Connect with us

Receiving a radio signal...

Discussion in 'Radio and Wireless' started by Externet, Feb 9, 2019.

  1. Externet

    Externet

    697
    142
    Aug 24, 2009
    Hi.
    When a radio receiver is tuned to say, 100 MHz; its local oscillator is at say 110.7MHz, the mixer stage produces a 10.7MHz intermediate frequency for later demodulation.

    If the broadcast ceases to emit, goes off the air;
    Or, shifting tuning to a blank unoccupied frequency;
    Or, shorting to ground the antenna input;
    is 10.7MHz still present at the mixer output ?

    And, do you know of an IC that can be used to detect the presence of 10.7 MHz ?
     
  2. davenn

    davenn Moderator

    13,164
    1,711
    Sep 5, 2009
    the 10.7 IF is only there when the RF and the LO are mixed
    if either is missing then there is no IF out

    And, do you know of an IC that can be used to detect the presence of 10.7 MHz ?

    a google search would have answered that for you.
    there are many IF IC's that have a 10.MHz input eg


    MC3357 --- NBFM dual conversion IF, 10.7MHz In, Audio out

    MC3359 --- NBFM dual conversion IF, 10.7MHz In, Audio out, less external components than 3357 and addition IF limiter stage

    MC3361 --- NBFM dual conversion IF, 2-8V supply, up to 60MHz I/P

    MC3362 --- NBFM dual conversion IF, 2-6V supply, usable with PLL, carrier detect indicator, up to 200 MHz I/P


    just some of the many in my own collection


    Dave
     
    Externet likes this.
  3. duke37

    duke37

    5,189
    704
    Jan 9, 2011
    Most FM radios have a muting control to turn off the sound if no signal is being received. The gain of FM recievers is very high and if there is no signal then detected noise produces a rushing noise.
     
  4. Externet

    Externet

    697
    142
    Aug 24, 2009
    Thanks, gentlemen.
    Dave : I meant knowing if 10.7MHz is present. No audio detection desired. To work on silent unmodulated signals. My searches found complete receivers as your suggested chips.
    Intention is to know if a carrier is present, on a receiver chip that does not have tuning indicator feature. Perhaps using a section of some other chip that could be added to an existing receiver.
    Will explore portions of the MC3362, for presence of 10.7MHz telling there is carrier.
     
  5. Ylli

    Ylli

    179
    30
    Jun 19, 2018
  6. Audioguru

    Audioguru

    2,480
    550
    Sep 24, 2016
    I agree that the 10.7MHz from the mixer will never be zero. It will have either signal or noise. Maybe its muting circuit detects the amplitude fluctuations of the noise?
     
  7. davenn

    davenn Moderator

    13,164
    1,711
    Sep 5, 2009

    As I stated before

    If either the LO signal or the RF signal is absent, there will be NO 10.7MHz IF signal generated (in the mixer) that then goes to the IF input pin of the IF IC
     
    Cannonball likes this.
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-