Radio bands

Discussion in 'Wireless & RF Design' started by PRS, Dec 18, 2008.

  1. PRS

    Thread Starter Well-Known Member

    Aug 24, 2008
    989
    35
    I'm interested in RC. I want to use CW with my own 8-bit code. My question is whether or not I can use the 27 MHz RC band to do this -- given my unique code and the fact that I observe the standard channels. Also, I notice the 1.84 - 2 Megahertze is open to CW operators with licenses. My question here is whether or not it is legal to use this band for this project. When I say CW, I mean it to be switched at a rate of 50 kbits per second.
     
  2. leftyretro

    Active Member

    Nov 25, 2008
    394
    2
    Without knowing which country you would be operating (why do so many poster not set up their profiles?) in it's quite hard to answer your question as the answers have more to do about laws and regulations rather then technical possibilities.

    That aside, 1.84-2mhz is a licenced ham band in many countries and would require a licence, however from a technical point that band would be a poor choice because of antenna inefficiencies of any size that would fit on a R/C model.

    Also keep in mind that a 50kps signal would require a rather wide bandwidth and would be not be legal in most licenced bands in the HF spectrum, such as the 'CB' band in the 27mhz range, it would 'occupy' more then one channel.

    Lefty
     
  3. garry.owens

    Member

    Dec 17, 2008
    17
    0
    i do beleive that you do not acually mean the cb band but the radio control model band which in most countrys is100khz wide this i do believe would be possable but you may come across othere law proplems as this equpment has to be build to a licence but if you whish to experament then try it on verry low power i meen around 100 mw then you will not cause to much proplems other wise find a nice frendly local ham operator who will help you by alowing you to try it on his licence
     
  4. bertus

    Administrator

    Apr 5, 2008
    15,650
    2,348
    Hello,

    A licence is personal. It can not be used by another person.
    50 kb/ps will give a large spread spectrum, this will not be appreciated by other users in th CB band.

    Greetings,
    Bertus
     
  5. PRS

    Thread Starter Well-Known Member

    Aug 24, 2008
    989
    35
    Here are the specific channels assigned to the 27 MHz radio control band:

    1) 26.995
    2) 27.045
    3) 27.095
    4) 27.145
    5) 27.195
    6) 27.255

    Notice there is +/-50 kHz between each channel. This is why picked 50 kHz band width. But I certainly don't need that much. I can use whatever a crystal filter gives me. The receiver is just treating each pulse as a bit in an 8-bit data string.
     
  6. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    The bandwidth you will use relates to the data transmission frequency.
     
  7. leftyretro

    Active Member

    Nov 25, 2008
    394
    2
    While those channels are assigned for R/C use only, there are standard CB voice channels BETWEEN those assignments. So there is not +/- 50khz of free space between those assigned R/C channels. A signal that occupies more then the channel spacing (10khz) will cause adjacent channel interference and those channels will interfere with your R/C receiver if it's set up to handle that high data rate channel bandwidth. Modulation method and rate determines how much bandwidth a transmission occupies within the band. Here is a list of the CB channel frequencies.

    http://home.att.net/~wizardoz/cbmw/channels.html

    Lefty
     
  8. PRS

    Thread Starter Well-Known Member

    Aug 24, 2008
    989
    35
    Thank you, very much. This was exactly what I needed to know. Right now this transmitter/receiver combo is in embryo. Just a possible scheme to create rf control of a distant object. Note the method of sending data is simply CW fashion using my own 8-bit code, sort of like RTTY. This is all theoretical right now, but clocks will be used with both transmitter and receiver to count 8 "bits", the last one being used for a 'start'/reset marker. This gives me either 7 lines to switch motors and relays or 7 logic lines should I go that route. Does it sound feasible or am I missing something?
     
  9. PRS

    Thread Starter Well-Known Member

    Aug 24, 2008
    989
    35
    The 50 kb is not in a package, there is no modulation here, just on/off radio wave decoded at the receiver.
     
  10. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
    2,040
    287
    49 MHz is also allocated to radio control in the US.
     
  11. PRS

    Thread Starter Well-Known Member

    Aug 24, 2008
    989
    35
    But I'm not modulating the information in a package 50kz wide. I'm simply sending a switched on/off radio wave and interpreting a code (my own) at the receiver.
     
  12. PRS

    Thread Starter Well-Known Member

    Aug 24, 2008
    989
    35
    Thanks. I have a vague memory of that, and it's well-within the frequency range of my test equipment. Perhaps you can answer this: For a fixed amount of transmission power does a higher frequency propogate farther than a lower frequency? I'm speaking line of site remote control.
     
  13. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
    2,040
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    Might I suggest you read the attached article on the bandwidth of a CW signal. http://www.w8ji.com/cw bandwidth analysis.htm


    As an ABSOLUTE BARE MINIMUM, your bandwidth would be 100KHz with 50 khz data rate. If your signal is anything resembling a square wave, your bandwidth will be three to five times that amount.

    I wonder what possible RC application could need a 50kc data rate anyway?

    Eric
     
  14. beenthere

    Retired Moderator

    Apr 20, 2004
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    For line of sight, frequency isn't too important. A good receive antenna makes more difference.
     
  15. leftyretro

    Active Member

    Nov 25, 2008
    394
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    Very correct. For line of site use the higher the frequency the more efficient and smaller the receiver's antenna can be so VHF and UHF are the most popular choice these days.

    Lefty
     
  16. RAH1379

    Well-Known Member

    Dec 13, 2005
    69
    1
    get an amateur license and use the 6 meter band, there are allocations there for rc control and plenty of bandwidth.a technician class is all you need.
     
    Last edited: Apr 15, 2009
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