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{ "url": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/3BRPTCB3CJY32NRL66O52PYZXWS5MQWC/", "mailinglist": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/", "message_id": "[email protected]", "message_id_hash": "3BRPTCB3CJY32NRL66O52PYZXWS5MQWC", "thread": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/thread/BPTPJPOYK62QAVPE7C2NBM4KL3PRWDEV/", "sender": { "address": "gordonjcp (a) gjcp.net", "mailman_id": null, "emails": null }, "sender_name": "Gordon JC Pearce MM3YEQ", "subject": "[amsat-bb] Re: Help for Humber College Students with ISS Contact", "date": "2008-11-26T10:13:44Z", "parent": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/BPTPJPOYK62QAVPE7C2NBM4KL3PRWDEV/", "children": [], "votes": { "likes": 0, "dislikes": 0, "status": "neutral" }, "content": "Ken Owen wrote:\n<snip>\n> From: Paul Je [mailto:[email protected]] \n> Sent: Monday, November 24, 2008 1:17 PM\n> To: Ken Owen\n> Subject: RE: ISS contact\n> \n> Say Ken, we've set up our primary station just fine, but I was wondering if\n> I could ask for your advice. Well, you see, we've tested the transceiver\n> that we have (the ICOM IC-V8000), and we can transmit and receive just fine\n> with it on our circular-polarized HyGain 2m antenna. Also, we did a VSWR\n\nWhat kind of antenna? Anything more than a 3-element Yagi will be more \ntrouble than it's worth. Bear in mind that I've successfully sent and \nreceived APRS with the ISS using a homebrew vertical. The higher the \ngain of your Yagi, the more directional it is, and the more accurately \nit needs to be pointed. I find that a 3-element beam is okay for \nhandheld use when working portable, and has more than enough gain to hit \nthe amateur satellites with 5W from an HT.\n\n> test and our loss is minimal with the 75W transceiver that the ICOM\n\n75W sounds a bit much, especially into a very directional antenna. \nYou're trying to talk to the ISS, not etch your name on the side.\n\n> produces. Ok, so here's the problem. Even with all the proper testing\n> done, we still can't seem to pick up or hear the 166MHz beacon that the ISS\n> produces.\n\nAre you using a 166MHz aerial for this? Are you sure the beacon is even \ntransmitting when you think it is? Your high gain Yagi might well be \nvery very deaf outside its intended band. Try making a simple dipole or \neven a two-element beam for 166MHz. With two elements, it will have a \nmore-or-less cardioid pattern, so you shouldn't really even need to \nsteer it much ;-)\n\n> My classmates and I are a bit worried/stressed out. I mean, just on last\n> Friday, we did a test and someone drove at least 5km away from out college\n> and heard us fine with the handheld radio he had. We had a signal strength\n> of 3+ out of 5. He could've drove out even further, but we felt that we did\n> enough testing to know that any attenuation losses were very minimal. \n\nThe ISS is pretty much the classic case of line-of-sight. There's \nnothing in the way, and it's only 200 miles away. There's nothing to \nstop the signal anywhere.\n\n> Well, do you know what the problem could be? Have you heard the beacon?\n> What does it sound like? Maybe we should delay or advance the rotor by a\n> few seconds? We're using NOVA software, and it allows us to send our\n> transmission a few seconds ahead or behind. \n\nUse a wider beamwidth.\n\n> Ok, so we have a circular polarized HyGain antenna hooked up to our Yaesu\n> G5500. Uhm, this might sound dumb but do you know whether we should be\n> right hand circular polarized or left hand circular polarized? Is the ISS\n> right hand or left hand on 144.490MHz? \n\nThis I'm not sure about. I thought about building a circular polarised \nantenna for ISS and amateur satellite work, but it seemed more trouble \nthan it was worth. If you've got the polarisation wrong, it will be \nincredibly deaf!\n\n> I'm trying to research this, but I'm having the hardest time to find this\n> information out. Oh, also, since our antenna is circular-polarized, does\n> the way we set our antenna have an effect on our transmission? I know this\n> sounds confusing, but let me explain:\n> \n> If you looked at our antenna from the front so that you could see all the\n> dipoles/elements both vertically and horizontally to your view, well, should\n> they be perfectly aligned with one set horizontal and one vertical? Both\n> the vertical and the horizontal are perfectly 90degrees to each other,\n> however, instead of being a perfect cross to your view, the elements are\n> more like an \"X\" to your point of view (even though both are perfectly\n> 90degrees to each other).\n\nThat shouldn't make much of a difference. Imagine the signal arriving \nlike a big corkscrew - the key to the circular polarisation is that the \nsignal arrives at one set of elements and then a quarter wavelength \nlater arrives at the second. Now, let's imagine we've made our \ncircular-polarised aerial by putting two dipoles on a boom, 1/4 \nwavelength apart, and connected them by two equal-length lines. The \nvertical one is at the \"front\" of the boom and the horizontal one is to \nthe \"back\", and the up and left elements of the dipoles are \"hot\".\n\nLet's pause reality just as a \"vertical\" peak hits the vertical dipole. \n That dipole now has some signal. Using the single-Planck-time advance \nbutton on our Worldivo (it's like a Tivo for the fundamental nature of \nthe Universe), we'll step through - tick, tick, tick, tick - until a \nquarter wavelength has passed. Now the vertical peak is somewhere above \nthe centre of the horizontal dipole - it's picking up no signal - and \nthere's a horizontal peak about the centre of the vertical dipole - no \nsignal there either.\n\nStep forwards another quarter wave, and there's a vertical dip at the \ncold end of the vertical antenna, and the horizontal peak we just saw \ncame in is at the hot end on the horizontal antenna. We now have a \nnegative signal on the cold side of the antenna connection (remember, \nboth dipoles are effectively in parallel) and a positive signal on the \nhot side of the antenna connection - loads of signal!\n\nIf we reversed the direction of the corkscrew, or reversed the phase of \n*one* of the dipoles, then the two signals would cancel out almost \ncompletely. You can have two signals transmitted in left and right \ncircular polarisation on the same frequency, and have *phenomenal* \nrejection between the two.\n\nI should point out that there's quite a lot in that explanation that's \nnot entirely true, or at least terribly inaccurate. It's still a useful \nmodel for getting your head around what seems at first to be a very \nconfusing polarisation mode.\n\nHTH,\n Gordon\n", "attachments": [] }