL09vu\n\nOn Sat, Apr 9, 2016 at 12:42 PM, Jim Barbre <[email protected]> wrote:\n\n> Hi all,\n>\n> Given that people are currently working on groundstations for the\n> upcoming HEO/GEO sats, I am in hopes that at least some of the following\n> questions can be answered.\n>\n> What kind of power will be required on the 5GHz uplink?\n>\n> Does anyone currently make a linear amp or upconverter that can be mounted\n> at the antenna for the 5GHz uplink?\n>\n> Will I be able to use a helix antenna on the uplink or will I be limited\n> to using a dish?\n>\n> Same question with regards to antenna usage for 10GHz downlink.\n>\n> What size dish?\n>\n> With AO-10 and AO-13 I could point my antennas at the satellite and not\n> have to move them for an hour or longer. These new sats will be using\n> microwave frequencies. What kind of realistic expectation do I have of\n> being able to point a dish at the satellite before having to tweak it?\n> Otherwise said, will a rotator be absolutely necessary?\n>\n> Thanks for the info. Looking forward to working the next generation of\n> HEO/GEO sats.\n>\n> 73\n> Jim Barbre\n> KB7YSY\n> _______________________________________________\n> Sent via [email protected]. AMSAT-NA makes this open forum available\n> to all interested persons worldwide without requiring membership. Opinions\n> expressed\n> are solely those of the author, and do not reflect the official views of\n> AMSAT-NA.\n> Not an AMSAT-NA member? Join now to support the amateur satellite program!\n> Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb\n>\n", "attachments": [] }