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Modulations of signals . — Parallax Forums

Modulations of signals .

RITESH KAKKARRITESH KAKKAR Posts: 254
edited 2011-03-21 15:09 in General Discussion
Hi, i want to know exactly why we use cos wave for generating carrier signals??

Comments

  • Beau SchwabeBeau Schwabe Posts: 6,568
    edited 2011-03-14 22:04
    If your signal was DC then there would be no way to detect/distinguish it from the noise. By modulating your signal at a specific frequency, it's much easier to detect the presence of your signal because now you have a specific 'known' frequency to look for among the noise.

    The signal is sent using sine or cosine, but when receiving/detecting the signal the the I (In-phase) and Q (Out-Phase) are both looked at. The Q is always 90 Deg out of phase from I. The reason for this is so that you can still detect the presence of a signal by applying the Pythagorean theorem to I and Q. Doing so negates any Phase differences between the transmitter and receiver that there might be.
  • RITESH KAKKARRITESH KAKKAR Posts: 254
    edited 2011-03-14 22:12
    Hi, i want to know what will happen if we use Sin wave carriers signals??
  • Beau SchwabeBeau Schwabe Posts: 6,568
    edited 2011-03-14 22:16
    RITESH KAKKAR,

    You can use sine or cosine... the only difference between them is that one is 90 Deg out of phase with the other. On the receiver/detector end there would be no difference.

    Each point on the cosine wave occurs exactly 1/4 cycle earlier (90-Deg Phase difference) than the corresponding point on the sine wave, and it could be argued that therefore the propagation delay would be 1/4 cycle later if using Sine waves verses using Cosine wave when sending a signal, but in any case you need a complete period (usually several) of whatever frequency you are transmitting in order to get a valid detection on the receiver end.
  • RITESH KAKKARRITESH KAKKAR Posts: 254
    edited 2011-03-14 22:34
    OK, please what is the use of integrator as this i have readied in courses book, but i want know in practicals.
  • Beau SchwabeBeau Schwabe Posts: 6,568
    edited 2011-03-14 22:46
    RITESH KAKKAR,

    You need to provide more information about your reference. An integrator can be used to demodulate the received signal, but since there are several different transmission methods (i.e. AM,FM, etc) there are also several demodulation methods making it difficult to answer where and why an integrator might be necessary.
  • RITESH KAKKARRITESH KAKKAR Posts: 254
    edited 2011-03-14 22:49
    please, tell basic function of it as name applies it integrates.
  • RITESH KAKKARRITESH KAKKAR Posts: 254
    edited 2011-03-16 04:58
    reply.............
  • Mike GreenMike Green Posts: 23,101
    edited 2011-03-16 07:13
    Do not "bump" your thread to the top of the list by posting an "empty" message. It's impolite at best.

    The internet is full of sources of information including the Wikipedia. Perhaps you should start there since you're interested in relatively basic concepts. The Wikipedia has some excellent articles on a wide variety of basic electrical and electronics concepts. After carefully going through them and exploring the links provided, if you have specific questions, by all means ask here.
  • AleAle Posts: 2,363
    edited 2011-03-17 03:41
    Some loads of years ago there was a series of books called "Learn Rydio/TV/electronics/something-else in 15 days". I'm pretty sure similar books exist in libraries today and they provide a simple but driven curve to a topic as Radio. Specially if you do not know how to "dive" into the topic. Sometimes it happens to me that I read a word or some concept and I want to learn more... where do I start ? As Mike said Wikipedia is quite complete in many ways and today there are plenty of resource on-line to satisfy most curiosities. Universities for instance publish lectures on a variety of topics, also electronics. While many of them are just slide shows they provide some concepts that can help you start in a particular topic.
    In my case I learned a bit about modulation from a series of 6 books, translations from the english, about electronics with plenty of diagrams and explanations. They were from the 50s or 60s. Basic but full of useful info.
    Here is a link to one of these books, the English version... http://www.amazon.de/Basic-Electronics-3-Van-Valkenburgh/dp/B000UFRPXK/ref=sr_1_19?ie=UTF8&qid=1300358447&sr=8-19
  • RITESH KAKKARRITESH KAKKAR Posts: 254
    edited 2011-03-17 03:46
    Hi, the link you have how to download free book from it??
  • AleAle Posts: 2,363
    edited 2011-03-17 05:05
    The is no free download of that book, not even a digital copy, afaik. But you can get your free of digital interference copy in exchange for some money :), just send amazon the required amount and they will send you the book. You can read it then 24 hs a day every day of the week for as long as you want... day and night ! ;-).
  • Heater.Heater. Posts: 21,230
    edited 2011-03-17 05:22
    Just reminds me that I first learned anything about radio from the Teach Yourself series. Yes "Teach Yourself Radio" published in 1968 or so. With that book a young lad could build himself a crystal set up to a superhet. Sadly out of print now. Do youngsters have any such books available now a days?
  • RITESH KAKKARRITESH KAKKAR Posts: 254
    edited 2011-03-17 08:15
    Heater. wrote: »
    Just reminds me that I first learned anything about radio from the Teach Yourself series. Yes "Teach Yourself Radio" published in 1968 or so. With that book a young lad could build himself a crystal set up to a superhet. Sadly out of print now. Do youngsters have any such books available now a days?

    Hi, please tell free download books for me it will be great.

    thanks.
  • PublisonPublison Posts: 12,366
    edited 2011-03-20 16:26
    A polite question.

    Is Google blocked in the country of India?


    RITESH KAKKAR wrote: »
    Hi, please tell free download books for me it will be great.

    thanks.
  • RITESH KAKKARRITESH KAKKAR Posts: 254
    edited 2011-03-20 22:26
    What is this Infernal Machine??
  • FranklinFranklin Posts: 4,747
    edited 2011-03-21 15:09
    It's a "tag line" along with maybe http://en.wikipedia.org/wiki/Infernal_machine
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