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{ "url": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/4UFJKIV4GIU2LKGSQIP4PRJJZSYU5ETF/", "mailinglist": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/", "message_id": "CANq+eyXsA36RK96zJu5oUZS8N6xGcQ1m5dkrO5izrgthFTGexw@mail.gmail.com", "message_id_hash": "4UFJKIV4GIU2LKGSQIP4PRJJZSYU5ETF", "thread": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/thread/KL4ZLEHBFWQFO44PXWSCND2L7QLWLEOA/", "sender": { "address": "dave (a) druidnetworks.com", "mailman_id": "3b01b396750a47f287ea0c65babd40ea", "emails": "https://mailman.amsat.org/hyperkitty/api/sender/3b01b396750a47f287ea0c65babd40ea/emails/" }, "sender_name": "David Swanson", "subject": "Re: [amsat-bb] Opinions on improving receive for portable ops", "date": "2017-03-10T19:35:13Z", "parent": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/KL4ZLEHBFWQFO44PXWSCND2L7QLWLEOA/", "children": [], "votes": { "likes": 0, "dislikes": 0, "status": "neutral" }, "content": "OK - Couple different things going on here. I'll take your questions\nliterally first then go from there:\n\n1) Maybe - A good preamp can help radios like FT8x7 because they don't have\nthe best noise figure, compared to purpose built VHF/UHF rigs like\n821/910/9100. You would probably get some improvement by adding in a\nquality preamp (like a ARR or a HSM) without even touching the feedline.\n\n2) No. The AMSAT broadband pre-amp is ok for capturing telemetry, or\namplifying signals over a long coax run, but in a short run it doesn't do\nanything to the already weak signals you're receiving from a bird close to\nthe horizon. If you wanna go the pre-amp route, a high quality purpose\nbuilt 70cm is the way to do it.\n\n3) Yes and no.. probably no. The best thing you can do with your yagi is\nto adjust the polarity on the fly, and the best way to do that is by\nholding it. Get it off the tripod, hold it in your hand, and listen to the\nsignal. Rotate it until the bird sounds like it's right next to you. I've\nseen guys with 4 elements and a good location (more on this in a second)\nwork FO29 all the way to -1.0° easy copy. If you're not capable of holding\neverything up, and are using a tripod, make sure it's the kind that you can\ntweak polarity fast with, by rotating on the longitudinal axis. It's not as\ngood as holding it in your hand, but it'll do. If you're constantly\ntweaking your linear polarity, no need to do the CP thing.\n\nNow, reading between the lines on some of the questions:\n\nYou didn't ask the question, but since you said portable I have to mention\nthis. The absolute best tool you have at your disposal once you've freed\nyourself from the shackles of a fixed QTH is LOCATION. I'm going to say it\n2 more times because it's that important. LOCATION. LOCATION. By choosing\nwhere you setup your station, you can get somewhere at a higher altitude,\nclear of obstacles like trees and buildings, and away from artificial RFI.\nBy doing this not only can you actually get true line of site to the\nhorizon, where the bird will be for those long distance passes, but you'll\nhave the best SNR when you do finally hear it. Large parking lots work\npretty good (think Churches or Walmarts) Mountain tops, scenic overlooks,\nheck even balconies or rooftops. If you're truly portable go somewhere that\nyou can see the horizon and is away from the noises a home. When i'm using\nmy portable setup in my backyard I'm lucky if i can hear most birds below\n10°. When I drive 15 miles to the top of a nearby mountain, my portable\nsetup is good to -1.5° and I break distance records. The only thing that\nchanged was the location. Whenever you start talking portable, you're\ntalking location - and location is bar none the most important factor that\nyou have control over when you're talking about improving reception.\n\nAlso, use the absolute best feedline you can afford, that is convenient for\nyour setup. I use 8' of Times (genuine) LMR240 for my portable setup. I\nknow some will use the lmr240uf, or rg8x, or even an off-brand of lmr240,\nbut if you want the absolute best, get the good stuff. LMR400 would be\nbetter yet, but its kinda stiff and heavy, and starts become troublesome to\nuse while portable, hence why LMR240 seems to be the best middle ground,\nfor me and the other solid /P ops. I'm sure someone will be in to tell me\nhow it's only 0.1db less to use 8X or rg58 and other sorts of random\ntheory, but these people will be wrong. Whatever loss you get by\nsacrificing feedline quality will impact your ability to hear at low\nelevations.\n\nFinally cheap yagis are nice. I used them solely for 6 months, and still\nuse them on occasion for guerilla operation... but a commercially built\nportable antenna like an arrow is a good investment for any portable\noperator. Lining up the gain of 2 separate bands on the same boom is a\ndifficult task for most garage builders, and you need all the gain you can\nget for both tx and rx on those <5° passes. Just something to consider.\n\nShout if you have any other questions.\n\n73,\n\nDave, KG5CCI\n\nOn Fri, Mar 10, 2017 at 11:24 AM, Scott via AMSAT-BB <[email protected]>\nwrote:\n\n> I've just started getting on the linear transponders in the last month or\n> so after a 30 year absence from sat work, necessarily with a portable\n> setup,\n> and would be eager to hear experienced opinions on what to do next to\n> improve receive.\n>\n> I'm running Cheap Yagis on V(3 el) and U(6 el), diplexers, about 10 feet of\n> RG8X, and receiving on an FT817 or 897, usually on FO29 and the XW's, and\n> have up to 25 watts available for the uplink.\n>\n> Q's are:\n>\n> 1) with those radios and only about 10 feet of feed line, will a preamp\n> help much on 432?\n>\n> 2) If it will, is the 50$ preamp on the AMSAT site a good start? Or? and\n>\n> 3) With relatively short yagis, will it make a noticeable difference going\n> to circular polarization?\n>\n> WRT to 3, I've pretty much exhausted what I can find the internet, but just\n> don't have a pragmatic sense for what it will do in terms of evening out\n> reception over, say, an FO 29 pass - I read that you nominally lose 3 dbs\n> most all the time but may pick up a lot on the deep fades, but still not\n> sure\n> how that translates to the real world.\n>\n> Or is the answer that the set up is marginal enough I need to do it all of\n> the above if I want reliable communications above about 5 degrees or so?\n>\n> Thanks for the bandwidth and any input.\n>\n> Scott ka9p\n>\n>\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": [] }