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RF transceiver with RSSI feature help

Discussion in 'Radio and Communications' started by ronnelabing, Jun 16, 2016.

  1. ronnelabing

    ronnelabing New Member

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    Hi! I want to use RF signal for my thesis project. I want the receiver to detect rf signal and set a signal strength threshold, if the threshold is reached the output on the receiver will be logic 1.. Can a cheap RF transceiver can be programmed to set signal threshold? And if can.. i want to know how to do the code.. I just need an rf with a range of at least 50 meters.. Can i get your opinion on this guys? please help
     
  2. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    The inexpensive super-regenerative 315 or 433MHz modules require sophisticated modulation schemes (timed On-Off-Keying) to provide a secure data link. Good online read about them. For reliable operation at 50m you will need at least a 1/2 lambda dipole antenna at either the receiver or the transmitter...

    It is not legal to leave these keyed for long periods. The rules for using these "license-free" frequencies state that the transmissions must be short and intermittent.

    What country are you in?
     
  3. ronnelabing

    ronnelabing New Member

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    Hi! thank you for the reply. The RF 433Mhz will do and i just need a shorter range i guess.. about 5-10 meters will do, my problem is can i program the RF module to set a signal threshold at the receiver side? Im new on this thing and i almost have zero knowledge on this.. Hoping to get some help from you guys to comply my thesis project.. Thank you in advance ! im from philippines bdw..
     
  4. dave

    Dave New Member

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  5. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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    Read the stuff on Roman's web site I linked to. There is no "threshold" on a super-regen receiver; only random pulsing if no signal is being detected, or the on-off detected keying envelope if receiving an on-off keyed carrier. The only way to tell if the receiver is detecting signal vs random noise is to look at the temporal information in the detected output signal using timing or possible tone detection. Read Roman's article very carefully. It explains this very well.

    The output from the receiver effectively differentiates the RF envelope from the transmitter. There is no output that is proportional to the "strength" of the received signal. If you are trying to "measure" distance between the transmitter and receiver, you will need a different kind of receiver (superheterodyne, or Tuned-Radio-Frequency).
     
    Last edited: Jun 17, 2016
  6. Mikebits

    Mikebits Well-Known Member

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    As I recall, the purpose of a thesis project is to demonstrate ones proficiency in a given area. A thesis project often includes a detailed write-up along with an analysis, and sometimes an oral exam. I would think you should be fairly far along in your studies, so for you to be asking for someone to provide you with code just amazes me. Anyways, Hope RF makes a module (RF12B) that provides a received signal strength indicator pin. You can get these modules from Sparkfun. The datasheet can be download from this link.
    http://www.hoperf.com/rf_transceiver/modules/RFM12B.html
    I'm sure you can find example code somewhere.

    RF12Brssi.PNG
     

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