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µwave Comm.

Discussion in 'Radio and Communications' started by Electroenthusiast, Dec 25, 2011.

  1. Electroenthusiast

    Electroenthusiast Member

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    As we know, Microwaves are now used in almost all domestic communication. They are used in Mobile comm, Wif-fi, bluetooth, Microwave Ovens, Wireless & automation, etc.,
    How do they vary among eachother? As i've seen their frequency of operation remains same for all of the above.

    I've heard that Wi-fi uses a higher amplitude(voltage) wave, whereas bluetooth uses lower amplitude. Well, that's Okay, but how does a Wifi docket only pick up wifi signal, and bluetooth docket pick up only bluetooth signal.

    Again, there are three diff standards in wifi: 802.11b(B), 802.11g(G) and 802.11n(N). My modem works with all these standards, but how does the modem understand which standard is the wave received?

    This link gives a good information abt the interference b/w 2.4Ghz waves.
    Any links?
     
  2. 4pyros

    4pyros Well-Known Member Most Helpful Member

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    No thay are not all using "Microwaves" , only the oven. The rest use Radio frequency.
    http://en.wikipedia.org/wiki/Radio_frequency
     
    Last edited: Dec 26, 2011
  3. Electroenthusiast

    Electroenthusiast Member

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  4. dave

    Dave New Member

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  5. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    You're basically just assuming what frequencies things use - wireless and automation are mostly just UHF, no where near what are normally regarded as microwave frequencies.

    The definition on Wikipedia seems pretty bizzarre:

    http://en.wikipedia.org/wiki/Microwave

    Although is does mention that above 1GHz is generally considered microwave by RF Engineers - which is what I would generally agree with.
     
  6. nsaspook

    nsaspook Well-Known Member

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    Last edited: Dec 27, 2011
  7. 4pyros

    4pyros Well-Known Member Most Helpful Member

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    There is an over lap between Microwave and RF frequencies. The overlap is from 300MHz to 3GHz rang. I come from a back ground in two way radio communicatoins and would never consider WiFi and Bluetooth Microwave. The micro wave stuff I have worked on is huge. The radar on a the big ships will kill every sea gull around it for 50 feet when it is turned on, now thats Micro Wave not the thing you stik in your ear. Micro Waves can hurt and kill you, RF will not as easy.
     
    Last edited: Dec 27, 2011
  8. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    Bit of a limited definition :D

    Microwaves ARE RF frequencies, just a bit higher frequency than lower ones - the degree of power has no bearing on it.
     
  9. 4pyros

    4pyros Well-Known Member Most Helpful Member

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    Only that it can kill you!
    I dont know a better way to discribe the differance between RF and Microwaves that share the same band. Do you?
     
  10. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    There is no difference - Microwaves are simply one band of RF frequencies - the power has no bearing on it.

    Plenty of low frequency (even longwave) transmitters have used similar (and greater) powers, it doesn't make then Microwaves.
     
  11. trash

    trash Member

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    This statement is wrong, or it just doesn't make sense. Amplitude is usually with reference to power, not voltage. Though it can be expressed that way when referenced to a specific impedance.
    So what your trying to say is they use different power levels, but this really has nothing to do with the following question.

    They use different frequencies, even though they are in the same band.
    When there is an overlap they use different modulation and coding schemes.

    This is like saying you are locked in a room with several other people.
    half of you speak English, the other half speak French. There are of course some Americans in the room who also speak English, but they speak much louder than the other English speakers. :)

    Now Americans might not understand the other dialects of English, so other people may change the way they speak. Much slower and clearer for their American friends.
    This is basically how wifi works. Older equipment is recognised by newer versions and the most effective modulation scheme and data rate selected for each device.

    This quote is inaccurate and not correct anyway.

    If the power is the same then this statement is not true.
    VHF is more hazardous given the same EIRP.
    At higher frequencies submillimeter frequencies more power is reflected from surfaces.
    [​IMG]

    But as mentioned, microwaves are RF. There is no magic line where RF stops and microwaves begin. The properties from 300 MHz through to 30GHz change gradually.
    While a lot of us tend to say that everything above 1GHz is microwaves, and everything below is RF, 999MHz does not behave any differently to 1001MHz.
    And then of course we all officially recognise that "UHF < 3GHz < SHF" and then 2.99GHz isn't any different from 3.01GHz.

    The there is the point about splitting hairs. I'm not going to stick my head in front of 1kW of RF if it is 200MHz or 2GHz or 20GHz. Nor am I concerned if I am exposed to 1mW at the same frequencies.
     
  12. Electroenthusiast

    Electroenthusiast Member

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    Yes Nigel, it's bit Confusing. But, freq range says that they are Microwaves. I guess some ppl use the UHF,VHF...etc for naming them (instead of well accepted way like microwaves, x rays etc.,).

    hi Pyros, i guess there some confusion in the diff. b/w radio waves and radio frequencies.
    radio frequencies = all em wave freq = radio (waves), micro, infrared, visible, ultraviolet, xrays, gama, cosmic.
    radio waves = radio waves (portion) of em waves.
     
    Last edited: Dec 28, 2011
  13. Electroenthusiast

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    @TRASH

    Hi trash, any ref please... Because in schools we have been learning by expressing in terms of voltage. But any links that which can sprinkle something abt this will help me regarding this.

    Wi-Fi uses the same radio frequencies as Bluetooth, but with higher power, resulting in higher bit rates and better range from the base station. The nearest equivalents in Bluetooth are the DUN profile, which allows devices to act as modem interfaces, and the PAN profile, which allows for ad-hoc networking. Source: wiki/Bluetooth
     
  14. trash

    trash Member

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    I'm not sure which schools would be teaching RF in terms of voltage instead of power.
    There's a simple formula for converting dBuV into dBm. 0dBm = 107dBuV @ 50 ohms or 108.8dBuV @ 75 ohms RF power is almost always expressed in Watts or dBm (milliwatts). Occasionally the receive voltage is expressed in dBuV.

    The graph I posted above is the exposure levels from ARPANSA. Exposures are in watts per square metre.

    Sorry, I should be a little more clear about it. While some of the channels of bluetooth overlap with wifi, and they share the same spectrum and even their sidebands, they do not equally share frequencies. I'm trying to think of an example which is easier to visualise, but I'm finding it more difficult to describe this behaviour than I thought.
    Bluetooth has it's data smeared across the entire ISM band. Across 80 x 1MHz channels from memory.
    Wifi 802.11x has all of it's data in a single allocated (22MHz) channel. (I had to look that up). The wifi used bandwidth is only 1/4 of the bluetooth used bandwidth.
    They don't use the same modulation, or coding. Like the people in a room, they don't speak the same language. Even wifi channels overlap with other wifi channels.
    While there are collisions with data between any services using the bandwidth, each protocol uses error detection and correction techniques.

    So while there are data collisions, each user, protocol, service does not exclude the use of the others by their presence. Just because I share a room with you, and proximity with you, and I speak louder than you. This does not prevent you from holding an error free conversation with another person either in English or any other language. If for example I coughed and you missed what a person said, you might infer from the conversation what the missing word was. (forward error correction) Or, you could not ensure an accurate guess what word you missed. You might ask the person to repeat what they said. (backward error correction).


    Higher power does not in itself assure higher bit rates.
    Yes, higher power generally can be expected to produce better range.
     
    Last edited: Dec 29, 2011
  15. Electroenthusiast

    Electroenthusiast Member

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    Hi again Trash,
    We use Haykins Books for reference, and it's so there. I request any link/book for what you've said above. I would like to know more abt this.

    How do radiations from Microwave Oven differ with those used for communication purposes?

    Edit: Also, i found that 2.4Ghz/5Ghz reduces the costs. But How?
    Also is there anyway i know where i can get free SSIDs/Wifi(unpassword prot) access points in certain area? (Usually when travelling)
     
    Last edited: Dec 29, 2011
  16. Electroenthusiast

    Electroenthusiast Member

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  17. Electroenthusiast

    Electroenthusiast Member

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    How do radiations from Microwave Oven differ with those used for communication purposes?

    Also, i found that 2.4Ghz/5Ghz reduces the costs. But How?

    Also is there anyway i know where i can get free SSIDs/Wifi(unpassword prot) access points in certain area? (Usually when travelling)

    Also, i found that there are special plastic containers for Oven, dont you think that all plastic containers can be used???

    ?
     
  18. JimB

    JimB Super Moderator Most Helpful Member

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    Basically there is no difference, an electromagnetic wave is an electromagnetic wave.

    Having said that, the RF from a microwave oven is not very stable in terms of frequency and will drift around quite a bit, also there will probably be a lot of mains frequency hum (amplitude modulation).
    The RF is generated by a cavity magnetron with an unstabilised supply.

    The RF signal used for communications will be stable and on a well defined frequency. The frequency will probably be derived from a quartz crystal, assuring stability.

    No idea! Reduces cost compared with what?

    Switch on the laptop wireless card and let it search for nodes etc and try them.

    Some insulating materials exhibit high losses at high frequencies, and so they dont make for good capacitors in RF circuits.
    And they make really bad food containers for use in an microwave oven. The container dissipates the energy and gets hot rather than the food.

    JimB
     
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  19. Electroenthusiast

    Electroenthusiast Member

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    I learnt that it reduces cost when compared to other freq.
    Like using a 2.4GHz/5GHz waves will decrease the cost. SOURCE:Wiki

    Hey, i understood... but i need to stop each and every place in that case. I was asking like, if there a way in which the comp(/tablets) gives an alarm or shows in the display when a free access point is located(usually when traveling).

    Oh ok... anywhere i can research what kind of materials can be used?
     
  20. 4pyros

    4pyros Well-Known Member Most Helpful Member

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  21. Electroenthusiast

    Electroenthusiast Member

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    Last edited: Jan 7, 2012

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