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  • This is a simple 27MHz FM-CB receiver circuit built with TCA440 for listening CB ( citizen’s band ) transmissions with FM (frequency modulation). The selection is made with ceramic filters. This 27 MHz receiver works with an intermediary frequency of 455 kHz. The input filter is 27 MF type, so we obtain an acceptable attenuation of the mirroring frequency.

    CB 27MHz Receiver Circuit Schematic

    cb fm 27mhz receiver circuit diagram

    Because the intermediary frequency filter is used without adapting transformer, the selection is at 40 dB. Because of the noise in the transmission pauses, the CB receiver circuit has a squelch circuit which reacts at 4.5 kHz domain noise.

    
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    12 Responses to "27MHz CB Receiver Circuit"

    1. Where is the coil winding details????????????

    2. There are no details, the coil has a serial number KXC/K3265

    3. i don’t understand the cct

    4. he he the most disgusting part of a transmitter the coil isnt explaned

    5. Just one more circuit copied from Elektor without giving credit to the magazine.

      • Ted, please send us more information about your comment because we are receiving emails with these circuits in pdf formats and then publish them. If it is from Elektor we will give them credit or remove the article if necessary. Use the Contact Us page.

      • You can recognize Elektor schematics from their appearance; this one is certainly coming from that magazine.
        Anyway, besides the hard to find coil, both ceramic filters tuned at 27 MHz (FI1 and FI2) will be nearly impossible and/or expensive to get.

    6. Never mind the magazine credit, WTF is this :|
      “…for listening CB ( citizen’s band ) transmissions with FM (frequency modulation…”
      FM ? On Citizen’s Band ?
      Dear friends, THERE IS NO FM on the 27Mhz Citizen’s Band!
      There may be SSB – Single Side Band, which was institued when they went from 23 to 40 channels, but the first 23 are Amplitude Modulated, not Frequency Modulated.
      IMHO, that is…

    7. hassan delghavi says: on March 26, 2014 at 4:52 pm

      hi to every one i am comment from Iran please help me about one simple 27mhz receiver map pll . schématic diagram
      thank you very much .

    8. Anil Akbulut says: on June 12, 2014 at 1:37 pm

      what are ic2 and ic3 on the right top of circuit. i did not understand

    9. PrashanthSuvarna says: on June 26, 2014 at 8:05 pm

      To follow & make some sense of the circuit, u have 2 put2gether whatever it is that the author has said about it. Then follow what some useful pints are put2gether by other observers, finally this my observations on the same. TCA440 is /was often used in the fm demod section on many Tv receivers. It is made(persuaded) to detect/demod 27Mhz signals. The circuit is fairly straight forward except perhaps4the hard2find parts like the cer filters&the associated rf transformer/coil as it is referred here.Now assuming u have Fm reception transmission in your area, The signals will get processed in the IC&the coil&proceed2the audio amplifier Lm386. The 741 here is cleverly used as a straight4ward Rf amplitude detector whose opt is further processed by the opt stage of this IC. This is used 2avoid the annoying Fm Noise put out by many such circuits of the day and nay be an imp addition2avoid the rather intrusive racket produced when u tune betwwen the stations/ whenever there is no transmission.Personally I think Its an imp addition. U may do awy with all the associated components without any drop in the primary performance of the circuit.Now finally….Fm is the “latest Kid on the block” where Cb@27Mhz is concerned in many countries.In fact it is even mandated by law in Great Britian/elsewhere. Am/Fm option is included in many 27Mhz Cb units sold@lots of places,& O Btw, & do 4give my Sms Eng.Have2use it2get as much info inorder2 “fill in the blanks”2overcome the small word space limitation,sorry folks.Bye(;-)

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