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{
    "url": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/DDSWKXXS2AJCJPY34TVGIPIZUR4CUD6S/",
    "mailinglist": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/",
    "message_id": "[email protected]",
    "message_id_hash": "DDSWKXXS2AJCJPY34TVGIPIZUR4CUD6S",
    "thread": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/thread/DDSWKXXS2AJCJPY34TVGIPIZUR4CUD6S/",
    "sender": {
        "address": "grant (a) ghengineering.co.uk",
        "mailman_id": "74a4d29508634e669020884f51007f55",
        "emails": "https://mailman.amsat.org/hyperkitty/api/sender/74a4d29508634e669020884f51007f55/emails/"
    },
    "sender_name": "Grant Hodgson",
    "subject": "[amsat-bb]  Phase shift keying question",
    "date": "2009-06-22T13:05:43Z",
    "parent": null,
    "children": [],
    "votes": {
        "likes": 0,
        "dislikes": 0,
        "status": "neutral"
    },
    "content": "Andy\n\nI/Q modulators don't work that way, no free lunch and all that.  In newbie \nterms, an I/Q modulator can be thought of as a special mixer that can \nmodulate a carrier signal with an arbitrary modulation format - i.e. any type \nof modulation you want - literally.  \n\nAn I/Q modulator has a Local Oscillator input (carrier), an I input and a Q \ninput, and an RF output.  The modulation signal (FM, CW, AM, SSB, FSK, PSK or \nwhatever) is applied to both the I and Q inputs, which in turn modulate the \nLO signal to produce the output signal.\n\nThe type of modulation is determined by the phase relationship between the I \nand Q inputs.  Couple of simple examples - lets say the modulation signal is \na 1kHz sine wave, and we have an LO signal of 144.100MHz.  If both I and Q \ninputs are fed with this signal - in phase - then the output of the I/Q \nmodulator will be AM, at 144.100MHz, modulated at 1kHz - you will hear a 1kHz \ntone on an AM receiver.\n\nIf the I and Q inputs are fed 90 degrees out of phase with the same 1kHz \ntone, then the output of the modulator will be either LSB or USB depending on \nwhether the I signal leads or lags the Q signal.  If the receiver is set to \n144.100 kHz you will hear a 1kHz tone when set to the appropriate sideband.\n\nWith slightly more complex phase relationships between the I and Q signals it \nis possible to generate any type of modulation you want, and from a \nreceiver's point of view you will not know how the modulation was generated.\n\nBut you can't feed different modulation channels into the I and Q inputs - \nthe output would be a complex mixture of the two which would be un-\ndecipharable.\n\nYou could try Googling 'IQ modulation' for more information, although some of \nthe explanations are aimed at professional engineers with good maths skills.\n\nHTH\n\nGrant  G8UBN\n\n\nCould anyone please explain, in newbie terms, if it is possible to split a \ntelemetry data stream from a satellite OBC into two data streams, sent \nsimultaneously on two nbfm channels, each PSK with the phase difference \nbetween \nthem? \n\nI have in mind a conversation which I don't fully understand, about these \nbeing \nthe I and Q components, and this offering a doubling of the data rate \ncompared \nwith using one nbfm channel.\n\nGrateful for any pointers on or off the -bb\n\nmany thanks\n\nandy G0SFJ\n\n\n\n",
    "attachments": []
}