{
  "id": 247777,
  "title": "Some domain knowledge questions.",
  "url": "/competitions/seti-breakthrough-listen/discussion/247777",
  "author_name": "Erik Kaufman",
  "post_date": "2021-06-21T05:55:30.969000",
  "votes": 0,
  "comment_count": 6,
  "views": 0,
  "content": "<p>if an FM radio signal is running somewhere in the range containing 88.5 MHz = 88,500,000 Hz and the human hearing range is 20 Hz - 20,000 Hz, how does a radio convert that FM signal to something listenable to the human ear? Is there some decoding going on?</p>\n<p>Within the <a href=\"https://www.kaggle.com/c/seti-breakthrough-listen/overview/data-information\" target=\"_blank\">Data Information section</a>, at the bottom of the picture of the Voyager 1 snippet, I'm having trouble making sense of the horizontal scale.</p>\n<ul>\n<li>How can you calculate relative frequency in Hz from MHz? How can you have a negative frequency value of say -857 Hz? Is this just a standardized scale where we took the range from some amount <code>A</code> in MHz to some amount <code>B</code> in MHz, divided everything in that range by <code>1,000,000</code>, and then finally set <code>0</code> to be the average of <code>A</code> and <code>B</code> and normalized all other values appropriately?</li>\n<li>Shouldn't it be <code>841.9542493</code> MHz instead of <code>8419.542493</code> MHz?</li>\n</ul>\n<p>Last, why must we re-position the satellite every five minutes? Can't we just keep the satellite focused on star A for 15 minutes and watch as the earth continues its orbit and the needle signals change frequency (via Doppler Effect)?</p>",
  "messages": [
    {
      "id": 1359341,
      "postDate": "2021-06-21T08:07:40.180Z",
      "content": "<p>You need to be careful about unit conversions.  88.5 MHz = 8,000,000 Hz  is wrong.  Truth is:</p>\n<p>88.5 MHz = 88,500,000 Hz</p>\n<p>I cannot answer all your questions as I am not an astronomer, but here is one I can answer.</p>\n<blockquote>\n  <p>Within the Data Information section, at the bottom of the picture of the Voyager 1 snippet, I'm having trouble making sense of the horizontal scale.</p>\n</blockquote>\n<p>The scale ranges from 8,419,542,493 + 857 Hz (left) to 8,419,542,493 - 857 Hz (right).  What is counter intuitive is that values decrease from left to right.</p>",
      "rawMarkdown": "You need to be careful about unit conversions.  88.5 MHz = 8,000,000 Hz  is wrong.  Truth is:\n\n88.5 MHz = 88,500,000 Hz\n\nI cannot answer all your questions as I am not an astronomer, but here is one I can answer.\n\n> Within the Data Information section, at the bottom of the picture of the Voyager 1 snippet, I'm having trouble making sense of the horizontal scale.\n\nThe scale ranges from 8,419,542,493 + 857 Hz (left) to 8,419,542,493 - 857 Hz (right).  What is counter intuitive is that values decrease from left to right.\n\n",
      "votes": 2,
      "replies": [
        {
          "id": 1359345,
          "postDate": "2021-06-21T08:10:54.747Z",
          "content": "<p>Thanks for the insight! Will fix the typo</p>",
          "rawMarkdown": "Thanks for the insight! Will fix the typo"
        }
      ]
    },
    {
      "id": 1360051,
      "postDate": "2021-06-21T18:53:15.980Z",
      "content": "<blockquote>\n  <p>Last, why must we re-position the satellite every five minutes? Can't we just keep the satellite focused on star A for 15 minutes and watch as the earth continues its orbit and the needle signals change frequency (via Doppler Effect)?</p>\n</blockquote>\n<p>If a signal is coming from another star system, we can safely assume that the frequency will change significantly over time, but the converse doesn't necessarily hold. (Although the converse might not be such a bad bet with this particular data set.)</p>\n<p>A radio telescope is designed to measure the RF energy coming from a very narrow cone while canceling out any energy coming from different angles. This cancelation isn't perfect. Signals of interest are faint (because of distance) while many RF sources on Earth are strong (because of proximity). Inevitably, some signals from sources on earth leak into the measurements. If an interesting signal from a star doesn't vanish when the telescope points away, it wasn't really coming from that star.</p>",
      "rawMarkdown": "> \n> Last, why must we re-position the satellite every five minutes? Can't we just keep the satellite focused on star A for 15 minutes and watch as the earth continues its orbit and the needle signals change frequency (via Doppler Effect)?\n\n\nIf a signal is coming from another star system, we can safely assume that the frequency will change significantly over time, but the converse doesn't necessarily hold. (Although the converse might not be such a bad bet with this particular data set.)\n\nA radio telescope is designed to measure the RF energy coming from a very narrow cone while canceling out any energy coming from different angles. This cancelation isn't perfect. Signals of interest are faint (because of distance) while many RF sources on Earth are strong (because of proximity). Inevitably, some signals from sources on earth leak into the measurements. If an interesting signal from a star doesn't vanish when the telescope points away, it wasn't really coming from that star.",
      "replies": [
        {
          "id": 1360474,
          "postDate": "2021-06-22T05:51:05.920Z",
          "content": "<p>Thank you! I appreciate your help!</p>\n<blockquote>\n  <p>If an interesting signal from a star doesn't vanish when the telescope points away, it wasn't really coming from that star.</p>\n</blockquote>\n<p>Cool! So the odd-indexed recordings (where the telescope points away) are actually very helpful in determining if an interesting signal is interference or not. The signal is <em>not</em> interesting if the signal is still there in the next off-target recording.</p>",
          "rawMarkdown": "Thank you! I appreciate your help!\n\n> If an interesting signal from a star doesn't vanish when the telescope points away, it wasn't really coming from that star.\n\nCool! So the odd-indexed recordings (where the telescope points away) are actually very helpful in determining if an interesting signal is interference or not. The signal is *not* interesting if the signal is still there in the next off-target recording."
        }
      ]
    },
    {
      "id": 1359879,
      "postDate": "2021-06-21T15:55:58.723Z",
      "content": "<blockquote>\n  <p>how does a radio convert that FM signal to something listenable to the human ear? Is there some decoding going on?</p>\n</blockquote>\n<p>FM stands for Frequency Modulation. Yes, you need to decode it back from its carrier frequency (the 88Mhz)</p>",
      "rawMarkdown": ">  how does a radio convert that FM signal to something listenable to the human ear? Is there some decoding going on?\n\nFM stands for Frequency Modulation. Yes, you need to decode it back from its carrier frequency (the 88Mhz)",
      "replies": [
        {
          "id": 1360475,
          "postDate": "2021-06-22T05:51:30.570Z",
          "content": "<p>Sweet! Thanks for the tip :)</p>",
          "rawMarkdown": "Sweet! Thanks for the tip :)"
        }
      ]
    },
    {
      "id": 1359180,
      "postDate": "2021-06-21T05:55:30.970Z",
      "content": "<p>if an FM radio signal is running somewhere in the range containing 88.5 MHz = 88,500,000 Hz and the human hearing range is 20 Hz - 20,000 Hz, how does a radio convert that FM signal to something listenable to the human ear? Is there some decoding going on?</p>\n<p>Within the <a href=\"https://www.kaggle.com/c/seti-breakthrough-listen/overview/data-information\" target=\"_blank\">Data Information section</a>, at the bottom of the picture of the Voyager 1 snippet, I'm having trouble making sense of the horizontal scale.</p>\n<ul>\n<li>How can you calculate relative frequency in Hz from MHz? How can you have a negative frequency value of say -857 Hz? Is this just a standardized scale where we took the range from some amount <code>A</code> in MHz to some amount <code>B</code> in MHz, divided everything in that range by <code>1,000,000</code>, and then finally set <code>0</code> to be the average of <code>A</code> and <code>B</code> and normalized all other values appropriately?</li>\n<li>Shouldn't it be <code>841.9542493</code> MHz instead of <code>8419.542493</code> MHz?</li>\n</ul>\n<p>Last, why must we re-position the satellite every five minutes? Can't we just keep the satellite focused on star A for 15 minutes and watch as the earth continues its orbit and the needle signals change frequency (via Doppler Effect)?</p>",
      "rawMarkdown": "if an FM radio signal is running somewhere in the range containing 88.5 MHz = 88,500,000 Hz and the human hearing range is 20 Hz - 20,000 Hz, how does a radio convert that FM signal to something listenable to the human ear? Is there some decoding going on?\n\nWithin the [Data Information section](https://www.kaggle.com/c/seti-breakthrough-listen/overview/data-information), at the bottom of the picture of the Voyager 1 snippet, I'm having trouble making sense of the horizontal scale.\n- How can you calculate relative frequency in Hz from MHz? How can you have a negative frequency value of say -857 Hz? Is this just a standardized scale where we took the range from some amount `A` in MHz to some amount `B` in MHz, divided everything in that range by `1,000,000`, and then finally set `0` to be the average of `A` and `B` and normalized all other values appropriately?\n- Shouldn't it be `841.9542493` MHz instead of `8419.542493` MHz?\n\nLast, why must we re-position the satellite every five minutes? Can't we just keep the satellite focused on star A for 15 minutes and watch as the earth continues its orbit and the needle signals change frequency (via Doppler Effect)?"
    }
  ],
  "comments": [
    {
      "id": 1359341,
      "author_name": "CPMP",
      "author_url": "",
      "post_date": "2021-06-21T08:07:40.180000",
      "content": "<p>You need to be careful about unit conversions.  88.5 MHz = 8,000,000 Hz  is wrong.  Truth is:</p>\n<p>88.5 MHz = 88,500,000 Hz</p>\n<p>I cannot answer all your questions as I am not an astronomer, but here is one I can answer.</p>\n<blockquote>\n  <p>Within the Data Information section, at the bottom of the picture of the Voyager 1 snippet, I'm having trouble making sense of the horizontal scale.</p>\n</blockquote>\n<p>The scale ranges from 8,419,542,493 + 857 Hz (left) to 8,419,542,493 - 857 Hz (right).  What is counter intuitive is that values decrease from left to right.</p>",
      "votes": 2,
      "replies": [
        {
          "id": 1359345,
          "author_name": "Erik Kaufman",
          "author_url": "",
          "post_date": "2021-06-21T08:10:54.747000",
          "content": "<p>Thanks for the insight! Will fix the typo</p>",
          "votes": 0,
          "replies": []
        }
      ]
    },
    {
      "id": 1360051,
      "author_name": "glazed",
      "author_url": "",
      "post_date": "2021-06-21T18:53:15.980000",
      "content": "<blockquote>\n  <p>Last, why must we re-position the satellite every five minutes? Can't we just keep the satellite focused on star A for 15 minutes and watch as the earth continues its orbit and the needle signals change frequency (via Doppler Effect)?</p>\n</blockquote>\n<p>If a signal is coming from another star system, we can safely assume that the frequency will change significantly over time, but the converse doesn't necessarily hold. (Although the converse might not be such a bad bet with this particular data set.)</p>\n<p>A radio telescope is designed to measure the RF energy coming from a very narrow cone while canceling out any energy coming from different angles. This cancelation isn't perfect. Signals of interest are faint (because of distance) while many RF sources on Earth are strong (because of proximity). Inevitably, some signals from sources on earth leak into the measurements. If an interesting signal from a star doesn't vanish when the telescope points away, it wasn't really coming from that star.</p>",
      "votes": 0,
      "replies": [
        {
          "id": 1360474,
          "author_name": "Erik Kaufman",
          "author_url": "",
          "post_date": "2021-06-22T05:51:05.920000",
          "content": "<p>Thank you! I appreciate your help!</p>\n<blockquote>\n  <p>If an interesting signal from a star doesn't vanish when the telescope points away, it wasn't really coming from that star.</p>\n</blockquote>\n<p>Cool! So the odd-indexed recordings (where the telescope points away) are actually very helpful in determining if an interesting signal is interference or not. The signal is <em>not</em> interesting if the signal is still there in the next off-target recording.</p>",
          "votes": 0,
          "replies": []
        }
      ]
    },
    {
      "id": 1359879,
      "author_name": "yukiya",
      "author_url": "",
      "post_date": "2021-06-21T15:55:58.723000",
      "content": "<blockquote>\n  <p>how does a radio convert that FM signal to something listenable to the human ear? Is there some decoding going on?</p>\n</blockquote>\n<p>FM stands for Frequency Modulation. Yes, you need to decode it back from its carrier frequency (the 88Mhz)</p>",
      "votes": 0,
      "replies": [
        {
          "id": 1360475,
          "author_name": "Erik Kaufman",
          "author_url": "",
          "post_date": "2021-06-22T05:51:30.570000",
          "content": "<p>Sweet! Thanks for the tip :)</p>",
          "votes": 0,
          "replies": []
        }
      ]
    }
  ],
  "raw_markdown_by_id": {
    "1359341": "You need to be careful about unit conversions.  88.5 MHz = 8,000,000 Hz  is wrong.  Truth is:\n\n88.5 MHz = 88,500,000 Hz\n\nI cannot answer all your questions as I am not an astronomer, but here is one I can answer.\n\n> Within the Data Information section, at the bottom of the picture of the Voyager 1 snippet, I'm having trouble making sense of the horizontal scale.\n\nThe scale ranges from 8,419,542,493 + 857 Hz (left) to 8,419,542,493 - 857 Hz (right).  What is counter intuitive is that values decrease from left to right.\n\n",
    "1360051": "> \n> Last, why must we re-position the satellite every five minutes? Can't we just keep the satellite focused on star A for 15 minutes and watch as the earth continues its orbit and the needle signals change frequency (via Doppler Effect)?\n\n\nIf a signal is coming from another star system, we can safely assume that the frequency will change significantly over time, but the converse doesn't necessarily hold. (Although the converse might not be such a bad bet with this particular data set.)\n\nA radio telescope is designed to measure the RF energy coming from a very narrow cone while canceling out any energy coming from different angles. This cancelation isn't perfect. Signals of interest are faint (because of distance) while many RF sources on Earth are strong (because of proximity). Inevitably, some signals from sources on earth leak into the measurements. If an interesting signal from a star doesn't vanish when the telescope points away, it wasn't really coming from that star.",
    "1359879": ">  how does a radio convert that FM signal to something listenable to the human ear? Is there some decoding going on?\n\nFM stands for Frequency Modulation. Yes, you need to decode it back from its carrier frequency (the 88Mhz)",
    "1359180": "if an FM radio signal is running somewhere in the range containing 88.5 MHz = 88,500,000 Hz and the human hearing range is 20 Hz - 20,000 Hz, how does a radio convert that FM signal to something listenable to the human ear? Is there some decoding going on?\n\nWithin the [Data Information section](https://www.kaggle.com/c/seti-breakthrough-listen/overview/data-information), at the bottom of the picture of the Voyager 1 snippet, I'm having trouble making sense of the horizontal scale.\n- How can you calculate relative frequency in Hz from MHz? How can you have a negative frequency value of say -857 Hz? Is this just a standardized scale where we took the range from some amount `A` in MHz to some amount `B` in MHz, divided everything in that range by `1,000,000`, and then finally set `0` to be the average of `A` and `B` and normalized all other values appropriately?\n- Shouldn't it be `841.9542493` MHz instead of `8419.542493` MHz?\n\nLast, why must we re-position the satellite every five minutes? Can't we just keep the satellite focused on star A for 15 minutes and watch as the earth continues its orbit and the needle signals change frequency (via Doppler Effect)?"
  }
}