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{
    "url": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/DYVKHUCXZY3HQFTHZRL3GIXPLIE25L5O/?format=api",
    "mailinglist": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/?format=api",
    "message_id": "[email protected]",
    "message_id_hash": "DYVKHUCXZY3HQFTHZRL3GIXPLIE25L5O",
    "thread": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/thread/VRKTM7EDUTR4NNI4FLSNWH5VAHCZDHTB/?format=api",
    "sender": {
        "address": "matthew (a) mrstevens.net",
        "mailman_id": "9211e31bd97d4743ace6c47863af3e1b",
        "emails": "https://mailman.amsat.org/hyperkitty/api/sender/9211e31bd97d4743ace6c47863af3e1b/emails/?format=api"
    },
    "sender_name": "Matthew Stevens",
    "subject": "Re: [amsat-bb] Observations on AO-91 AFC",
    "date": "2017-11-26T06:49:51Z",
    "parent": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/VYPM5IFSQ24PXA4ORGUM3IPKRZYXJBUJ/?format=api",
    "children": [],
    "votes": {
        "likes": 0,
        "dislikes": 0,
        "status": "neutral"
    },
    "content": "Update from the 0617z pass just now. Using a D72 and arrow, I tried transmitting adjusted for doppler shift, then changing from that doppler adjusted frequency first to 15khz low, then 10khz, 5, and finally back to the correct frequency. All on a much quieter pass than earlier, only 6 or 7 stations on at this time of the morning.\n\nAt -15khz, I was still easily able to access the repeater. However my audio was extremely muffled sounding, and difficult to understand. Another station on the pass reported it sounding “extremely garbled.” I shifted to -10khz, and got the report back that my audio was clear and understandable. To my ears (full duplex), it still sounded a bit muffled but much better than before. Shifting back to -5khz, and then the approximate correct doppler adjusted uplink, I couldn’t really tell the difference between -5 and 0.\n\nSo, conclusion. The AFC seems to be working as advertised! With a 5w HT and arrow I had no problem getting in on a slow pass even 15khz off freq, albeit with terrible audio. However, while 10khz off was acceptable, +/-5khz was what I would consider “good.”\n\nMy advice is to use the AFC as an aid, not a crutch. Don’t count on it to correct a large tuning error very well, especially on a busy pass with more than one user transmitting simultaneously.\n\nKeep tuning for doppler on your uplink like you have been for AO-85, but don’t worry too much about being exact with it on AO-91. The AFC will “fix” it if you’re off a few kHz.\n\nAs a side note, once again tonight I was hugely impressed with the audio quality, ease accessing the repeater, and horizon to horizon performance of the new sat! Amsat really scored with this one.\n\n73,\n- Matthew nj4y\n\nSent from my iPhone\n\n> On Nov 25, 2017, at 22:52, Scott <[email protected]> wrote:\n> \n> Matt’s observations beg the question of what the design basis of the AFC system might be- single signal or a number of signals of varying amplitude and frequency.\n> \n> In the end it may not matter much, but if understanding better how it works leads to more enlightened use of the bird than a few of the (obviously there’s still learning going on) passes this weekend, it could be very helpful.\n> \n> Thanks for any info or guidance you engineering guys may have, and again, congrats on a super job.\n> \n> 73 Scott ka9p\n> \n> Make something good happen!\n> \n>> On Nov 25, 2017, at 8:09 PM, Matthew Stevens <[email protected]> wrote:\n>> \n>> I’ve done a bit of study on the Fox series AFC. I never really knew\n>> much about it up until this point, but with all the discussion on the\n>> amsat-bb about AO-91’s AFC function, and the alleged lack of uplink\n>> Doppler tuning needed – I figured I should educate myself a bit more.\n>> \n>> I also wanted to test it out some. My observations (which I’ve\n>> outlined in another BB post\n>> http://www.amsat.org/pipermail/amsat-bb/2017-November/065569.html),\n>> making hundreds of QSOs on AO-85 using various antennas, radios, and\n>> power settings have been that there is definite need to tune the\n>> uplink frequency for Doppler shift. My initial experiences working\n>> passes on AO-91 from a few minutes after commissioning, using an HT\n>> and whip, then an HT and Elk, then and HT and arrow, did nothing to\n>> change my mind about tuning for the AO-91 uplink.\n>> \n>> However, even though I already made a bunch of QSOs on AO91, I didn’t\n>> really have enough data to make any kind of real conclusion about the\n>> AFC on AO-91. So, I figured I’d try some experiments and post them\n>> here!\n>> \n>>>> \n>> \n>> Today was the first pass I had worked on AO-91 with anything other\n>> than a 0.05-5w Kenwood D72 HT for a radio. I broke out my Icom 821H\n>> for a 90 degree lunchtime pass, turned up the power to the full ~35w,\n>> and used my handheld arrow II antenna. Having already heard the\n>> absolute zoo that has been daytime AO-91 passes, I was curious first\n>> to hear how it went using more power (as far as being able to get in\n>> over the dead carriers and multiple hetrodyning uplinks), and second,\n>> how the AFC functioned with a lot of high-power users.\n>> \n>> What I found: The AFC *does* seem to work! However, there are some\n>> usage caveats that I have to note. When there is a single signal\n>> coming into the bird, it seems to compensate fine for being off\n>> frequency (within reason). I didn’t try too wide of a tuning range,\n>> since compared to some stations I heard today I didn’t have enough\n>> power to be way off (more on that in a minute). But I did try +/-\n>> about 5khz, and it seemed to compensate just fine if I was the only\n>> signal coming in.\n>> \n>> That’s the rub however. There was virtually no time today where I was\n>> the only signal coming into the bird! And when there was a bunch of\n>> different signals, basically, the strongest uplink was the one that\n>> determined the AFC tuning. You can hear that happening in the\n>> recording which I’ll link to below. There was more than one instance\n>> where I began to transmit over a carrier or other signal that I was\n>> hearing (being careful not to transmit over any actual audible callers\n>> or QSOs in progress). You can hear my audio go from poor to crystal\n>> clear as the AFC (apparently) adjusted to my carrier – and I did not\n>> adjust my transmit frequency at the time. I assume that my signal was\n>> stronger than the others, and the AFC “picked” mine.\n>> \n>> You can also hear a signal from XE3ARV, who had by far the strongest\n>> signal I heard during the pass. Because his uplink signal was so much\n>> stronger than anyone or anything else, it sounded like the AFC\n>> adjusted to whatever his uplink frequency was. If I, or anyone else\n>> was transmitting at the time, you can hear it IMMEDIATELY go from the\n>> other clear (or scratchy) signal (depending on what state the AFC\n>> tuning was in at the time), to a crystal clear downlink from XE3ARV.\n>> \n>> Another observation of note was the downlink signal from 5K0T. At the\n>> beginning of the pass you can hear a very clear signal from their\n>> obviously strong uplink. As the pass progressed, the audio quality on\n>> their downlink deteriorated a lot. The only reason I can see for this\n>> is that they may have not been adjusting for Doppler during the pass,\n>> and were possibly 10khz or more from the correct uplink frequency\n>> (perhaps transmitting at 435.240 the entire pass?). I can’t confirm\n>> this as I wasn’t there to see what was happening on their end, but\n>> that is one possible explanation to why their signal sounded like it\n>> did at the end of the pass. This hypothesis also is supported by\n>> having heard another station on a much quieter, early morning pass the\n>> other day who I know was transmitting 30khz off frequency. His audio\n>> sounded very similar to 5K0T at the time.\n>> \n>> Yet another observation is that when there are a lot of users on the\n>> pass, it seems to be beneficial to adjust for Doppler. There were\n>> several times during today’s pass where I did tune my radio to the\n>> correct, Doppler adjusted uplink frequency. If there was a high level\n>> of QRM, tuning for Doppler seemed to help my signal be received by the\n>> satellite, as opposed to tuning +/- 5khz from the Doppler adjusted\n>> value.\n>> \n>> Here is my recording:\n>> https://drive.google.com/open?id=1c8XYCoxFCKCyR4dtfwJCyM9tjfo1mLKd\n>> \n>> TL;DR observations:\n>> \n>> 1. AFC does work within some limitations.\n>> \n>> 2. With multiple strong signals into the bird, the strongest “wins” as\n>> far as determining the AFC adjustment. This makes other signals tuned\n>> to other frequencies sound “staticky”\n>> \n>> 3. Transmitting very far off frequency makes your downlink audio sound bad.\n>> \n>> 4. Adjusting for Doppler seems to help your signal capture the sats\n>> receiver better than other users who are operating at a similar power\n>> level to you.\n>> \n>> Conclusion so far: In practice, AFC is good for correcting minor\n>> Doppler tuning errors. However, unless there is only one user\n>> transmitting into the sat at a point in time, it does not eliminate\n>> the need to tune your uplink for Doppler.\n>> \n>> I would be curious to hear other observations and interpretations from\n>> AO-91 passes. I think it’s helpful to support observations with\n>> recordings, so others can listen and draw their own conclusions about\n>> your interpretation of what has occurred.\n>> \n>> Also, these are just my initial impressions from operating passes…and\n>> these are subject to change over time :-)\n>> \n>> \n>> \n>> 73,\n>> \n>> Matthew nj4y\n>> _______________________________________________\n>> Sent via [email protected]. AMSAT-NA makes this open forum available\n>> to all interested persons worldwide without requiring membership. Opinions expressed\n>> are solely those of the author, and do not reflect the official views of 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",
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