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receiving a carrier

Discussion in 'Electronic Design' started by jhon1, Dec 21, 2006.

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  1. jhon1

    jhon1 Guest

    Hello All.
    I am a beginner, all I need is to build a transmitter that only
    transmits a carrier without any modulation and be able to receive this
    carrier at the second location.
    unfortunaitly, most receiver circuits that are available over the
    internet use a different techniques such as superhet, which is not
    suitable for my application, I need to receive the carrier only with
    the same frquency as I sent it.
    please try to help me.
  2. If you do not want to mix down, then you will have to build a selective
    amplifier for the frequency you use.
    What frequency is that? Are you allowed to use it?
    Normally one would use LC tuned circuits, or perhaps xtals at the frequency
    you want, the issue is stability, if the input picks up any of the signal
    from the next stages, then you have a problem.
  3. jhon1

    jhon1 Guest

    thanks Jan
    do you have any simple circuit that can perform that.
    can I add selective amplifier for a definite frquency to any superhet.
    receiver (may be commercial radio), to isolate the desired high
    frequency carrier without mixing?!
  4. You need to undertsand what is going on a bit. On a normal radio, you are
    not interested at all in the 'carrier', except as a 'carrier', of the
    modulated data (hence the name). It is harder to amplify high frequency
    signals, than those at lower frequencies (limitations of the amplifiers
    themselves), and to really accurately tune them, so what was done, was to
    start by amplifying the signal a little, then immediately mix to produce a
    lower working frequency (the I.F. - intermediate frequency), and
    amplify/tune this. This is the 'superhet'. This also has the big advantage
    that for a 'tuneable' radio (that can be used to receive different
    adjacent bands), the RF tuning can be quite wide band, and by changing the
    mixing frequency, the _same_ IF can be produced for different incoming
    frequencies. The IF tuning can be accurately set, and quite narrow band.
    to give good selectivity.
    Now, if you want to look at the incoming carrier itself, there is
    absolutely no point at all, in getting involved in a superhet. After the
    first stage, the signal will already be at a lower frequency, and will not
    give you access to the 'carrier'. Instead do a search for 'T.R.F.' (tuned
    radio frequency). This is a much simpler radio design, which relies on
    just a tuned RF stage, and amplification at the RF frequency. Normally, a
    envelope detector is then used to get the amplitude modulation on the
    carrier, but without this, such a radio, will give direct access to the
    incoming 'carrier'. Historically, getting good gain/selectivity with such
    designs, was quite hard, but a number of basic IC's exist to do this. The
    ZN414, and it's latter descendants, was probably the most famous, and
    though this is no longer available, the MK484 is an almost direct

    Best Wishes
  5. A few important questions:

    What's the frequency?

    How far does it have to go?

    How clean does the received signal have to be?

    How much power is available at the transmitter and receiver?

    What country's radio laws apply?
  6. No way can I answer that as yo udo not give:
    1) frequency.
    2) required bandwidth.
    3) signal strength expected.
    It would perhaps be simpler to build a separate receiver.
    Please answer 1,2,3 questions above.
  7. maxfoo

    maxfoo Guest

    Forget designing your own rvcr/xmt unit. The way to go these days is to just add
    a module to your pcb. I like RF monolithics transceivers, they comes in
    different frequency flavors.
  8. Phil Allison

    Phil Allison Guest

    ** Desperate Groper Alert .

    ** Here's how you do it:

    1. Get yourself and old 27 MHz CB radio.

    2. Strap the mic button down, but don't say anything into it.

    3. Get a " Signal Strength Meter" - looks like a VU meter with an short
    antenna on top.

    4. The needle on the meter will show you if the carrier exists and indicate
    its relative strength at a distance.

    10- 4 li'll buddy..........

    ......... Phil
  9. kell

    kell Guest

    I wonder what for.
    You won't have anything to listen to at the receiver if you execute the
    scheme you describe.
    I'm no expert, but I think you may get a whistling sound during tuning
    or when the frequency drifts. Isn't that what happens when you're
    tuning around on sideband and you come across an AM carrier?
    Why don't you just get a shorwave receiver, build some kind of a simple
    tank circuit for your transmitter, and play around with them. You
    might learn something. From the vagueness of your first post nobody
    can really advise you anyway.
  10. Google "superregen" or "super regenerative receiver" and other
    variants.Super-regenerative receivers are popular in applications such
    as garage door remote, car alarm systems and wireless door chimes. They
    are ideal where information rate and cost are low.

    If you want to design your own, let me know; however, it may be
    challenging for a beginner. There are some examples on the web, as well
    as some commercially available units.

    Super-regenerative receivers are used often at 210, 280, 312, 315, 390,
    418, 434 MHz. I have also seen applications at 2441 and higher.

    This type of receiver works like this: An RF amplifier with positive
    feedback (at inteded receive frequency) is allowed to go in and out of
    oscillation at a rate called the quench frequency. Sometimes the quench
    is forced externally, and sometimes a single transistor is biased and
    configured such that the RF transistor serves also as the quench
    oscillator (self quenching).

    If you do it right, you can build a single-transistor receiver for a
    few pennies. Sensitivity is about 10uV with 75 ohm input. YMMV. In
    commercial applications, the challenging part of the design is meeting
    regulatory agency approvals, especially passing the "unintentional
    radiator" criteria.

    Frank Raffaeli
  11. Greg Neill

    Greg Neill Guest

    Maybe this will give you some ideas:
  12. Jon

    Jon Guest

    Any commercial receiver can do this. In the early days of Ham radio
    where Morse code was used, this is exactly what was done. The
    transmitter sent an "unmodulated" carrier that was interrupted to
    generate the code. At the receiver end, the carrier was mixed with the
    output of a local oscillator that was tuned slightly "off" from the
    received carrier frequency. The result was an audio signal equal in
    frequency to the difference between the carrier frequency and the local
    oscillator frequency. This gave an audible indication of the presence
    or absence of the carrier.
  13. And the problem with a phase lock loop is?

    Many thanks,

    Don Lancaster voice phone: (928)428-4073
    Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
    rss: email:

    Please visit my GURU's LAIR web site at
  14. jhon1

    jhon1 Guest

    Hello Ancient hacker
    the frequency may be any thing, this is not my question, ok say it is
    100 M, for 0.5 Km distance.
    My question is what is the way to receive a non modulated carrier, if I
    have an oscillator and antena, I can transmite high frequency carrier
    without any modulation, now I want to receive that carrier ( and when
    examine it, it must be the same frequency and shape of the same
    transmitted carrier), how I can perform that?
  15. jhon1

    jhon1 Guest

    hello Jan
    I am asking about the concept, but let us say 1) 100 M
    2)to be transmitted 0.5 km
  16. jhon1

    jhon1 Guest

    hello Phil
    you don't understand my question
  17. jhon1

    jhon1 Guest

    Hello Kell
    yes I don't want to listen to any thing, but I have another
    application I want to do
  18. Joel Kolstad

    Joel Kolstad Guest

    Umm... if you hook up an antenna that's resonant at more or less 100MHz, the
    signal out of the antenna will be the carrier you transmitted -- with lots of
    attenuation, of course.

    As a first order approximation, there's no difference between a tuned
    transmitting/receiving antenna system and a big attenuator. In other words,
    you can simulate your wireless system by just connecting up your transmitter &
    receiver with a cable and, say, a 60dB pad inbetween. (Throw in an extra
    arbitrary phase shift if you'd like -- use a random length of coax cable.)

    It sounds like you don't have much experience here... could you tell us what
    you're trying to accomplish? Why a superheterodyne architecture won't work?
    When you say "it must be the same frequency" does that include accounting for
    things like doppler shifts? What does "the same shape" mean if you aren't
    modulating the carrier?

  19. jhon1

    jhon1 Guest

    Thanks Joel
    I am working on a project to transmite a clock signal (just binary
    sequence or square wave), and one of the solutions is to send a sine
    wave ( high frequency carrier) and squarising it at the other side, so
    how I can achieve like this task?

  20. Have fun then. There are many, very valid reasons that you don't see
    receivers that are not superhetrodyne.

    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
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